Proteins Genetic Code 4b'

Summary

This lecture delves into the translation process of the genetic code, detailing how scientists deciphered the genetic code table using various nucleotide combinations and the ribosome binding assay. It explains the universality and degeneracy of the genetic code, the role of start and stop codons, and the interaction between codons and anticodons on tRNAs. The lecture also covers the wobble hypothesis, isoaccepting tRNAs, and the process of amino acid activation and charging of tRNAs by aminoacyl-tRNA synthetases. Finally, it touches on the structure and function of ribosomes, setting the stage for a deeper exploration of translation's initiation, elongation, and termination stages in subsequent lectures.

Takeaways

• 🧬 The genetic code is deciphered through various experiments involving nucleotide combinations and ratios.
• 🔬 Scientists used different ratios of nucleotides like two U for every C to calculate the ratios and measure amino acid formation.
• 🧪 Ribosome binding assays developed by Nierenberg and Leder helped to definitively solve the genetic code for every single codon.
• 📚 The genetic code is a triplet code, with each codon made up of three nucleotides, and it is continuous and non-overlapping.
• 🌐 The genetic code is nearly universal across organisms, with a few exceptions in some organisms like mitochondria and certain protozoa.
• 🔄 The genetic code is degenerate, meaning multiple codons can code for the same amino acid, providing redundancy.
• ⏹ There are three stop codons that signal the end of protein translation and one start codon (AUG) that initiates translation.
• 🔀 The interaction between codons and anticodons on tRNAs is crucial for protein synthesis, with wobble allowing for flexibility in base pairing.
• 🔋 Amino acids are attached to their specific tRNAs through a two-step process involving aminoacyl-tRNA synthetases and ATP hydrolysis.
• 📉 Translation occurs in three stages: initiation, elongation, and termination, with ribosomes playing a central role in protein synthesis.

Q & A

What is the significance of dinucleotides, trinucleotides, and tetranucleotides in the genetic code?

Dinucleotides, trinucleotides, and tetranucleotides are significant in the genetic code because they were used in experiments to understand how different nucleotides could combine. By varying the ratios of these nucleotides, scientists could deduce the ratios of amino acids formed and thus determine which codons coded for which amino acids.

How did the ratio of U to C nucleotides affect the formation of nucleotide combinations?

By altering the ratio of U to C nucleotides, scientists could influence the likelihood of forming certain dinucleotides like UCU or CUU over others, such as all Cs. This manipulation helped them calculate the ratios and measure the amino acids that formed, aiding in decoding the genetic code.

What was the role of polynucleotides in decoding the genetic code?

Polynucleotides, such as polyU, polyG, polyC, and polyA, were used in assays to change the ratio of different nucleotides. This allowed scientists to experiment with different combinations and ratios, which was crucial in decoding the genetic code.

What technique helped scientists to definitively solve every codon in the genetic code?

The ribosome binding assay, developed by Nirenberg and Leder, was the technique that helped definitively solve every codon in the genetic code. This assay allowed for the binding of tRNA molecules to a ribosome mRNA complex in the absence of protein synthesis, enabling the synthesis of known three-nucleotide codons.

How did the ribosome binding assay work in the context of decoding the genetic code?

In the ribosome binding assay, tRNAs bound to different amino acids were introduced to a specific codon. The tRNA that matched the codon would bind to the ribosome. Unbound tRNAs would pass through a filter, while ribosomes with bound tRNAs would be caught. This allowed scientists to detect which amino acid was bound to the tRNA inside the ribosome.

What is the significance of the genetic code being nearly universal?

The near universality of the genetic code means that almost all organisms share the same code. This allows for the transfer of genes between different organisms in research and genetic engineering, as the genetic code functions similarly across species.

What does it mean for the genetic code to be degenerate?

The genetic code is degenerate because multiple codons can code for the same amino acid. This means that there is more than one way to code for each amino acid, providing redundancy in the genetic code.

What are start and stop codons, and how do they function in protein synthesis?

Start codons, such as AUG, signal the beginning of protein synthesis. Stop codons, on the other hand, signal the cell to stop translating. There are three specific codons for stop and one for start, which are crucial for controlling the process of translation.

How do codons interact with anti-codons during protein synthesis?

Codons on mRNA interact with anti-codons on tRNA through complementary base pairing. The anti-codon of the tRNA is in a three-to-five prime order and matches the five-to-three prime oriented codon on mRNA. This interaction is essential for the correct amino acid to be added to the growing polypeptide chain.

What is the role of aminoacyl-tRNA synthetases in protein synthesis?

Aminoacyl-tRNA synthetases are enzymes that attach the correct amino acid to its corresponding tRNA, ensuring that the tRNA is 'charged' with the appropriate amino acid. They recognize the tRNA's anticodon and sometimes other regions of the tRNA to perform this task accurately.

How does the process of translation occur in three stages?

Translation occurs in three stages: initiation, elongation, and termination. Initiation involves the binding of mRNA to the small ribosomal subunit, the initiation tRNA, and the large ribosomal subunit. Elongation is the process of adding amino acids to the growing polypeptide chain. Termination occurs when a stop codon is reached, signaling the end of translation.

Outlines

00:00

🧬 Lecture on Translation and the Genetic Code

The lecture delves into the exploration of the genetic code through various experiments involving nucleotides. The speaker discusses how different nucleotides were combined in various ways to form dinucleotides, trinucleotides, and tetranucleotides. They explain how altering the ratio of U and C nucleotides could impact the formation of amino acids and how these ratios were used to decipher the genetic code. The lecture also touches on the use of polynucleotides and random copolymers to further understand the genetic code. A significant breakthrough came with the development of a ribosome binding assay by Nirenberg and Leder, which allowed for the definitive mapping of codons to amino acids by synthesizing known three-nucleotide codons and observing which amino acids would bind. This method revolutionized the understanding of the genetic code.

05:00

🌐 Characteristics of the Genetic Code

This section highlights the universality and degeneracy of the genetic code. The genetic code is nearly universal across organisms, with few exceptions like mitochondria and some protozoa. The code is degenerate, meaning multiple codons can code for the same amino acid, providing redundancy. The lecture also discusses the concept of start and stop codons, which are crucial for initiating and terminating protein synthesis. The interaction between codons and anticodons on tRNAs is explained, emphasizing the importance of base pairing and the role of 'wobble' at the third position of the anticodon, which allows for flexibility in codon recognition. The existence of isoaccepting tRNAs, which can carry the same amino acid but have different anticodons, is also mentioned.

10:02

🔬 Details of Translation and the Role of tRNAs

The paragraph focuses on the process of translation, where the genetic message in mRNA is translated into a polypeptide chain. It describes the directionality of translation, with the mRNA being read from the 5' to 3' end, and the polypeptide being synthesized from the N-terminus to the C-terminus. The role of tRNAs in translation is emphasized, with each tRNA carrying a specific amino acid and having an anticodon that matches the mRNA codon. The concept of 'charging' tRNAs, where amino acids are attached to their corresponding tRNAs, is introduced. The process involves two steps: activation of the amino acid by ATP and transfer to the tRNA. The lecture also mentions the role of aminoacyl-tRNA synthetases, enzymes that ensure the correct amino acid is attached to the correct tRNA.

15:06

🧪 Experiments on tRNA and mRNA Recognition

This part of the lecture discusses experiments that were conducted to understand how mRNA recognizes tRNAs. The speaker describes an experiment where the amino acid carried by a tRNA was chemically altered to determine whether the mRNA recognizes the anticodon or the amino acid itself. The results showed that the mRNA only recognizes the anticodon, not the amino acid, as a tRNA with an altered amino acid was still recognized and incorporated into the growing polypeptide chain. This finding underscores the specificity of the genetic code and the importance of the anticodon in translation.

20:06

📚 Overview of the Translation Process

The final paragraph provides an overview of the translation process, which involves three main stages: initiation, elongation, and termination. The paragraph describes the initiation phase, where the mRNA binds to the small ribosomal subunit, the initiation tRNA binds to the small subunit, and the large ribosomal subunit joins the complex. The lecture concludes with a mention of the upcoming discussion on the elongation and termination steps in the next lecture. The paragraph also touches on the structure of ribosomes and their role in facilitating translation, with mRNA and tRNAs fitting into specific sites within the ribosome to carry out protein synthesis.

Keywords

💡Dinucleotides

Dinucleotides are molecules consisting of two nucleotides linked together by a phosphodiester bond. In the context of the video, dinucleotides are part of the early experiments to understand the genetic code, where different combinations of nucleotides were used to predict how they would assemble into larger units and influence the formation of amino acids.

💡Trinucleotides

Trinucleotides, also known as codons, are sequences of three nucleotides that are the basic units of the genetic code. The video discusses how trinucleotides were used in experiments to decipher the genetic code, showing that specific codons correspond to specific amino acids, which are the building blocks of proteins.

💡Ribosome Binding Assay

The ribosome binding assay is a technique mentioned in the video that was pivotal in solving the genetic code. It involves tRNA molecules binding to a ribosome mRNA complex in the absence of protein synthesis. This method allowed scientists to synthesize known three-nucleotide codons and determine which amino acid would bind to them, thus helping to definitively solve the genetic code.

💡Codon

A codon is a sequence of three nucleotides on mRNA that specifies a particular amino acid. The video explains how the ratio of different nucleotides and the formation of codons were crucial in understanding the genetic code. The term is central to the video's theme as it directly relates to the mechanism of protein synthesis.

💡Amino Acids

Amino acids are the building blocks of proteins, and the video discusses how the ratios of amino acids formed were measured to help decode the genetic code. Each amino acid is coded for by at least one codon, and the video highlights the importance of understanding which codons correspond to which amino acids.

💡tRNA

Transfer RNA (tRNA) is a type of RNA that translates the genetic code from mRNA into proteins by bringing the correct amino acid to the ribosome for protein synthesis. The video describes how tRNA molecules with specific anticodons bind to the codons on the mRNA, facilitating the process of translation.

💡Anticodon

An anticodon is a sequence of three nucleotides on a tRNA molecule that is complementary to the codon on mRNA. The video explains the importance of the anticodon-codon interaction in ensuring that the correct amino acid is added to the growing polypeptide chain during protein synthesis.

💡Wobble Hypothesis

The wobble hypothesis, discussed in the video, refers to the flexibility in the base pairing between the third base of the codon and the first base of the anticodon. This flexibility allows a single tRNA to recognize more than one codon, which is essential given the redundancy of the genetic code.

💡Isoaccepting tRNAs

Isoaccepting tRNAs are different tRNA molecules that can carry the same amino acid but have different anticodons. The video mentions these as an example of how multiple tRNAs can correspond to a single amino acid, highlighting the complexity and efficiency of the genetic code.

💡Start and Stop Codons

Start codons, such as AUG, signal the beginning of protein synthesis, while stop codons signal the end. The video explains that while most codons code for amino acids, these special codons have different functions: initiating and terminating the translation process.

💡Aminoacyl-tRNA Synthetase

Aminoacyl-tRNA synthetases are enzymes that attach the correct amino acid to its corresponding tRNA during protein synthesis. The video describes this process as a two-step reaction that requires ATP and ensures that the correct amino acid is placed on the correct tRNA, which is essential for accurate protein synthesis.

Highlights

Lecture discusses the process of deciphering the genetic code and the methods used.

Different nucleotides were combined in various ways to understand their roles in the genetic code.

The ratio of nucleotides was altered to form different nucleotide combinations, influencing the amino acid formation ratios.

By measuring amino acid ratios, scientists could deduce the codon coding for specific amino acids.

Polynucleotides like polyU, polyG, polyC, and polyA were used to change the nucleotide ratios.

Ribosome binding assay developed by Nierenberg and Leder helped to definitively solve the genetic code.

The assay allowed for the synthesis of known three-nucleotide codons to match specific amino acids.

The genetic code is a triplet code, with each codon consisting of three nucleotides.

The genetic code is continuous and non-overlapping, reading every three nucleotides without skipping.

The genetic code is nearly universal, with minor exceptions in some organisms like mitochondria.

The code is degenerate, with multiple codons coding for the same amino acid.

Methionine has a special start codon, AUG, which initiates protein synthesis.

There are three stop codons that signal the end of translation.

Anticodons on tRNAs interact with mRNA codons through complementary base pairing.

Wobble base pairing allows for some flexibility in the third nucleotide of the codon.

Isoaccepting tRNAs can have different anticodons but carry the same amino acid.

Translation is the process of converting the genetic message from mRNA into a polypeptide chain.

The ribosome is the site of protein synthesis, where mRNA and tRNAs interact.

Translation is divided into three stages: initiation, elongation, and termination.

Transcripts

okay so this is the second lecture in

the lecture set on translation and the

genetic code all right so I apologize

bit of a rough stop at the end of that

first lecture in this set um so I was

talking about they would have these

different dinucleotides trinucleotides

tetranucleotides and they would randomly

go together um and the other thing they

could do is so they could put together U

and C but not as a d nucleotide but they

put U and C together and they'd alter

the ratio so they'd put two U for every

C so you'd more likely get a U or a ucu

or a cuu um than you were to get all C's

or a couple of C so they could calculate

the ratios and then they could then

measure the ratio of the amino acids

that formed and they could go back and

sort out um what codon coded for what

amino acids so by doing all these

different combinations of ratios of

different nucleotides making D TR

nucleotides all those different things

they able to solve actually most of the

genetic code table but do weren't quite

able um to get it all doing it that way

until they um worked on another

technique which we talk about in a

minute so as I mentioning there they

could use all of one polyu polyg polyc

polya random copolymers and there they

could again change the ratio of the

different nucleotides together known

copolymers these are the known

dinucleotides tri-nucleotides that we

just saw on um this slide here and the

final uh type of assay that was

developed really helped them to

definitively solve for every single

codon and this was a ribosome binding

assay so uh nerber and leader developed

a ribosome binding assay where the tRNA

molecules would bind to a ribosome mRNA

complex in the absence of protein

synthesis so they're able to come up

with a technique where they actually

didn't have to

translate all they needed was the TRNA

that was bound to an amino acid to bind

to a ribosome and mRNA and important for

this is they could then synthesize known

three nucleotide codons so they could

put together exactly in in the order in

which they wanted three nucleotides so

they knew exactly what the codon was and

that worked in this system so they

didn't have to do all this random type

of thing they could put together the

three nucleotides they wanted and then

they knew exactly which amino acid would

bind that so um what does that look like

so again a still cell free or sorry this

is the um first methodology I forgot

about having the slide so self-re

extract here so in Beal translation they

mix different polymers together mix

amino acids and then they would measure

um the different poly pepid that formed

and which amino acids were in them this

um ribosome binding assay then was an

assay where they had a

ribosome okay they had a bunch of trnas

so here's a bunch of trnas all of which

or bound to different amino acids and

then they would give the system or put

in the system a specific codon all right

and so what happened in the system then

is the TRNA that matched that codon

would bind in the ribosome so what they

do is then they'd run all of that

through a filter okay and all the

Unbound trnas the tras that weren't

inside of the ribosome would flow

through the filter the ribosomes would

get caught on the filter

they then could detect what amino acid

was bound to that TRNA so basically a

one at a time type experiment they did

one codon then the next and the next so

they had to do all 64 codons and again

they knew what a lot of those would be

and so this verified all that and then

it solved um the few that they didn't

quite know at that point here's another

figure showing essentially the same

thing so here's the ribosome there's the

codon or tri-nucleotide um there's the

TRNA with an amino acid on it and it

runs through a filter and again you can

see the trnas go through the holes or

the pores in the filter where the

ribosome gets caught and then they can

detect what um amino acids on the TRNA

inside of that ribosome all right so

when all of a sudden done they sorted

out what um every single nucleate or

every single codon coded for what amino

acid was coded for by it and then

there's you can find this you find lots

of these on Google you just type in a

Code table and you find lots here's just

one example of it um and showing you all

the different different codons and then

next to it all the different amino acids

that are in it all right so what are

some of the uh characteristics then of

this uh genetic code so some of this be

repeat what I said a little bit earlier

um it is a tripet code okay and we just

talked about that the codon is made up

of three nucleotides three for triplet

it is continuous um didn't talk about

this explicitly but there's no skips or

jumps there's no periods no commas um it

reads each

three nucleotides it doesn't skip over

any of them as it's going um it's non

overlapping we talked about this earlier

each successive groups of three it

doesn't um it does this on the bottom

here three and then three and then three

it doesn't overlap does not do that all

right um it's I have Universal here it's

almost Universal almost all organisms

share the same code um there's again

it's biology so there are a few

exceptions mitochondria has a few

exceptions there's some organisms like a

protozoan has some um exceptions but

it's nearly Universal and that actually

allows scientists and research labs when

you're using model organisms to put

genes from one organism into another

organism and it works the same way um

the gentic code is said to be degenerate

and what that means is that there are

multiple codons that code for the same

amino acid all right so every amino acid

is coded for by at least one codon and

most of the amino acids are coded for by

multiple codons so if you look at the

genetic code table we can see that here

so here's Lucine these four nucleotides

code for lucing and addition Lucine

actually has two more nucleotides so six

different nucleotides code for Lucine

veine has four lots of them have four as

you can see in his whole row here some

of them only have a couple you know

alanine there spine Hine um see cine S2

tyrosine S2 gline S4 and arine S4 so um

different ones methine

however only has one and it also is a

special um codon it's called the start

codon because when protein when

translation starts protein synthesis

starts it always starts at an Aug okay

so there can be augs later in the

protein and so it's just a regular

methine you know get put in but it

always starts at Aug there are also

three codons that are called stop codons

originally they're called nonsense

codons because they didn't make any

sense they didn't bind to any

amino acid in any of the assays and and

didn't produce any um or didn't put any

amino acids in when these particular

codon showed up and then they realized

that they're stop codons and this is

what tells the the cell then to stop

translating and we'll see how that works

and we talk about the details of

translation all right so you have uh

stop signals those are the stop codons

which I just pointed out and the start

signal which is at aug okay so there's

specific Cod a specific codon for start

there are three different specific

codons for

stop all right so how do codons which we

just talked about interact with

anti-codons which we talked about when

we talked about the structure of trnas

that those three nucleotides on the uh

anti-codon loop of the TRNA interact

with the codon so the anti-codon of the

TRNA in a thre pre to five Prime order

matches or is complimentary to the codon

on the MRNA a 5 to3 Prime orientation so

again and and this is a good time to

talk about when base pairing occurs

between

nucleotide chains two two different

nucleotide strands whether it be DNA and

DNA making the double helix whether it's

RNA binding to DNA say when SI RNA binds

to RNA um or sorry that's RNA RNA or

when RNA binds a DNA say when an SN RNA

a snurp the RNA and a snurp binds to to

um an hn RNA um or in this case where

the codon anti-codons base pair it is

always went the base with the strands of

DNA in opposite orientations or

anti-parallel to one another okay they

are always anti-parallel that's how um

hydrogen bonding between bases takes

place so here is the MRNA 5 Prime 3

Prime and this isn't label on this side

but that means five Prime is on the C

end here three prime is on the the G end

here and for this TRNA a five Prime is

on the G end three prime is on the a end

okay it has to read from over here five

Prime to 3 Prime over here because mRNA

is five Prime to 3 Prime they have to be

anti- parallel okay so codon is on the

MRNA anti-codon on the TRNA um there's a

little bit of an exception to this um

base pairing the base pairing doesn't

always have to be all three nucleotides

there's something called wobble and

wobble occurs at the anti-codon five

Prime nucleotide okay or other said

otherwise the three prime nucleotide in

the

codon so the five Prime nucleotide of

the anti-codon does is not constrained

to bind as tightly many of the codons

that code for the same amino acids

differ at the three prime end um this

doesn't mean that any wobble occurs all

the time they're actually wobble rules

not all five Prim nucleotides of the

anti-codon can base pair with any three

prime nucleotides in the codon okay so

there's specific rules to this so um the

reason this works is for example here

with Lucine right as long as you bind

the C and the U it doesn't matter what

nucleotide is in this third spot C and U

is enough to code for locing so Proline

if you have CC doesn't matter what the

third nucleotide is it's still going to

code for Proline and so built in there

is some wobble um and for some and again

this is for all of the amino acids but

for some of them um it doesn't matter

what that third nucleotide is in the

codon um isoaccepting

trnas isoaccepting trnas are trnas that

accept the same amino acid but are

transcribed from different genes and

therefore have different anti-codons

okay so it's just another way saying

there's multiple trnas for any given uh

amino acid and this is because there's

multiple codons for any given amino acid

um I think I have a picture here the

wobble rules yeah so here it shows um

this TRNA caring phenol alanine has an A

A but it's able to recognize uuu so the

a and u a and u are correct base pairs

but G and U normally do not base pair

and if we go and look at uuu in the um

genetic code table here so uu is phenol

alanine

and u u c oops wrong one U uu or u u c

is phen alanine so a a will bind because

the wobble rules to uuu but it also bind

to UU C which is also pheno alanine so

our cells then can get away with having

a single TRNA a okay that has a a that

can bind to UU and uu C because of

wobble at this third position and again

there are rules so if the third base MRA

is a the base and anti-codon can

actually be quite a few different things

let's go to the simplest one if Third

Base m c you combine the G which is

normal you combine the a which is not

normal and I which is in aene one of

those modified bases so there are

certain restrictions to what the third

base

uh in sorry Third Base either in the

MRNA which is the first on the five

Prime and in the

TRNA all right so let's start talking

about the details of translation we've

been talking about details but let's

talk about how translation occurs so the

genetic message encoded by the MRNA is

translated in a five to3 Prime Direction

okay and the polypeptide is made in the

N Terminus to C Terminus Direction all

right so that's the colinearity the n

termin lines up with the five Prim Prime

end of the MRNA the C Terminus lines up

with the three prime end of the MRNA

ribosomes bind the MRNA and TRN carrying

amino acids are brought in each amino

acid binds to its own specific TRNA and

remember we talked about their

isoaccepting trnas and the codon on the

MRNA binds with the anti-codon on the

TRNA trnas are similarly shaped to fit

inside the ribos

they have sort of this L shaped in three

dimensions and you can see here here's

two different um tras one for phenoline

one for aspartate and they have this

similar upside down L shape okay so

they're slightly different if you look

at them closely um just a little bit

different but um they have the similar

shape and that's because they need to

fit in a similar um place inside of the

ribosome so the MRNA

or sorry the MRNA codon recognizes the

TRNA anti-codon the MRNA does not

recognize the amino acid bound to it and

scientists didn't know this initially so

they didn't experiment to figure it out

they want to know what is recognized by

the MRNA and to do this um they did

experiments where the amino acid bound

to the TRNA was chemically

changed so they had a TRNA that normally

carried cysteine here and they could

treat it chemically with nickel hydride

and change it to a TRNA that had the

anti-codon for cine but now was carrying

alanine so a

slide to show this so here's TRNA

carrying cysteine here so normally what

happens is if they gave it a ugc poly

ugc mRNA it would always put in 16 cine

so again inv vital translation

experiment but if they treated this with

nickel um it would change a cysteine to

an alanine so the TRNA still has the

anti-codon for cysteine but it's

carrying an alanine so they want to know

well is is the MRNA going to recognize

um this anticodon and put an alanine or

is it going to recognize this one and

put in Cy so it turns out that when they

did this used the

ugu this TRNA would still be recognized

because it had the cysteine anticodon

but it would put in alanine because that

had been changed so in other words the

MRNA has no idea what amino acid is

being carried on the TRNA it only

recognizes those three um nucleotides in

the

anti-codon all right so the process of

attaching an amino acid to its TRNA is

called charging the TRNA or amino

isolation a class of enzymes called

aminal ACL TRNA synthetases help charge

trnas there's at least one Amino ACL

TRNA synthetase for each amino acid it

recognizes the trna's anticodon in

sometimes other regions of the TRNA in

order to attach correct amino acid so

this sort of then answers the question

well how does a cell put the correct

amino acid on the correct TRNA or the

TRNA that has the correct anti-codon

these Amino ACL TRNA synthesises are

responsible for that recognition they

recognize the correct TR RNA with the

correct anti-codon and put the correct

amino acid on it or attach to that TRNA

an activated TRNA with its proper amino

acid attach is called an amino Amino ACL

TRNA or sometimes called a Charged TRNA

so charging a TRNA is a two-step process

that requires the hydrolysis of ATP and

so we'll talk about this in two steps

one is joining the amino acid to ATP and

the other then is transferring the amino

acid onto the

TRNA all right so I have steps one in

steps two and I have a couple sides to

look at as we look at this so in Step

One the amino acid and

ATP bind to the amino ACL TRNA

synthetase okay so you have the amino

acid here and you have ATP here they

will bind then to the Mr or to the TRNA

synthetase two phosphates are hydrolized

right it's from ATP it loses two

phosphates the leaves so two phosphates

are hydrolized from the ATP forming

bound to the amino acid all right so

this will be bone to the amino acid and

the correct TRNA binds the enzyme so

then the TRNA comes in and binds the

enzyme this step is required to make

step two energy favorable and step two

is the amino acid now is transferred

from

the to the

TRNA okay so the amino acid is

transferred for to TRNA which is then

released this step from the enzyme the

amino acid through its carboxy group is

attached to the two prime or thre Prime

hydroxy of the ribos sugar adenosine and

so see what that looks like here you've

seen this so you have the acceptor stem

here so you have the free three prime

Denine here and it's either going to be

attached to the two prime or the three

prime hydroxy to the carboxy group so

that's the little blue squiggly here is

the calent bond between the TRNA and the

amino

acid all right um this next side

probably shows these steps um a little

bit better so again step one your

specific amino acid

here ATP here they're both going to bind

to the amino ACL TR synthetase then

what's going to happen is the TP is

going to be hydrolized all right so two

phosphates are leave or pyrro phosphat

is going to leave that provides the

energy then to Coal link a Denine

monophosphate to the specific amino acid

then the T specific TRNA is going to

bind to the amino ACL TR synthetase the

energy then this bond is going to be

broken between the phosphate and the

amino acid that energy is going to be

transferred to form the calent bond

between the TRNA and the amino acid and

then the amino Amino AAL TRNA synthetase

is going to release the charged or amino

isolated TRNA so this side if you're

going to study this is probably the

better side it shows the steps more

explicitly than that previous side that

I started with um this side here shows a

little bit better look at um how the

amino a acid is um cently linked so

here's anticodon it just flipped from

the direction the other ones we looked

at so

CC phosphate and a all right and five

Prime here so one prime two prime three

prime so you have the two prime hydroxy

and the three prime hydroxy here um and

the amino acid could be linked to either

this one shows the amino acid linked to

the three prime hydroxy group so that o

belong to ribos and see o carboxy group

here there is a calent bond and again a

molecule water is released and forming

that calent

Bond so that's how amino acids get on

trnas a cell actively carrying out

protein synthesis will have a large

number of charged or amino isolated

trnas floating around in the cytoplasm

waiting to participate in protein

synthesis all right ribosomes um another

major part that is involved in

translation ribosomes are the location

for protein synthesis the MRNA and trnas

must fit into the ribosome to carry out

this function the MRNA is completely in

the small subunit so where are these

things the MRNA is completely within the

small subunit the anti-codon of the TRNA

is also in the small subunit and the

TRNA Bridges the small and large subunit

with the amino acid in the large subunit

um when the ribosomes come together well

so anticodon also in the small subunit

TR um spans large and small and amino

acid then is in the large subunit so

when the ribosome comes together then it

creates different sites known as a p and

E site the a site or aminal ACL site is

the site that binds the incoming TRNA or

the amino isolated or charged TRNA as it

comes in that is the aite the pite or

pepal P stands for pepal contains a TRNA

that holds on to the growing peptide

chain so as peptide chain grows it's

always linked to a TRNA and that TRNA

resides in the psite the eite stands for

exit contains the deated TRNA as it is

released so as the TRNA

transfers the growing peptide that is on

it it will then release through the exit

site so we can take a look at some of

this here so um image up here just shows

an mRNA and a bunch of ribosomes on it

okay and the green is the growing amino

acid coming off it so um an mRNA can be

used multiple times by multiple

ribosomes to make multiple polypeptides

all right so it's not a one shot deal

just um uh an x-ray model of ribosome

and down here is ribosome and in the

next slide I've enlarged that a little

bit so you can see a little bit better

here um so here you go e p a sites so

here's the MRNA it's in the small

subunit site TRNA is going to interact

or the anti coding interact in small

subun TRNA going to span large and small

polypeptide and amino acid that's linked

to the TRNA is going to then in the

large subunit so a is where the TRNA is

going to come in that has a single amino

acid P then is the TRNA now as you can

see with the growing polypeptide once

this polypeptide is transferred over and

we'll go through these steps this deated

TRNA will go to the eite and exit out of

the

ribosome um it's another model showing

similar thing shows actually the a site

being occupied by a TRNA with an amino

acid on it and a P with a growing

polypeptide and the exit site where the

last de isolated TRNA had just

left all right so now we'll start

getting into the details of translation

translation can be divided into three

stages or steps we have initiation

elongation and termination very similar

to transcription having three steps

we'll do the same thing here for

translation um so initiation in involves

binding of the MRNA to the small rabal

subunit that's number one binding of the

initiation TRNA to the small ribosomal

subunit and binding of the large

ribosomal subunit to the small subunit

so there's a number of steps in

initiation and um so just a little bit

of introduction we'll end this portion

here and we'll start with the steps in

the next um lecture