Topic 8: RNA Structure and Transcription

Summary

Este video analiza el dogma central de la biología, que explica cómo el ADN se convierte en proteínas a través de dos procesos: transcripción y traducción. La transcripción ocurre en el núcleo, donde el ADN se copia en ARN mensajero (ARNm), y la traducción sucede en el citoplasma, donde el ARNm se convierte en proteínas. Se explican las diferencias entre el ADN y el ARN, así como los tipos de ARN involucrados en este proceso. Además, se introduce la regulación de la expresión génica, destacando los factores que influyen en la transcripción y cómo se procesan los intrones y exones en el ARN.

Takeaways

• 🧬 El dogma central explica cómo el ADN se convierte en proteínas mediante dos procesos: transcripción y traducción.
• 📜 La transcripción ocurre en el núcleo y convierte ADN en ARN mensajero (ARNm).
• 🔄 La traducción ocurre en el citoplasma y convierte el ARNm en proteínas.
• 🔬 El ARN es un ácido nucleico que actúa como intermediario en la producción de proteínas.
• 🌐 El ARN tiene uracilo en lugar de timina, lo que lo diferencia del ADN.
• 🧩 En la transcripción, el ARN mensajero se empareja con bases complementarias del ADN: G con C, A con U.
• 🚶‍♂️ La transcripción tiene tres etapas: iniciación, elongación y terminación.
• 🔗 La ARN polimerasa es responsable de desenrollar el ADN y formar el ARNm.
• ✂️ Los intrones se eliminan y los exones salen del núcleo para convertirse en ARNm maduro.
• ⏳ La degradación del ARNm regula la expresión genética, ya que afecta cuánto tiempo se traduce en proteínas.

Q & A

¿Qué es la dogma central de la biología molecular?

La dogma central de la biología molecular explica cómo el ADN se convierte en proteínas a través de dos procesos: la transcripción (ADN a ARN) y la traducción (ARN a proteínas).

¿Dónde ocurren la transcripción y la traducción en la célula?

La transcripción ocurre en el núcleo, mientras que la traducción ocurre en el citoplasma.

¿Cuál es la principal diferencia entre ADN y ARN?

El ADN contiene desoxirribonucleótidos y tiene timina como base, mientras que el ARN contiene ribonucleótidos y usa uracilo en lugar de timina.

¿Qué es el ARN mensajero (mRNA) y cuál es su función?

El ARN mensajero (mRNA) es una molécula intermedia que transporta la información genética del ADN al ribosoma para la síntesis de proteínas.

¿Qué son los intrones y exones en el proceso de transcripción?

Los intrones son secuencias no codificantes que se eliminan del ARN antes de que este salga del núcleo, mientras que los exones son las secuencias que permanecen y codifican para proteínas.

¿Qué papel juega la ARN polimerasa en la transcripción?

La ARN polimerasa es la enzima responsable de unir y copiar la hebra de ADN en ARN durante la transcripción, tanto desenrollando el ADN como haciendo el apareamiento de bases complementarias.

¿Qué es el proceso de iniciación en la transcripción?

La iniciación es el primer paso de la transcripción en el cual la ARN polimerasa se une a una región promotora en el ADN para comenzar a sintetizar ARN.

¿Qué sucede durante el proceso de elongación en la transcripción?

Durante la elongación, la ARN polimerasa se desplaza a lo largo del ADN y sintetiza una cadena de ARN utilizando el apareamiento de bases complementarias.

¿Qué ocurre en la etapa de terminación de la transcripción?

En la terminación, la ARN polimerasa llega a una secuencia de terminador en el ADN, lo que hace que se detenga la transcripción y se libere el ARN recién sintetizado.

¿Cómo se procesa el ARN antes de salir del núcleo?

El ARN recién transcrito se somete a un procesamiento que incluye la adición de un caperuza en el extremo 5', una cola poli-A en el extremo 3' y la eliminación de intrones, dejando solo los exones.

¿Qué es la traducción y dónde ocurre?

La traducción es el proceso por el cual el mRNA se utiliza para sintetizar proteínas. Ocurre en el citoplasma, específicamente en los ribosomas.

Outlines

00:00

🧬 Central Dogma y Proceso de Transcripción

El primer párrafo explica el concepto de la Dogma Central, que describe cómo el ADN se traduce en proteínas. Se mencionan dos procesos principales: Transcripción (de ADN a ARN) y Traducción (de ARN a proteína). La Transcripción ocurre en el núcleo y la Traducción en el citoplasma. Se destaca la importancia de los genes como regiones específicas del cromosoma que codifican proteínas. Se explica la diferencia entre ADN y ARN, destacando que el ARN es una molécula intermedia que lleva la información proteica y puede catalizar algunas reacciones. Se presentan los tipos de ARN: mensajero (mRNA), de transferencia (tRNA) y de la ribosoma (rRNA).

05:00

🍪 Genes como Recetas y Proceso de Transcripción

El segundo párrafo compara los genes con recetas, explicando cómo cada gen se puede considerar una receta para producir una proteína específica. Se describe el proceso de Transcripción como la fotocopia de una receta para no dañarla. Se menciona que, al igual que las recetas, solo se transfiere una parte del ADN (el gen) a ARN para su posterior traducción a proteínas. Se enfatiza la importancia de la Transcripción como el paso intermedio entre el ADN y las proteínas, y cómo la secuencia de bases en el ADN determina la secuencia en el ARN.

10:01

🔬 Detalles del Proceso de Transcripción

En el tercer párrafo se explican los detalles del proceso de Transcripción, que incluyen la iniciación, la elongación y la terminación. Se describe la función de la RNA polimerasa, que actúa como un enzima promotor y catalizador del proceso. Se menciona la importancia de la región promotora en el inicio de la Transcripción y cómo solo una cadena del ADN se utiliza como plantilla para la síntesis del ARN. Se aborda la terminación del proceso cuando se alcanza la secuencia terminadora, despidiendo la RNA polimerasa y liberando el ARN completo.

15:02

🧬 Regulación de la Expresión Genética

El cuarto párrafo trata sobre la regulación de la expresión génica, que comienza en el núcleo de las células eucariontes. Se describe cómo ciertos genes están compactados y no pueden ser transcritos, mientras que otros están disponibles. Se explica el proceso de maduración del ARN mensajero, incluyendo la eliminación de intrones y la formación de exones, lo cual permite que el ARN salga del núcleo y se traduzca en proteínas. Se mencionan los factores de transcripción que ayudan a regular la expresión génica y la importancia de la esplicación alternativa para crear diferentes proteínas a partir del mismo ARN.

20:03

🌐 Regulación de la Expresión Genética y Proceso de Traducción

El quinto párrafo profundiza en la regulación de la expresión génica, mencionando mecanismos como la retención del ARN mensajero en el núcleo y la degradación del ARN. Se discute cómo la actividad de las proteínas y su capacidad de ser correctamente doblegadas y ubicadas también influyen en la expresión génica. Se hace una revisión del proceso de Transcripción y se establece la conexión con el proceso de Traducción, que es el siguiente paso en la conversión del ARN mensajero en proteínas.

25:03

➡️ Proceso de Traducción y Función del ARN

El sexto párrafo concluye el video explicando cómo el ARN mensajero, una vez procesado y maduro, se dirige al citoplasma para iniciar la Traducción. Se describe cómo el ARN se une a la ribosoma y se traduce en una cadena de aminoácidos que formará la proteína. Se enfatiza la importancia de que el ARN esté listo para la Traducción y cómo los intrones son eliminados para que solo queden los exones, que especifican los aminoácidos.

Keywords

💡Dogma central

El dogma central describe el flujo de información genética desde el ADN hasta las proteínas. Este concepto central se refiere a los dos procesos clave: la transcripción (de ADN a ARN mensajero) y la traducción (de ARN mensajero a proteína). En el video, se menciona como el mecanismo principal que explica cómo la información genética en el ADN se convierte en las proteínas necesarias para las funciones celulares.

💡Transcripción

La transcripción es el proceso mediante el cual el ADN se convierte en ARN mensajero (ARNm). Ocurre en el núcleo y es esencial porque permite que la información genética del ADN se convierta en un formato que pueda ser utilizado para producir proteínas. En el video, se enfatiza que la transcripción es una de las dos fases principales del dogma central.

💡Traducción

La traducción es el proceso por el cual el ARNm se convierte en una proteína en el citoplasma. Esta es la segunda etapa del dogma central, donde el ARNm guía la producción de proteínas específicas. El video explica cómo la traducción ocurre en los ribosomas y es crucial para la síntesis de proteínas.

💡ARN mensajero (ARNm)

El ARNm es una molécula intermedia que lleva la información codificada en el ADN al ribosoma para la síntesis de proteínas. En el video, se menciona como el producto de la transcripción y la clave para transportar la 'receta genética' desde el núcleo hasta el citoplasma, donde se realizan las proteínas.

💡ARN de transferencia (ARNt)

El ARNt es una molécula que lleva los aminoácidos necesarios para construir proteínas durante la traducción. El video explica cómo el ARNt juega un papel esencial en la segunda fase del dogma central, transportando los aminoácidos al ribosoma para formar la cadena proteica.

💡Promotor

El promotor es una región del ADN que señala el inicio de la transcripción al ARN polimerasa, la enzima encargada de sintetizar el ARN. En el video, se utiliza una metáfora donde se compara con un 'promotor' que inicia la carrera de un artista, en este caso, iniciando la producción del ARN.

💡ARN polimerasa

La ARN polimerasa es la enzima responsable de copiar la secuencia de ADN en ARN durante la transcripción. En el video, se menciona como la enzima clave que no solo sintetiza ARN, sino que también desenrolla el ADN, combinando dos funciones en una sola enzima.

💡Exón

Los exones son las partes del ARN que codifican información para la síntesis de proteínas y que se mantienen en el ARN maduro tras el procesamiento. En el video, se explica que estos exones 'salen' del núcleo y se traducen en proteínas, mientras que los intrones se eliminan.

💡Intrón

Los intrones son las secuencias no codificantes del ARN que se eliminan durante el procesamiento antes de que el ARN maduro sea traducido en proteínas. En el video, se compara el proceso de eliminación de intrones con limpiar la información no necesaria para producir una proteína funcional.

💡Cap y cola poli-A

La cap (caperuza) y la cola poli-A son modificaciones químicas añadidas al ARN mensajero maduro para protegerlo y facilitar su salida del núcleo hacia el citoplasma. En el video, se explica que estas modificaciones ayudan a evitar la degradación del ARNm una vez que se encuentra en el citoplasma, asegurando su estabilidad durante la traducción.

Highlights

Introduction to the central dogma of molecular biology and its two processes: transcription and translation.

Explanation of where transcription and translation occur within a cell.

Description of the role of DNA and genes in protein production.

Differences between DNA and RNA, including the sugar component and base pairing.

The function of RNA in protein synthesis and its three types: mRNA, tRNA, and rRNA.

Analogy of genes to recipes in a cookbook, explaining gene expression.

Process of transcription from DNA to messenger RNA (mRNA).

The three steps of transcription: initiation, elongation, and termination.

Role of RNA polymerase in the initiation of transcription.

Mechanism of elongation in transcription where RNA polymerase synthesizes RNA.

Termination of transcription and the release of mRNA.

Gene regulation starting in the nucleus and its impact on gene expression.

Difference between prokaryotic and eukaryotic cells in terms of transcription and translation.

Importance of RNA processing, including the removal of introns and addition of a cap and tail.

The role of transcription factors in regulating gene expression.

Differentiation between exons and introns and their role in mature mRNA formation.

Regulation of gene expression through RNA export and degradation.

Importance of protein folding and stability in gene expression.

Overview of the transcription process and its significance in gene expression.

Transcripts

foreign

hi everybody so as you remember this is

going to be the second part of this

discussion and we are going to actually

dig into the central dogma which again

explains how DNA is encoded into

proteins

as a reminder there are two processes

processes to the central dogma the first

one is when DNA goes to RNA specifically

we're going to look at messenger RNA and

this is called trans

description

and the second part taking messenger and

RNA to protein is called translation

transcription happens in the nucleus

translation happens in the cytoplasm

so protein production always starts with

DNA and what it essentially starts with

is a gene that is a small region of

amdna that's in part of a chromosome

right the sequence of DNA in each gene

is what's going to encode or be the

specific protein that we make

so in order for proteins to be produced

it requires this kind of intermediate

molecule called RNA RNA is a nuclear

nucleic acid as a review from what we

looked at at the beginning of the

semester when we looked at biomolecules

but how are they different from DNA well

a big part if you look here are

the areas on the bottom and when we're

talking about five Prime three prime

we're looking at this is a very first

carbon because this is where the base

would be attached if we add the sugar so

that's one that's two that's three four

and five

so on the second one you'll notice in

DNA it's called deoxy

ribonucleic acid because d means it's

without an oxygen which is there

so that's one way that it's different

right and when we talked about three

prime I said when you looked at 3 Prime

there's always a hydrogen is the last

atom well it's true but if you look at

it it's fully the o h that's there at

the end and then essentially what will

happen up here is you'll get that

phosphate that's there

so when we look at the sugar that's the

difference on the sugar now a big thing

that we'll notice and you can easily

tell for sequence of an RNA if you have

DNA or RNA because if you have DNA you

have thymine

and if you have RNA you have uracil

so when we look at this G's and C's

still base pair with each other but

anywhere you have a t you would now have

a u in your messenger or name

so if you have a DNA sequence this is

our DNA

that has c g t and a

your messenger RNA

would then be still G

it would be C where T is it would be a

but where a is it would now be U

so you can put this together the same

way as you do your complementary DNA

sequence it's just wherever you would

have a t you'd replace it with a u

now that makes a big difference in terms

of what we have here because what we

have if you look

here messenger RNA tends to be single

stranded and then DNA we know it's

double-stranded

and it also is different in its function

so it encodes in DNA storage for RNA and

protein encoding information and

transfers information to next generation

of cells or RNA carries protein accorded

information and helps to make proteins

specifically it even can catalyze some

reactions

so there are three types of RNA

we have messenger RNA which is when we

look at the central dogma that's where

we go DNA

2 RNA

Transfer RNA is going to be what helps

to make

RNA

2 protein

so it's going to be what actually helps

carry the information or carry the amino

acids to make the protein

and there are RNA that's part of the

ribosome specifically

and this is where translation is going

to occur so there are different types of

RNA molecules and shorthand for

Messenger rnas mRNA for transfer rna's

TRNA and for ribosomal it's RNA there

are other types of RNA but that is for a

more advanced class to discuss those

so I like to think about genes being

like a recipe in a good cookbook and

when I talked about this earlier in the

semester I compared it to my mom's

recipes

my mom was a fantastic cooking Baker I

grew up as a child on a farm

in Iowa we didn't have a whole lot of

money so my mom made everything from

scratch so when she passed away from

cancer it was really really important

that I get something that I felt was

what reminded me of her a part of her

and that I really identified with so I

took all her recipe boxes and everything

so all her recipe boxes in her big

recipe box has these individual recipe

cards

so the whole box itself

would be like this cookbook here oops

it has every single recipe that she ever

made kind of consistently that she

didn't have stored in her brain right

just like this cookbook does it has

multiple recipes in it so that would be

like our chromosome with a lot of genes

on it but we don't want to cook the

entire recipe in the box or all the cook

recipes in the cookbook we only want to

make brownies so we're going to take out

one recipe and then we are going to make

a photocopy of that

now I think about in terms of my mom's

box

I don't want to I don't like really

cooking with them because I'm scared I'm

gonna mess them up and once I mess them

up they're gone forever and they make so

much they're very very

um close and dear to me because a lot of

them are handwritten by her and so it

makes me feel extremely close so I

wouldn't want anything to go wrong with

it so I like to make copies of them

so this is what it's showing here is

that copy of that one brownie recipe

right the great thing is is if I make a

copy of it and I decide not to make the

recipe I can throw it away it's no big

deal

so if there are signals that say I need

to make this protein but then ends up

being so that we don't need to

necessarily make it the bot the cell

will just destroy it and it's no loss

right because we have the original

recipe or Gene still in the nucleus

now when we want to make that brownie

recipe we have to basically put things

like flour and sugar and salt and cocoa

and butter and eggs

all of those individual things would be

like the amino acids that we're using

here

4r

protein so we're going to bring all

those different amino acids make our

batter and cook it and so when we

actually get our protein

ready or you know done that's equivalent

to having our brownies ready to be eaten

or used however we need to

so the process of making the photocopy

because we stay in the same language is

transcription and the process of taking

that photocopy and making it actually

into our brownies is translation

foreign

is a process of taking DNA and creating

RNA

and so um

basically with DNA going to messenger

RNA we are staying in the same type of

biomolecule which is a nucleic acid

so what I want you to do here and you

can see in the description below that

there is a video and you you're just

going to watch this and it's going to

take you through the central dogma

overview what we're going to talk all

the way from DNA to protein but what

we're going to focus on next after you

watch this to get an idea what we're

about to talk about

is

transcription

so in transcription DNA sequences

determine the RNA sequence so when we

want to make RNA what I was talking

about earlier base pairing takes place

between the RNA and the DNA molecule

and we use complementary base pairing

oh if we look we do complementary base

pairing

basically if we have a piece of DNA that

has a c g and T as we know if we were

doing another piece

of DNA here

the complementary base pairing would be

t

n 4 C right G and four g c and four

thymine a those would be the DNA

complementary base pairing

now when we go to take DNA

and we base per with RNA we get you for

your cell C still base pairs with G that

doesn't change from what we saw here

G still base pairs with C and thymines

still base pairs with adenine so

basically we just replace

all RTS n d and hay

with use for RNA

and basically these if we go through and

make base pairing RNA to RNA

we follow the same rules that we did

from when we went from DNA to RNA as you

can see we already have uracil in our um

in our RNA there so it will base pair

with adenine

and here again adenine will base pair

with uracil

now that's base pairing how do we make

this messenger RNA to begin with

well there are three steps that take

place initiation

elongation and termination

so let's talk about each one of these

so in transcription initiation RNA

polymerase gets started as you remember

enzymes always tell us what we do so it

starts it ends with an ace that's how we

know what essentially

um

we have an enzyme and then it's telling

us what it makes which is RNA polymer

right so in if you remember when we were

in DNA replication we had DNA polymerase

because it was making a DNA polymer

so what happens here

is here

is the gene we want to make

now just like if you are a you know

someone who's new in the music field you

want your career to get started you want

people to know you and get everything

like maybe you want to get things booked

right venues

um get on the TV get on the radio so you

hire a promoter to basically get your

career started so think about this we

have what's known as the very first area

here a promoter region

and this is where our enzyme

will bind

to start

transcription which makes sense we're

starting transcription right because

we're at initiation

so we're starting the process

right

so basically this is the area on the

gene the promoter region that RNA

polymerase will bind

there are things like transcription

factors

that help with this binding

so this is initiation in part one

now for initiation remember that the DNA

is always the template to start this but

only one strand will become or be used

as the template strand to make messenger

RNA

the other strand does not participate at

all

the second part of this is elongation

so think about it we are

making

a long

strand

of RNA

so this is where the RNA polymerase is

actually making

that's what synthesize means making

the RNA

so the RNA polymerase is going to move

along the piece of DNA using

complementary base pairing to do this so

if you remember from DNA replication you

had two enzymes

you had an enzyme called helicase

to unzip

and then you had DNA

polymerase

to make DNA strand

here

the RNA polymerase

does both

it unzips

the strand of DNA and then it does the

base pairing

so he's very efficient

so we do have this base pairing of

nucleotides that come in to make this

new

um strain of

RNA

the third step we have is termination

and if you get terminated from a job

you're basically getting fired so you

stop working there

that's what happens here the RNA will

reach the end

there is a Terminator sequence

that tells

the RNA polymerase

to stop

and once it reaches that end of the gene

it stops it falls off

once that termination happens the

messenger RNA is complete

at that at the Terminator sequence

the RNA the DNA the RNA polymerase they

all separate from each other the DNA

becomes a double helix again

so this the cell is actually produced an

RNA copy of that Gene

now the overall expression of those

genes is going to be what it makes at

the end but the way that DNA in packaged

regulates gene expression

so when eukaryotic cells our cells for

instance Gene regulation actually starts

in the nucleus

some genes are wound up so tight they

can't be transcribed but other genes are

available

and what's cool is once you get that

messenger RNA remember how I said you

can't leave your house until you're

mature

well they're going to go through a

process

that removes pieces of RNA that doesn't

need to be there

and it's going to allow only those

pieces of RNA

to actually leave so if you notice

there's two types there are what called

exons and introns

introns

get removed and stay in

the nucleus

Excellence exit

the nucleus and become what's known as

mature messenger RNA and it's going to

move out of those nuclear pores

to the cytoplasm

and as I also um said about starting

transcription you have or what are known

as transcription factors and they help

to regulate gene expression too

in eukaryotic cells many different

proteins that are called transcription

factors combined to DNA and help with

the process of transcription being

turned on

this is going to affect the activity of

RNA polymerase altering the rate of

transcription

in eukaryotic cells they can use

different combinations of what are

called exons this is what's known as

alternate splicing and this creates

different proteins from the same

messenger RNA

so you can see here the introns get cut

out and stay in

they really get

um deteriorated

and then the exons exit

and they become the actual messenger RNA

that will be translated to a protein

you also have the process of RNA export

that regulates gene expression so

certain eukaryotic proteins can actually

hold messenger RNA inside the nucleus

making it so that it can never reach a

ribosome so that will also determine

whether or not a Gene gets expressed or

made into a protein

ornate degradation can also regulate

gene expression degradation means

breaking down

so when that messenger RNA exits the

nucleus and goes into the cytoplasm

right that's where it is now

some messenger RNA may be broken down to

graded very quickly so they can't be

translated into very much protein or

protein at all other messenger rnas are

long-lived and can be translated into a

lot of protein over time so depending on

your genes it can either

um

be translated for a long time or short

amount of time based on RNA degradation

protein activity can also regulate gene

expression some proteins are more stable

why others are broken down quickly

moreover in order to function proteins

must also be folded properly and reach

the correct location so we were talking

about the Philadelphia in mad cow

disease and as you know and what we'll

talk about later in this talk is an idea

of prions but first in order for us to

understand what a prion is we have to

know what a protein is and how proteins

are made but as I always say for

instance I have a shirt on right now it

has a hole at the top so I can put my

head in it it has two holes so that my

hands and my arms can go through it it

has a large hole at the bottom so my

torso can fit now I could have this

shirt made but if the hole where my head

goes through isn't there

it's not gonna work as a shirt

so if proteins aren't put together

correctly I.E folded right they won't

work right

so this is one important thing that we

will talk about

so let's review transcription really

quick and you can take some important

notes on the things that you feel are

the most important in the process and

remember it is in three steps initiation

elongation

and termination that's how I remembered

them and this will give you an idea of

how this works overall

and this will lead us to

the idea of RNA processing

and basically one more step in order for

the RNA

to leave the nucleus once transcription

is complete

it needs to be processed to become

mature

one of those is the introns and exons

so if you think prokaryotic cells

everything happens in the cytoplasm they

don't have a nucleus

so as once transcription is complete

they will start translating protein now

they can actually have it happen at the

same time as in

the process of transcription could be

happening in as it transcribes the DNA

at the areas that have already been made

to messenger RNA you can start

translation on it's pretty cool but

eukaryotic cells all of this is

happening in the nucleus so there has to

be chemical alterations that happen

before the messenger RNA can actually

leave for a translation to start

and one important process is adding a

cap and a tail to the messenger RNA

so as you notice the five primary that

had that phosphate they're going to add

this little structure that's called the

cap and then on the three prime they're

going to add what's called a poly a tail

and if you remember if you've ever heard

of anything called polyamorous

relationships versus monogamous

relationships monogamous starting with

mono means one

polyamorous means many people in a

relationship so polyatil just means

there's a lot of A's at the end and this

cap and a tail is going to protect the

messenger RNA from being broken down

once it goes into the cytoplasm

also we remove introns and the exons

become the sequence that's going to

specify the amino acids

and the introns are sequences in the

gene that aren't used for producing a

protein

so the introns are removed before it

leaves the nucleus

both of these allow the RNA to be ready

for translation or become mature

this processed RNA is now a functional

messenger RNA molecule

once it's completed that processing it

leaves the nucleus and then it will bind

to a ribosome in the cytoplasm for

translation to begin

and this is where we're going to stop

for this video so that you can

kind of review your notes look at

transcription and when we start here in

a minute we're going to talk about

translation and translation is we finish

this right

and now we're starting this

which is the process of taking messenger

RNA to proteins this is happening in the

cytoplasm in the messenger RNA is the

messenger from the nucleus on how that's

to happen