MK Biologi Molekuler - Regulasi Ekspresi Gen Prokariota

Summary

This educational video script delves into gene expression regulation in prokaryotes. It explains that genetic material in prokaryotes is typically concentrated in a specific region called the nucleoid and can also be found in circular, double-stranded DNA molecules known as chromosomes. The script outlines two main mechanisms of gene expression: feedback inhibition, which halts expression when product levels are sufficient, and gene regulation, which controls expression through transcription. It introduces the concept of the operon, a group of genes controlled by a shared promoter, and discusses how operons are regulated by repressors and inducers. The script uses the lactose (lac) operon and tryptophan (trp) operon as examples to illustrate negative and positive regulation, respectively, highlighting the importance of these processes in adapting to environmental changes.

Takeaways

• 🧬 Prokaryotic genetic material is concentrated in a specific area called the nucleoid and also in circular double-stranded DNA molecules known as chromosomes.
• 🔄 Bacterial chromosomes are unique in that they lack histone proteins and can be attached to the plasma membrane at a specific point.
• 🌟 The E. coli DNA contains 4,288 genes organized into 2,584 operons, including genes for ribosomal RNA and transfer RNA.
• 🔄 Gene expression in prokaryotes can be regulated through feedback inhibition, where the production of a gene product is halted when it is in excess.
• 🔑 The operon model is a key regulatory system in prokaryotes, where genes are activated or deactivated together based on the presence of a promoter and an operator.
• 🔒 The repressor protein plays a crucial role in the operon system by binding to the operator to block RNA polymerase, thus controlling gene transcription.
• 🔄 Inducible operons, like the lactose (lac) operon, are activated only in the presence of specific inducers, such as allolactose, and are involved in the metabolism of lactose.
• 🔑 The CAP (catabolite activator protein) acts as a sensor for glucose levels and influences the transcription of operons like the lac operon when glucose is scarce.
• 🔄 The trp operon is an example of a repressible operon that is regulated by the presence of tryptophan, which binds to the repressor protein and inhibits transcription.
• 📉 Negative regulation in prokaryotes involves the constant repression of certain genes, which can be relieved under specific conditions, such as the presence of inducers.
• 📈 Positive regulation, on the other hand, involves the activation of gene expression under certain conditions, such as when a cell prefers to use lactose over glucose due to limited glucose availability.

Q & A

What is the location of genetic material in prokaryotes?

In prokaryotes, genetic material is typically concentrated in a specific area of the cytoplasm known as the nucleoid. Additionally, genetic material can also be found in the bacterial chromosome.

What is the structure of the bacterial chromosome?

The bacterial chromosome is a single, circular double-stranded DNA molecule that is partially attached to the plasma membrane at a specific point.

How does the absence of histone proteins in prokaryotic DNA differ from eukaryotic DNA?

Prokaryotic DNA does not contain histone proteins, which is a key difference from eukaryotic DNA where histones help package and organize the DNA.

What are the two main types of gene expression regulation mechanisms in prokaryotes?

The two main types of gene expression regulation mechanisms in prokaryotes are feedback inhibition and gene regulation through operons.

How does feedback inhibition regulate gene expression in prokaryotes?

Feedback inhibition stops the expression of a gene when the product of that gene is in sufficient quantity, ensuring that the gene is only expressed when the product is needed.

What is an operon and how does it relate to gene regulation in prokaryotes?

An operon is a group of genes that are located close together on the chromosome and are controlled by a common promoter. They are activated or deactivated together, and they include structural genes, a promoter, and an operator.

What are the components of an operon?

The components of an operon include a promoter, an operator, structural genes, and a repressor protein.

How does the lac operon regulate gene expression in response to lactose and glucose levels?

The lac operon is regulated by the presence of lactose and glucose. It is induced when lactose is present and glucose is absent. The repressor (LacI) and the activator protein (CAP) control the operon's activity based on the levels of these sugars.

What is the role of allolactose in the regulation of the lac operon?

Allolactose is an inducer that binds to the repressor protein, causing it to change shape and no longer bind to the operator, allowing RNA polymerase to bind to the promoter and initiate transcription.

How does the trp operon regulate the biosynthesis of tryptophan?

The trp operon regulates the biosynthesis of tryptophan through a negative feedback mechanism. When tryptophan levels are high, it binds to the repressor protein, which then binds to the operator and blocks the RNA polymerase from binding, thus inhibiting transcription.

What are the two types of gene regulation in prokaryotes mentioned in the script?

The two types of gene regulation in prokaryotes mentioned are negative regulation, where gene expression is usually active but can be inhibited, and positive regulation, where gene expression is usually inactive but can be activated by specific inducers.

Outlines

00:00

🧬 Prokaryotic Genetic Material and Gene Expression

This paragraph discusses the concentration of genetic material in prokaryotes, typically in a specific area of the cytoplasm known as the nucleoid. Prokaryotic genetic material is also found in circular, double-stranded DNA molecules called chromosomes that partially attach to the plasma membrane at a point. Unlike eukaryotes, these chromosomes do not contain histone proteins. The script provides an example of Escherichia coli DNA, which is a single circular molecule containing 4.6 million base pairs and 4,288 proteins. It is organized into 2,584 operons, including seven operons for ribosomal RNA and 86 transfer RNAs. Many bacteria also carry extrachromosomal genetic elements in the form of small, circular, double-stranded DNA molecules called plasmids. The paragraph also explains two mechanisms of gene expression in prokaryotes: feedback inhibition, where gene expression stops when the product is sufficient, and gene regulation, where genes are expressed only when needed, typically through transcription control.

05:01

🔬 Operon Regulation in Prokaryotes

The second paragraph delves into the concept of operons in prokaryotes, which are groups of genes that are closely located on the chromosome and are controlled together, sharing a common promoter. It describes the components of an operon, including the promoter, operator, repressor protein, and structural genes. The promoter is where RNA polymerase binds, and the operator controls the activation of transcription. The repressor protein can bind to the operator to block RNA polymerase, thus stopping transcription. The paragraph also discusses the role of inducers, which can remove the repressor from the operator, allowing the operon to become active. An example given is the lactose (lac) operon in E. coli, which contains genes involved in lactose metabolism. The lac operon is only expressed when lactose is present and glucose is absent. The repressor (lacI) and the activator (CAP) work together to control the operon's activity based on the levels of lactose and glucose. The paragraph also mentions the trp operon, which contains genes for synthesizing tryptophan and is regulated by a repressor protein that is activated by binding tryptophan, inhibiting the operon's transcription when tryptophan levels are high.

10:01

🛠 Negative and Positive Regulation of Gene Expression

The final paragraph summarizes the two main types of gene expression regulation in prokaryotes: negative and positive regulation. Negative regulation refers to the repression of gene expression under normal conditions, which can be relieved when necessary, such as in the trp operon where tryptophan inhibits its own production when levels are high. Positive regulation, on the other hand, involves the activation of gene expression in response to specific signals, as seen in the lac operon where the presence of lactose and low glucose levels activate the operon through the binding of allolactose and CAP to the repressor and activator proteins, respectively. The paragraph emphasizes the importance of understanding these regulatory mechanisms for metabolic pathways in prokaryotes.

Keywords

💡Prokaryota

Prokaryotes are unicellular organisms that lack a membrane-bound nucleus or any other membrane-bound organelles. They are simple in structure and include bacteria and archaea. In the context of the video, prokaryotes are discussed as organisms with genetic material concentrated in a specific region called the nucleoid and also found in circular, double-stranded DNA molecules known as plasmids.

💡Nucleoid

The nucleoid is a region within a prokaryotic cell that contains all or most of the genetic material. Unlike the nucleus in eukaryotic cells, the nucleoid is not enclosed by a membrane. It is mentioned in the script as the specific location where genetic material is concentrated in prokaryotes, highlighting its role in gene expression regulation.

💡Chromosome

In prokaryotes, a chromosome refers to a single, circular, double-stranded DNA molecule that is often attached to the plasma membrane at a specific point. The video explains that unlike eukaryotic chromosomes, prokaryotic chromosomes do not contain histone proteins, which are involved in packaging DNA in eukaryotes.

💡Gene Expression

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product, typically a protein. The video discusses how gene expression in prokaryotes can be regulated through mechanisms such as feedback inhibition and gene regulation, which are crucial for controlling when and how genes are expressed.

💡Feedback Inhibition

Feedback inhibition is a regulatory mechanism where the end product of a biosynthetic pathway inhibits an earlier step in the same pathway. The video uses this term to explain how the expression of genes can be halted when their products are in excess, ensuring that the cell does not waste resources on unnecessary protein synthesis.

💡Operon

An operon is a unit of DNA that includes a set of genes under the control of a single regulatory element. In the video, operons are described as clusters of genes that are transcribed together and are controlled by a common promoter, which is crucial for coordinated gene expression in prokaryotes.

💡Promoter

A promoter is a DNA sequence that serves as the binding site for RNA polymerase, the enzyme that transcribes DNA into RNA. In the context of the video, promoters are essential components of operons, where they initiate the transcription process, which is a key step in gene expression.

💡Operator

The operator is a specific DNA sequence that acts as a control point for the initiation of transcription. It is part of the operon and can bind repressor proteins to regulate the activity of the operon. The video explains how the operator, along with the promoter, controls whether transcription occurs or not.

💡Repressor

A repressor is a protein that binds to the operator site and prevents RNA polymerase from binding to the promoter, thus inhibiting transcription. The video discusses how repressors play a critical role in the regulation of gene expression by blocking the transcription process when certain conditions are met, such as the presence of specific molecules.

💡Inducer

An inducer is a molecule that can bind to a repressor protein and change its shape, preventing it from binding to the operator and thus allowing transcription to proceed. The video gives the example of the lactose operon, where the inducer allolactose binds to the repressor, enabling the transcription of genes involved in lactose metabolism.

💡Catabolite Activator Protein (CAP)

CAP is a protein that binds to specific DNA sequences and activates transcription when glucose levels are low. It is mentioned in the video as a sensor for glucose levels, which, in conjunction with other regulatory elements, controls the expression of genes involved in the metabolism of alternative carbon sources like lactose.

Highlights

Prokaryotic genetic material is concentrated in a specific location called the nucleoid.

Prokaryotic genetic material also exists in the form of a single circular double-stranded DNA molecule attached to the plasma membrane.

Bacterial chromosomes do not contain histone proteins, distinguishing them from eukaryotic chromosomes.

E. coli DNA consists of a single circular molecule containing 4.288 genes organized into 2,584 operons.

Many bacteria also carry extrachromosomal genetic elements known as plasmids.

Gene expression in prokaryotes can be regulated through feedback inhibition and gene expression control.

Feedback inhibition stops gene expression when the product of a gene is in sufficient quantity.

Gene expression is regulated at the transcription level in prokaryotes.

The operon model is a key system for gene regulation in prokaryotes, consisting of genes located close together on the chromosome.

An operon includes a promoter, operator, repressor protein, and structural genes.

The promoter is where RNA polymerase binds, and the operator controls the activation of transcription.

The repressor protein can bind to the operator, blocking RNA polymerase and halting transcription.

The inducer molecule can bind to the repressor, causing it to detach from the operator and allowing transcription to proceed.

The lactose (lac) operon is an example of how gene regulation works in prokaryotes, being induced by the presence of lactose.

The trp operon is an example of negative feedback regulation, where excess tryptophan inhibits its own production.

Regulation can be negative, where gene expression is usually active but can be inhibited, or positive, where gene expression is usually inactive but can be activated.

The cAMP receptor protein (CRP) plays a role in the positive regulation of gene expression in prokaryotes.

Gene regulation in prokaryotes is crucial for adapting to environmental changes and nutrient availability.

Transcripts

[Musik]

asalamualaikum warahmatullahi

wabarakatuh Selamat pagi salam sejahtera

buat kita semua hari ini kita akan

membahas mengenai regulasi ekspresi gen

pada

prokariota materi genetik pada

prokariota atau prokariotik

adalah terkonsentrasi Biasanya

terkonsentrasi pada suatu tempat

tertentu eh pada bagian dari sitoplasma

yang disebut sebagai

nukleoid Selain itu materi genetik pada

prokariota juga berada pada

kromosom jadi kromosom Bakteri adalah

molekul DNA tunggal melingkar jadi

sirkuler berentai ganda yang sebagian

besar melekat pada P plasma membran pada

satu

titik kromosom pada bakteri ini tidak

mengandung protein hisiston ini nanti

yang akan membedakan dengan

eukariotik

eh sebagai contoh DNA

eserisakoli terdiri dari suatu molekul

sirkuler dengan panjang 4,6 juta

pasangan basa yang mengandung

4.288 protein sebagai yang dikode suatu

gen yang diorganisasikan menjadi

2.584 operon tujuh operon diantaranya

ada di merupakan RNA ribosom atau R RNA

dan 86 RNA transfer atau trna jadi

gen-gen yang mengkode RNA ribosom dan

gen-gen yang mengkode eh RNA

transfer selain pada DNA kromosom ee

banyak bakteri juga membawa unsur

genetik

ekstrakromosomal yang berbentuk molekul

DNA yang kecil juga sirkuler dan

tertutup yang disebut sebagai

plasmid nah tentang ekspresi gen pada

prokariota ya ekspresi gen untuk menjadi

protein itu dapat melalui dua mekanisme

yang pertama adalah feedback inhibition

dan yang kedua adalah melalui Gene

expression pada feedback inhibition saat

produk dari suatu genin sudah mencukupi

maka sistem ekspresi Akan Berhenti

bekerja sehingga selama produk tersebut

masih belum mencukupi maka ekspresi Gin

akan terus berlangsung umumnya ini

digunakan atau berlangsung untuk

bahan-bahan atau produk yang memang

selalu dibutuhkan oleh sel Nah

selanjutnya saat produk sudah cukup maka

maka produk tersebut akan menghentikan

proses ekspresi jadi dengan adanya

produk yang berlebih maka produk itu

menghentikan ekspresi kontrol yang kedua

adalah dengan melakukan regulasi

ekspresi gen di mana Gen hanya akan

diekspresikan saat dibutuhkan saja jadi

regulasi yang dilakukan di sini umumnya

dilakukan melalui proses

transkripsi untuk kontrol ekspresi gen

pada prokariota itu ada sistem yang kita

sebut sebagai

operon operon adalah gen-gen yang

mempunyai yang terkait yang terletak

berdekatan pada kromosom di dalam

kromosom gen-gen tersebut diaktifkan

atau dinonaktifkan secara bersama-sama

dan mempunyai promoter yang sama itu

yang disebut sebagai eh operon terlihat

dari gambar di

sini nah ekspresi gen pada prokariot

tadi Eh dikontrol oleh operon tadi itu

unsur-unsur dari operon atau komponen

dari operon itu terdiri dari ada

promoter operator ada protein represor

ada gen struktural nah promotor adalah

bagian DNA tempat RNA polimerase

berikatan sedangkan operator itu

mengontrol aktivasi transkripsi yang

merupakan saklar hidup atau matinya

suatu sistem Dalam hal ini eh terjadi

transkripsi atau tidak terjadi

transkripsi melalui

pengaturan ikatan antara promotor ee

Maaf eh dia berada di antara promotor

dan Gen untuk yang menghasilkan protein

atau gen

struktural yang kedua maaf yang ketiga

yaitu protein represor protein represor

itu akan berikatan dengan operator untuk

memblokir RNA polimerase sehingga RNA

polimerase tidak bisa berikatan dengan

operator dan menyebabkan transkripsi

berhenti

jadi mematikan atau menghentikan overon

eh di sini ada corpresor corpresor ini

adalah menjaga agar protein represor

berada pada operator nah ini yang

terjadi pada operon

triptovan selain kpresor yang bekerja

berkaitan dengan represor itu adalah

injuser injuser itu berfungsi untuk

menarik atau melepaskan represor dari

operator sehingga menyebabkan operator

menjadi aktif karena bisa berikatan

dengan RNA polimerase Nah contoh untuk

ini adalah pada operon laktosa

Eh ada gen regulator jadi gen regulator

ini sebenarnya berkaitan dengan represor

tadi jadi yang menghasilkan protein

represor ataupun aktivator atau

injuser sedangkan gen struktural itu

adalah gen yang mengkode protein jadi

itu adalah komponen keseluruhan dari

operon

ini sebagai contoh dari operon pada

prokaryiota yaitu lak operon atau operon

lak jadi operon l ini operon l dari

eekoliisiaakoli Ini mengandung gen yang

terlibat dalam metabolisme laktosa

operon ini diekspresikan hanya jika ada

laktosa dan tidak ada glukosa jadi hanya

ada laktosa glukosa tidak ada ada dua

regulator yang menghidupkan atau

mematikan operon sebagai respon terhadap

kadar laktosa dan glukosa yaitu represor

lak dan protein aktivator katabolit atau

katabolaid aktivator protein yang Biasa

disingkat dengan cap atau cap nah

represor lak bertindak sebagai sensor

laktosa biasanya menghambat transkripsi

operon tetapi Berhenti bekerja sebagai

represor ketika terdapat laktosa

represor lak ini mendeteksi laktosa

secara tidak langsung melalui isomernya

yaitu

alolaktosa nah protein cap tadi

bertindak sebagai sensor glukosa jadi

berbeda dengan yang represor lak tadi ya

jadi cap mengaktifkan transkripsi operon

hanya pada saat kadar glukosa

rendah Jadi cap mendeteksi keberadaan

glukosa secara tidak langsung melalui

molekul sinyal lapar atau Hunger sinyal

cimp atau cylic adenosin monofosfat

suatu second messenger yang diproduksi

dalam sel sebagai respon terhadap hormon

ataupun nutrisi ini adalah tentang lak

operon jadi lak operon ini ini

ringkasannya lak operon ini adalah

indusibel jadi bisa diinduksi hanya

hidup bila laktosa tidak ada dan EE

tidak diperlukan di dalam sel nah

terdapat dua kemungkinan kondisi yang

mempengaruhi kerja operon lak yang

pertama bila tidak ada laktosa maka

represor akan aktif dan akan berikatan

dengan operator sehingga menghalangi RNA

polimerase berikatan dengan operator

ketika RNA polimerase tidak bisa

berikatan dengan operator maka

transkripsi tidak terjadi jadi operon

tidak bekerja transkripsi tidak terjadi

yang kedua unuk gambar yang B bila

laktose ada maka alolaktose suatu

injuser akan berikatan dengan represor

menyebabkan represor menjadi tidak aktif

sehingga tidak bisa berikatan dengan

operator dan tidak menghalangi pelekatan

RNA polimerase pada operator tersebut

sehingga terjadi

transkripsi

eh selanjutnya contoh yang lain adalah

operon trp

operon trp ini berisi gen-gen yang

mengkode enzim yang mensintesis asam

amino

triptopan gen regulator pada trp operon

Ini menghasilkan protein represor nah

represor diaktifkan sama dengan yang

tadi pada laktosa juga lakoperon

represor diaktifkan dengan mengikat

triptofan dan memblokir transkripsi

dengan berikatan dengan operator nah

opon trp bekerja dengan mekanisme

feedback negatif jadi berbeda dengan

yang eh operon lak tadi mematikan operon

jika terdapat banyak triptofan atau

feedback mekanisme yang sudah saya

singgung di awal

tadi Nah ini eh gambar dari bagaimana

operon triptofan

bekerja ketika triptofan tidak ada maka

represor menjadi tidak aktif jadi tidak

aktif artinya dia tidak berikatan dengan

operator menyebabkan operon menjadi on

atau bekerja menjadi aktif terjadi

transkripsi sementara saat triptofan Eh

ada maka

represor akan berikatan dengan triptofan

tersebut dan kemudian menyebabkan bisa

berikatan dengan

operator sehingga operon kemudian karena

ketika operator berikatan dengan or maka

RNA polimerase menjadi

eh tidak bisa berikatan dengan operator

dan menyebabkan transkripsi tidak

terjadi sehingga poin-poin penting dari

eh apa yang saya sampaikan hari ini

adalah bahwa

eh ada dua regulasi sebenarnya di dalam

regulasi ekspresi Gin pada prokariotik

yaitu yang pertama regulasi negatif yang

kedua adalah regulasi positif

regulasi negatif artinya adalah regulasi

yang dapat

ditekan biasanya dalam keadaan normal

dia aktif tetapi dapat dihambat Kalau

misalnya tidak diperlukan contohnya

adalah operon trp tadi di mana terjadi

penghambatan alosterik di mana triptofan

akan mencegah produksi dari dia sendiri

ketika jumlahnya sudah berlebih ini umum

terjadi pada reaksi

anabolik yang bahwa regulasi negatif ini

dapat

diinduksi jadi yang biasanya tidak aktif

Jadi biasanya operon tidak aktif tapi

dapat diaktifkan dengan menggunakan

suatu indjuser atau molekul kecil

tertentu contohnya adalah alolaktosa

dalam operonlak yang menonaktifkan

represor dan memungkinkan

transkripsi ini umum terjadi untuk

reaksi

katabolik kedua adalah regulasi

positif contohnya bila eserisia itu

lebih suka menggunakan glukosa sebagai

sumber

energi eserisiakoli hanya akan

menggunakan laktosa ketika persediaan

glukosa

terbatas bila glukosa jumlahnya sedikit

maka camp tadi yang sudah saya sampaikan

sebelumnya akan berikatan dengan protein

pengatur tadi katabolik aktivator

protein atau cap dan merangsang

terjadinya transkripsi Gin sehingga

disebut regulasi positif kombinasi camp

dan cap memungkinkkan RNA polimerase

mengikat promotor dengan lebih efisien

jadi itu hal-hal yang penting dari eh

regulasi ekspresi gen pada prokariot

Terima kasih wasalamualaikum

warahmatullahi

[Musik]

wabarakatuh

[Musik]

than you