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Cell and Molecular Bio > Transcription-13 > Flashcards

Transcription-13 Flashcards

1
Q

DNA vs RNA

A 
DNA (deoxyribonucleic acid)
Sugar: Deoxyribose
N bases: A, C, G and T 
Complementary base pairing A-T 
Double stranded and longer in length 
Exists in 1 form 
More stable-less reactive due to C-H bond at 2nd Carbon position

RNA (Ribonucleic acid)
Sugar: ribose
N bases: A,C,G and U
Complementary base pairing A-U
Single stranded and shorter in length
Exist in several forms such as mRNA, rRNA and tRNA
Less stable-more reactivity due to C-OH bond at 2nd carbon position

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2
Q

Gene expression:

A

Every cell of the body (with a dew exceptions) contains a full set of chromosomes and identical genes

Only a fraction of these genes is turned on, however, and it is the subset that is “expressed” that confers unique properties to each cell type

[] Proper expression of a large number of genes is a critical component of normal growth and development and the maintenance of proper health

[] Disruptions or changes in gene expression are responsible for many diseases

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3
Q

What is gene regulation?

A

Gene regulation refers to the ability of cells to control their level of gene expression

Majority of genes are regulated so proteins produce at certain times and in specific amounts

Constitutive genes are unregulated and have essentially constant levels of expression

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4
Q

What are the benefits of gene regulation?

A
  1. Conserves energy- proteins produced only when needed

2. Ensures genes expressed in appropriate cell type and at the correct stage in development

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5
Q

Define Gene expression:

A

process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins

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6
Q

What is the purpose of Gene expression in the Central Dogma of Biology?

A

Serves as a blueprint to make RNA

DNA acts as a template for making RNA, which in turn acts as a template for the manufacture of proteins

During gene expression (protein synthesis), transcription copies DNA into RNA, and translation makes proteins from RNA

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7
Q

Where does transcription take place?

A

Nucleus

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8
Q

What is genomic DNA?

A

contains the master blueprint for all cell structures and activities

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9
Q

Where does Translation take place?

A

Ribosomes

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10
Q

What is mRNA?

A

Messenger RNA are the specific, short lived gene transcription

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11
Q

Translation:

A

From RNA nucleic acid language

3 nucleotides-genetic code) to protein amino acid language (20 amino acids

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12
Q

Gene expression: an Overview

Transcription and Translation

A

Transcription: the first step of gene expression. The sequence of nucleotides in DNA is copied to a sequence of nucleotides in mRNA (the transcript)

Translation: the second step, mRNA is translated into a sequence of amino acids

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13
Q

What is transcription?

A

process of making an RNA copy of a single gene

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14
Q

What is a gene?

A

specific regions of the DNA of a chromosome

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15
Q

How do cells know which gene to express?

A
  1. Ligand (first/primary messenger) aka signals to bind to specific receptors of the cells
  2. Trigger a series of signaling pathway (aka signal transduction) to activate the target proteins which serve as transcriptional factors
  3. Target proteins enter the nucleus, together with other regulatory proteins to form the transcriptional complex to activate the transcription of the genes of interest
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16
Q

What is the product of transcription?

A

RNA

17
Q

What is the enzyme for performing transcription?

What are the substrates used?

A

RNA polymerase

RNA synthesis uses NTPs (ATP,CTP,GTP,UTP) as substrates

18
Q

Overview of transcription strands:

A

DNA double helix has 2 strands
Only ONE of them is transcribed:

Transcribed strand: template strand or antisense strand

Non-transcribed strand: coding strand or sense strand

RNA is complementary to the template or antisense strand

The RNA has the same sequence as DNA coding or sense strand

19
Q

What are the 3 stages of Transcription?

A
  1. Initiation
  2. Elongation
  3. Termination
20
Q

What are transcription factors?

A

proteins that regulate the transcription of genes

21
Q

When does transcription begin?

A

Transcription begins when RNA polymerase (RNAP) binds to a promoter sequence near the beginning of a gene (directly or through helper proteins)

22
Q

What occurs during the initiation stage of Transcription?

A
  1. Begins with RNA polymerase binding to a promoter sequence near the beginning of a gene (directly or through helper proteins)
  2. After polymerase is bound to the promoter DNA, the two strands unwind and the enzyme starts transcribing the template strand
  3. The region of opened up DNA is called a transcription bubble
23
Q

What occurs during the initiation stage of Elongation?

A
  1. RNA polymerase moves along DNA template and adds nucleotides in the 5’-3’ direction
  2. RNA polymerase reads the template DNA strand and adds nucleotides to the 3’ end of a growing chain
  • new nucleotides are added at an estimated rate of about 42-54 nucleotides per second in bacteria
  • eukaryotes proceed at a much slower pace of approximately 22-25 nucleotides per second
  1. produces an RNA copy that is complementary to the template
  2. As RNA polymerase moves long, DNA double helix reforms
24
Q

What occurs in the termination stage of Transcription?

A

1- Transcription stops when RNA polymerase reaches DNA terminator

  1. RNA strand is released
25
Q

How to process mRNA in bacteria and eukaryotes?

A

In bacteria, RNA transcripts are ready to be translated right after transcription

In eukaryotes, mRNA is processed before leaving the nucleus
-the processing RNA refers to changing the new premature mRNA into a mature mRNA

26
Q

What are introns?

A

noncoding sections of a gene, they don’t code for a functional protein

27
Q

What are Exons?

A

portions of the gene that are expressed, result in a protein product

28
Q

How is splicing of the mRNA carried out?

A

The introns are removed, and the exons are joined to form a mature mRNA molecule

Is done by a complex called spliceosome, which is composed of both RNA and protein

29
Q

What is alternative splicing?

A

Method cells use to create many proteins from the same strand of DNA

It produced different mature mRNAs containing various combinations of exons from a single precursor mRNA

One single gene can result in different protein versions

30
Q

Post-transcriptional processing

A

Both ends of a mRNA are modified by the addition of chemical groups

  • add 5’ GTP cap
  • add poly-A-tail

Mature mRNA is transported through nuclear pores to the cytoplasm

31
Q

Post-transcriptional processing

Why is the 5’ cap added?

A

The 5’ cap is added to the first nucleotide in the transcript during transcription

  1. The cap is a modified guanine (G) nucleotide, and it protects the transcript from being broken down
  2. Assists in ribosome binding during translation
32
Q

Post-transcriptional processing

Why is the poly-A-tail added?

A

The processing of the 3’ end adds a poly-A tail to the RNA molecule

This process is called polyadenylation, adds a poly-A-tail that is between 100 and 250 residues long

  1. The poly-A tail makes the RNA molecule more stable and prevents its degradation
  2. Longer tail, mRNA lasts longer: produces more protein
33
Q

Summary of post-transcriptional processing

A
  1. primary transcript= pre mRNA
  2. mRNA splicing
  3. edit out introns
  4. Add 5’ GTP cap and 3’ poly A tail
  5. make a mature mRNA
34
Q

Difference between transcription in bacteria vs eukaryotes

A

Bacteria:

  • 1 RNA polymerase
  • Proteins involved in recognizing promoter (sigma; different versions of sigma bind to different promoters)
  • No RNA processing

Eukaryotes:

  • 3 RNA polymerases each produces a different class of RNA
  • Proteins involved in recognizing promoter (many basal transcription factors)
  • Several processing steps occur
    1. ) Enzyme catalyzed addition of 5’ cap on mRNAs
    2. ) Splicing (intron removal) by spliceosome to produce mRNA
    3. ) Enzyme-catalyzed addition of 3’ poly (A) tail on mRNAs
35
Q

What are constitutive genes? How are they different in gene regulation?

A

Constitutive genes are unregulated and have essentially constant levels of expression

Cell and Molecular Bio (13 decks)

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