DNA Chapter 7.4 Flashcards Preview

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Flashcards in DNA Chapter 7.4 Deck (30)
1

Transcription

Uses a DNA template to create RNA.
. Transcription produces an RNA copy of one gene

.the cells uses the information from RNA and not the DNA directly to make each protein.

2

Transcription vs DNA replication ( the 2 main differences

Complementary base pairings underlies transcription just as it does DNA replication. They resemble except for:
1. The product of transcription is RNA , not DNA
2. Transcription copies just one gene from DNA strand, rather than copying both strands of an entire chromosome.

3

In Transcriptiion, RNA nucleotides base binds with

exposed complementary bases on the template strand ( which is the strand in the DNA molecule that is actually copied to RNA

4

Template Strand

The strand in the Dna molecule that is actually copied to RNA

5

The 3 Steps of Transcription

1. Initiation
2. Elongation
3. Termination

6

Initiation

1.Enzymes unzip The DNA double helix, exposing the template strand.

2. RNA POLYMERASE ( the enzyme that builds an Rna chain) binds to the PROMOTER (A DNA sequence that signals the gene's start)

7

RNA POLYMERASE

the enzyme that builds an Rna chain

8

PROMOTER

A DNA sequence that signals the gene's start

9

Elongation

RNA polymerase moves along the DNA template strand in a 3' to 5' direction, adding nucleotides only to the 3'-end of the growing RNA molecule. ( the creating of the copy of the DNA template: the copy: mRNA )

10

Termination

1. A TERMINATOR sequence signals the end of the gene.

2. Upon reaching the terminator sequence, the RNA POLYMERASE enzyme separates from the DNA template and releases the newly synthesized RNA. ( mRNA)

3. The DNA molecule resumes its usual double helix shape

11

What happens to the RNA molecule as it is synthesized

It curls into a 3 dimensional shape dictated by complementary base pairing within the molecule

12

What does the final shape of RNA determines

whether the RNA functions as mRNA, rRNA, OR tRNA.

13

. What happens during each stage of transcription

The steps of transcription are initiation, elongation of the RNA molecule, and termination. During initiation, enzymes unzip the DNA and RNA polymerase binds. During elongation, RNA polymerase “reads” the DNA strand and adds complementary nucleotides to the growing RNA strand. During termination, synthesis of the RNA molecule ends and the DNA molecule reforms.

14

Where in the cell does transcription occur

Transcription occurs in the nucleus.

15

What is the role of RNA polymerase in transcription?

RNA polymerase uses the DNA template to bind additional RNA bases into the growing chain of RNA being transcribed.

16

What are the roles of the promoter and terminator sequences in transcription

The promoter signals the start of a gene, and the terminator signals the end of a gene. RNA polymerase recognizes the promoter and terminator, so it starts and stops transcription at the correct positions.

17

How is mRNA modified before it leaves the nucleus of a eukaryotic cell

Before it leaves the nucleus of a eukaryotic cell, mRNA is altered in the following ways:
- a cap is added to the 5’ end of the mRNA molecule;
- a poly A tail is added to the 3’ end;
- introns are removed and exons are spliced together.

18

The definition of gene has expanded how

Originally a gene was defined as any stretch of DNA that encodes one protein

. It has now been expanded to include any section of DNA that is transcribed ( protein or RNA as all types of RNA are transcribed not just mRNA)

19

Gene expression means

Production of either a functional RNA molecule or a protein.

20

Difference in prokaryotic and eukaryotic cells in transcription/ translation process

In prokaryotic cells ribosomes may begin translating mRNA to a protein before transcription is complete.

In eukaryotic cells the presence of the neuclear membrane prevents mRNA from being transcribed and translated simultaneously.

mRNA is usually altered before leaving the nucleus to be translated

21

What is a 5' cap and a poly A tail

What are their purpose

After transcription
a CAP ( a short sequence of Modified Nucleotides) is added to the 5' end of a mRna molecule.

Poly A tail: 100-200 adenines are added at the 3' end.

Together they enhance translation by helping ribosomes attach to mRNA molecule

22

What are their purpose of the a 5' cap and a poly A tail

Together they enhance translation by helping ribosomes attach to mRNA molecule

23

After transcription what two additional steps are done before the mature mRna exists the nucleus

1. 5' cap and Poly A tail is added
2. Introns are removed( leaving exons)

24

What does the length of the poly A tail determine

How long an m RNA last before being degraded

25

What is intron short for

Intragenic regions ( within gene)

26

Introns

Are portions of the mRNA that are not copied and are removed by catalytic RNAs and proteins before translation

27

The average Exon is how long

100-300 nucleotide long

28

Exons

The remaining portions once the introns are removed. They are spliced together to form a mature
mRNA

This is what leaves the nucleus to be translated

29

What are their purpose of the a 5' cap and a poly A tail

Together they enhance translation by helping ribosomes attach to mRNA molecule

30

prokaryotic vs. Eukaryotic : how quickly can ribosomes begin translating mRNA

In Bacteria and archaea, ribosomes may begin translating mRNA to a protein before transcription is even complete

Eukaryotes: 1.The presence of the nuclear membrane prevents one mRNA from being simultaneously transcribed
2. In eukaryote cells mRNA is altered before it leaves the nucleus to be translated