Lesson 20: Gene Expression: Transcription

Question 1

What is gene expression?

Answer 1

The process by which DNA directs the synthesis of proteins, or, in some cases, just RNA

Question 2

What is transcription?

Answer 2

DNA is transcribed into RNA

Transcription is the synthesis of RNA using a DNA template

Question 3

What is translation?

Answer 3

RNA is translated into protein

Translation is the synthesis of a polypeptide using the genetic information encoded in an mRNA molecule

Question 4

What is the problem with the cell?

Answer 4

The DNA (instructions to make proteins) and ribosomes (protein factories) are not in the same place

Question 5

What are the two steps that protein production occur in?

Answer 5

Transcription and translation

Question 6

What does the ‘U’ pair with during transcription?

Answer 6

An RNA ‘U’ pairs with a DNA ‘A’ during transcription

Question 7

How do messenger RNA (mRNA) get made?

Answer 7

For protein coding genes, DNA serves as a template to produce a single stranded stranded messenger RNA

Question 8

What is an mRNA?

Answer 8

Carries the genetic information to the ribosomes, where the information is translated into proteins

Question 9

What is different about bacteria with their transcription?

Answer 9

In bacteria, transcription and translation are not separated into separate compartments, and they can occur simultaneously

Question 10

What is transcription overview?

Answer 10

Occurs in the nucleus, creates messenger RNA from a DNA template for one gene, mRNA is then edited and transported outside of the nucleus for translation

Question 11

What are the stages of transcription?

Answer 11

Initiation, elongation, and termination

Question 12

What happen to the strands during transcription?

Answer 12

During transcription the two strands of DNA separate, and only one of the two strands is used as a template for the mRNA

Question 13

What are some things that occur with the template strand in transcription?

Answer 13

For any gene, the same strand always serves as the template strand
Different genes on the same chromosome can use opposite strands of DNA as the template strand

Question 14

How are the mRNA and non-template strand related?

Answer 14

mRNA is synthesized in the 5’ to 3’ direction, and it is antiparallel to the template strand. The non-template strand has the same nucleotide sequence as the mRNA

Question 15

What is the non-template strand also called?

Answer 15

The coding strand

Question 16

What is RNA polymerase?

Answer 16

Links rubonucleotides into a growing RNA chain during transcription

Question 17

What are facts about RNA polymerase?

Answer 17

Based on complementary binding to nucleotides on a DNA template strand (C:G, A:U). Does not need primer, unlike DNA polymerase. Works in a 5’ to 3’ direction. Unwinds the DNA and goes to expose the template strand

Question 18

What is a promoter in transcription?

Answer 18

RNA polymerase attaches and begins transcription at the promoter

Question 19

What is the transcription unit in transcription?

Answer 19

The stretch of DNA that is transcribed into RNA

Question 20

What is the direction of transcription?

Answer 20

The direction of transcription is called downstream, the opposite direction is upstream

Question 21

How does transcription start in bacteria?

Answer 21

In bacteria, RNA polymerase binds directly to a specific sequence in the promoter

Question 22

How do eukaryotes initiate transcription?

Answer 22

In eukaryotes, other proteins, called transcription factors, bind to the DNA first. RNA polymerase forms a complex with the transcription factors called the transcription initiation complex

Question 23

What is a TATA box in eukaryotes?

Answer 23

Many promoters contain a specific sequence, TATAAAA, called the TATA box, to which transcription factors bind in order to establish the transcription initiation complex

Question 24

What is the start point in transcription?

Answer 24

The site where transcription actually begins. The promoter consists of DNA sequences dozens of nucleotides upstream from the start point

Question 25

What happens during elongation of transcription?

Answer 25

RNA polymerase untwists the DNA, exposing about 10-20 nucleotides at a time. RNA nucleotides that are complementary to the DNA template are added to the 3’ end of the growing RNA molecule

Question 26

What happens during termination of transcription in bacteria?

Answer 26

In bacteria, the terminator sequence in the DNA is transcribed into RNA, and the newly formed RNA forms a structure that causes the polymerase to fall off the DNA. The mRNA in bacteria doesn’t need to be processed and translation can begin

Question 27

What happens in termination of transcription in eukaryotes?

Answer 27

In eukaryotes, the RNA polymerase passes through a specific sequence of DNA that creates a polyadenylation signal (AAUAAA) in the pre-mRNA molecule

10-35 nucleotides downstream of the polyadenylation signal proteins that associate with the newly formed pre-mRNA cut it free from the RNA polymerase

Question 28

What is pre-mRNA?

Answer 28

Newly made mRNA

Question 29

What needs to happen to pre-mRNA before it leaves the nucleus in eukaryotes?

Answer 29

It must be modified as a mature mRNA. It undergoes extensive processing that alters both ends of the RNA and cuts sequences out of the middle

Question 30

What is primary transcript in RNA processing in eukaryotes?

Answer 30

The initial RNA transcript from any gene before it is processed

Question 31

What is the 5’ cap in RNA processing for eukaryotes?

Answer 31

The 5’ end of the pre-mRNA receives a 5’ cap, which is a modified guanine nucleotide

Question 32

What is a poly-A tail in RNA processing for eukaryotes?

Answer 32

A special enzyme adds 50-250 adenine nucleotides to the 3’ end. The long stretch of A’s is called the poly-A tail

Question 33

What do the 5’ cap and poly-A tail do in RNA processing for eukaryotes?

Answer 33

Protect the mRNA from degradation, are used to export the mRNA from the nucleus, and helps to attach ribosomes to the 5’ end of the RNA

Question 34

What are untranslated regions (UTRs) in RNA processing for eukaryotes?

Answer 34

Not all RNA nucleotides will be translated into amino acids. The regions of RNA that are not translated are called UTRs

Question 35

What do most eukaryotic genes have?

Answer 35

Long stretched of nucleotides that are not translated into protein

Question 36

What are introns in RNA splicing?

Answer 36

The non coding regions of nucleotides that lie between coding regions are called intervening sequences or introns

Question 37

What are exons in RNA splicing?

Answer 37

The regions of nucleotides that are expressed (usually translated into protein)

Question 38

What is the process of splicing?

Answer 38

Introns are cut out of the pre-mRNA (primary transcript) in a process called splicing

Question 39

What are spliceosomes in RNA splicing?

Answer 39

A large complex of proteins/RNA that splices mRNA by interacting with the ends of an RNA intron, releasing the intron, and joining the two adjacent exons

Question 40

What is alternative RNA splicing?

Answer 40

Creates different mRNA molecules from the same primary transcript, depending on which RNA segments are treated as exons and which as introns

Question 41

What are domains and what do they do in alternative RNA splicing?

Answer 41

Exons can correspond to functional domains in a protein

Discrete structural and functional regions. Different exons can code for different domains. Alternative splicing can produce proteins with different functions by adding or removing specific domains