Chapter 17 - Gene Expression

Question 1

is RNA usually double or single stranded

Answer 1

single

Question 2

what is transcription?

Answer 2

the synthesis of RNA using information from DNA

Question 3

what is mRNA?

Answer 3

for a protein coding gene, the resulting complementary RNA strand is a transcript of the gene’s protein building instructions and is called mRNA because it carries a genetic message form DNA to ribosomes

Question 4

what is translation?

Answer 4

the synthesis of a polypeptide using information in the mRNA

RNA is translated into amino acid sequence of a polypeptide

Question 5

what is coupling? where does it occur?

Answer 5

bacteria don’t have nuclei so their DNA isn’t separated by nuclear membranes from ribosomes –> coupling means that ribosomes can attach to the 5’ end of a mRNA molecule while it is being made by transcription from the DNA template

in eukaryotic cell, the nuclear envelope separates transcription and translation

Question 6

what is RNA?

Answer 6

a sequence of ribonucleotides complementary to a DNA template

Question 7

What are the stop codons?

Answer 7

UAA, UGA, UAG

Don’t encode amino acids

Question 8

What’s the start codon for translation

Answer 8

AUG

Also codes for Met

Question 9

Difference between RNA and DNA polymerase?

Answer 9

RNA polymerase doesn’t need a primer!

Question 10

What’s a promoter?

Answer 10

A DNA sequence where RNA polymerase attaches and initiates transcription

Question 11

What does RNA pol I do?

Answer 11

Synthesize rRNA

Question 12

What does RNA pol II do?

Answer 12

Synthesizes mRNA

Question 13

What does RNA pol III do?

Answer 13

Synthesizes tRNA

Question 14

Set up of transcription

Answer 14

Promoter contains within it the start point –> RNA pol II binds to promoter only after transcription factors are attached to the promoter

The entire complex of transcription factors and RNA pol II bound to the promoter is called the transcription initiation complex

Question 15

What unwinds the DNA and starts transcription?

Answer 15

RNA pol II

Question 16

What’s the TATA box?

Answer 16

A nucleotide sequence within the promoter that upstream from the start point - a transcription factor has to bind to it first before RNA pol II can bind to DNA

Question 17

Elongation during transcription

Answer 17

A single gene can be transcribed simultaneously by multiple polymerase molecules, like a convoy –> increases amount of mRNA transcribed so cell can encode protein in large amounts

Question 18

Prokaryote vs eukaryotes termination of transcription

Answer 18

Bacteria: DNA goes through transcribed terminator sequence, detaches, and requires no further modification

Eukaryotes: RNA pol II transcribed a sequence from the DNA called the polyadenylation sequence (AAUAAA) –> 10 nucleotides downstream, certain proteins cut the DNA free from the polymerase and free the pre-mRNA –> RNA pol II continues to transcribe but new 5’ end isn’t protected by a cap so it’s degraded

Question 19

What is a 5’ cap

Answer 19

A modified form of guanine that’s added after transcription of the first 20-40 nucleotides

Question 20

What is a poly A tail?

Answer 20

After polyadenylation signal is transcribed and pre-mRNA is set free, enzyme then adds 50-200 more adenine (A) nucleotides

Question 21

RNA splicing

Answer 21

RNA splicing removes large portions of RNA that are initially synthesized

The noncoding segments of nucleic acid in RNA that lie between coding regions are called introns

The other regions are called exons because they will eventually be EXpressed (translated into amino acids)

Question 22

What removes introns from pre-mRNA

Answer 22

Removal of introns is accomplished by a large complex of proteins and small RNA called a spliceosome

Question 23

What is alternative RNA splicing

Answer 23

A single gene can encode more than more kind of polypeptide depending on which segments are treated as exons during RNA processing!

Question 24

What are the two ends of a tRNA

Answer 24

The 3’ end protrudes and is the attachment site for an amino acid

The other end is the anticodon which is the nucleotide triplet that base pairs to a specific mRNA codon

Question 25

What correctly matches up tRNA with its appropriate amino acid

Answer 25

Aminoacyl-tRNA synthetases –> the active site of each synthetases fits only a specific combination of tRNA and amino acid but each synthetases can fit all the tRNA for the specific amino acid

Catalyzes covalent attachment of amino acid to tRNA in a process driven by hydrolysis of ATP

Question 26

What is wobble

Answer 26

There isn’t a tRNA for each mRNA because there is flexible base pairing –> tRNA anticodon UCU can pair with mRNA codon AGA or AGG which both for for arginine

Difference is usually in the third codon

Question 27

Where are the subunits of ribosomes made?

Answer 27

Nucleolus

Question 28

Eukaryotic vs bacterial ribosomes

Answer 28

Eukaryotic are larger and different in molecular composition which is significant because certain antibiotic drugs can inactivate bacterial ribosomes without affecting eukaryotic ribosomes

Question 29

rRNA in translation

Answer 29

It’s primarily responsible for both structure and function of the ribosome and acts as a catalyst of peptide bond formation

Question 30

What energy does translation use

Answer 30

GTP

Question 31

What are the different ends of the polypeptide chain?

Answer 31

The chain is synthesized in one direction from the initial Met at the amino end called the N-terminus towards the final amino acid at the carboxyl end called the C-terminus

Amino acids are added one by one at the C-terminus

Question 32

Free vs bound ribosomes

Answer 32

Free ribosomes are suspended in the cytosol and synthesize proteins that say in the cytosol

Bound ribosomes are attached to the ER or nuclear envelope and make proteins of the engine brand system as wrk a proteins to be secreted from the cell

Ribosomes can alternate between being free or bound

Question 33

What are missense mutations?

Answer 33

Substitutions that change one amino acid to another

Don’t always do damage because functions of the amino acids can be similar to each other

Question 34

What’s a nonsense mutation

Answer 34

A point mutation that changes the codon for an amino acid into a stop codon and causes translation to be terminated prematurely –> resulting polypeptide will be shorter than the polypeptide encoded by the normal genes which usually leads to nonfunctional proteins

Question 35

What’s a frameshift mutation?

Answer 35

Occurs whenever the number of nucleotides added or deleted aren’t multiples of three and the result is missense which usually ends in nonsense and premature termination

Insertion or deletion usually alter the reading frame so the triplet groups are messed up –> usually worse than substitutions