Genetic Expression

Question 1

Define/Explain the steps of Central Dogma

Answer 1

Flow of information in the cell

DNA->transcription->mRNA->translation->protein

Question 2

What is the promotor

Answer 2

DNA sequence that directs/regulates transciption
site of RNA polymerase
-35 to -10

Question 3

What direction do you read the template strand

Answer 3

3’ -> 5’

Question 4

How many nucleotides form a protein

Answer 4

three

Question 5

DNA is read (transcription occurs) in the _’ to _’ end

Answer 5

3’ to 5’ (making RNA 5’ to 3’)

Question 6

What direction does the template run away from the promotor

Answer 6

3’ to 5’

Question 7

Transcription changes _____ into ______

Answer 7

DNA into RNA

Question 8

What is RNA polymerase

Answer 8

Enzyme of transcription

• binds double stranded DNA at promotor
• unwinds double helix, create transcription bubble
• initiate transcription at +1
• aligns first two ribonucleotides (5’ end of new mRNA)

Question 9

How is the template strand chosen

Answer 9

Based on direction of promotor

Question 10

What happens at termination of transcription

Answer 10

RNA sequence that signal the end (terminators), RNA polymerase dissociates (falls off)

Question 11

Where does transcription happen, where does translation happen (in eukaryotes)

Answer 11

transcription: in nucleus
translation: in cytoplasm

Question 12

Post-transcriptional processing only happens in _________ because ________________________.

Answer 12

1. eukaryotes
2. transcription occurs in the nucleus, translation occurs in cytoplasm (time btw end of transcription and start of translation)

Question 13

What modifications occur in post-transcriptional processing? Why?

Answer 13

1. Addition of methyl guanosine cap at 5’ end: “hides” the 5’ end from exonuclease digestion
2. Addition of 100-200 adenosines to 3’ end (poly-A tail): prevent and delay exonuclease digestion, aids in translation initiation

Question 14

What is RNA splicing

Answer 14

removal of introns

Question 15

What are introns and exons

Answer 15

Introns (remove): non amino acid coding regions (intervening sequences) found on genes DNA but not mature RNA
Exons (leave): amino acid coding regions

Question 16

What is the spliceosome

Answer 16

Enzyme, complex of snRNPs, recognize sequence at intron/exon boundaries

Question 17

Steps of RNA splicing

Answer 17

1) SnRNPs bind intron/exon boundaries and loop out the intron
2) intron cut out by cutting at 5’ end of intron
3) excised intron in lariat shape (created by 5’-2’ linkage of RNA)
4) exons ligated together

Question 18

Why splice?

Answer 18

remove interrupting sequences, alternative splicing (mix and match of exons makes similar but not identical proteins from same gene. Ex. neuron vs muscular protein)

Question 19

Translation changes _____ into ______.

Answer 19

RNA into protein

Question 20

What signals start and stop of translation

Answer 20

start and stop codons

Question 21

mRNA vs tRNA

Answer 21

mRNA: codon
tRNA: anticodon (antiparallel and complementary to mRNA)

Question 22

Function of tRNA

Answer 22

carry appropriate amino acid to ribosome

Question 23

Function of Aminoacyl tRNA synthetases

Answer 23

“the translator”

pairs correct amino acid based on anticodon sequence, covalently links amino acid to tRNA in sequence dependent manner

Question 24

proteins are synthesized in what direction

Answer 24

N->C by reading mRNA 5’->3’

Question 25

Large vs small ribosomal subunits in prokaryote vs eukaryotes

Answer 25

Prokaryotes: 70s=30s(small)+50s(large) Eukaryotes: 80s=40s(small)+60s(large)

Question 26

The large ribosomal subunit contains _____ and its function is ______. The small ribosomal subunit contains _______ and is involved in _________________.

Answer 26

rRNA, catalytic, rRNA, recognition of mRNA

Question 27

The three sites of the large subunit

Answer 27

A:approach P:polymerization E:exit

Question 28

What is the ribosomal binding site

Answer 28

small ribosomal subunit in prokaryotes, sequence in mRNA that is recognized by base pairing with rRNA

Question 29

What are the three steps in translation (in prokaryotes)

Answer 29

Initiation, elongation, termination

Question 30

Briefly explain initiation phase in translation

Answer 30

ribosomal binding site positions the small subunit such that AUG sits in P-site, the large subunit then associates such that F-met tRNA sits in P-site "harmburger"

Question 31

Briefly explain elongation phase

Answer 31

BIND-BOND-SHIFT 1) Bind: tRNA a.a. approaches the A site and binds to mRNA (codon-anticodon) 2) Bond: peptide bond forms btw first and second tRNA and the growing a.a. chain moves to tRNA in A-site 3) Shift: 5' ribosome shifts down mRNA (towards 3') in a one codon step. tRNA in E-site dissociates

Question 32

Briefly explain Termination phase

Answer 32

Stop codons (UAA, UAG, UGA) stalls ribosome unless a release factor enters. Ribosome components dismantle and are recycled. Amino acid chain dissociates from tRNA in P-site.

Question 33

When do transcription and translation occur together

Answer 33

In prokaryotes! Ribosomes read mRNA as its being transcribed

Question 34

What direction do ribosomes move in

Answer 34

towards 3' end

Question 35

How many RNA polymerase can be active on one gene

Answer 35

Multiple! You can make many copies of mRNA from one copy of DNA

Question 36

What is a silent mutation?

Answer 36

Base pair substitution, but it works out and leads to the same amino acid (different codons can code the same protein)

Question 37

What is a missense mutation?

Answer 37

Base pair substitution that leads to the coding of a different amino acid

Question 38

What is a nonsense mutation?

Answer 38

Base pair substitution leads to coding pre mature stop codon.

Question 39

What is a frameshift mutation?

Answer 39

1. Base addition (or insertion) leads to premature stop | 2. Base deletion results in every amino acid after being affected

Question 40

When does a mutation not affect the reading frame

Answer 40

Deletion of multiples of three

Question 41

What causes sickle cell anemia

Answer 41

Single base pair substitution (MISSENSE), misshapes red blood cells so they do not carry oxygen well

Question 42

Explain how mutations can be spontaneous or induced

Answer 42

Spontaneous: errors in DNA replication (1x10^10 copied during replication result in mutation) Induced: x-rays, gamma-rays, oxidizing agents, base analogs Mutagens also cause cancer (carcinogens)