Ims: Dahlberg Block 1: Lecture 3 - 8/25

Front 1

What is the genetic code?

Back 1

aa sequence of mRNA

Front 2

What will happen if an amino acid is missing from a protein sequence during translation?

Back 2

Peptide synthesis will stop where aa should've been

Front 3

What vitamin assists in the manufacture of non-essential aa's? What happens if it is missing?

Back 3

B-6; all aa's become essential

Front 4

Which aa's are essential?

Back 4

Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
Methionine
Histidine
Arginine
Leucine
Lysine

Front 5

What is a codon? In what direction are they written?

Back 5

Three nucleotides that code for an aa.

5'-->3'

Front 6

What are the three stop codons? What is their purpose?

Back 6

UAG
UGA
UAA

Signal end of translation of a particular species of mRNA

Front 7

How are codons unambiguous?

Back 7

Each codon only codes for ONE amino acid

Front 8

What is the exception to the universality of the genetic code?

Back 8

Mitochondria

Front 9

How is the genetic code redundant/degenerate?

Back 9

an aa may be encoded by more than one codon

Front 10

How would you find the 5' end of an amino acid sequence if you are only given its chemical structure? The 3' end?

Back 10

5' end = amino terminus
3' end = carboxy terminus

Front 11

What is a silent mutation?

Back 11

Altered codon still encodes same aa

Front 12

What is a missense mutation?

Back 12

altered codon codes for a different aa

Front 13

What is a nonsense mutation?

Back 13

altered codon is a TERMINATION codon

Front 14

What is the genetic mechanism for the onset of Huntington's Disease?

Back 14

Tandem repeats in number of CAG codons (glutamine); results in protein that has add'l glutamines and makes protein unstable

Front 15

What is a frame-shift mutation?

Back 15

add/remove nucleotide and throws reading of codons off. usually results in premature stop codon.

Front 16

What is a splice site mutation?

Back 16

add/remove nucleotide in area where splicing occurs; alters exon/intron architecture

Front 17

How many tRNA's are there per aa? Codons? What does this say about tRNA's?

Back 17

At least one; tRNA's can read more than one codon

Front 18

What is the energy source of tRNA's?

Back 18

ATP

Front 19

What is the energy source of translation factors? What do these factors allow for?

Back 19

GTP; facilitators of start, stop and go

Front 20

Describe the anticodon nucleotide and codon structure of tRNA.

Back 20

Three base nucleotide that recoznies and base pair with specific sequence on mRNA

Anticodon is ANTI-PARALLEL and complimentary to the codon.

Front 21

What would the tRNA anticodon be for the following mRNA codon:

5'-AUG-3'

Back 21

3'-UAC-5'

Front 22

Describe the location and chemical composition of the amino acid attachment site of tRNA. What does bonding to this site require?

Back 22

Located on 3' end; Carboxyl group of aa forms ester linkage with 3'-OH of an adenosine on tRNA (HIGH ENERGY BOND) - REQUIRES ATP to form ester linkage

Front 23

What is an ester bond?

Back 23

When you bond to OH of of Carboxylic Acid

Front 24

What role to aminoacyl-tRNA synthetases play?

Back 24

mediate attachment of tRNA with its specific aa

Front 25

What is constant about the amino acid attachment site in all tRNA's?

Back 25

3' end is always CCA-OH.

Front 26

What does the Wobble Hypothesis state? What does this explain?

Back 26

First base of anticodon in tRNA (5' end) can engage in non-traditional base pairing with third base (3' end) of mRNA codon.

Explains how tRNA's can recognize more than one codon for a specific aa.

Front 27

How do the large and small subunit of the ribosome differ?

Back 27

Small ribosome binds mRNA (along with initiation factors AKA INITIATION COMPLEX)

Front 28

Describe the three sites in the ribosome.

Back 28

A site: site for incoming tRNA with bound aa

P site: site for tRNA with growing protein

E: site for tRNA after releasing aa and before it exits ribosome

Front 29

In what direction does the ribosome read mRNA?

Back 29

5'-->3'

Front 30

What occurs in the initiation phase of translation?

Back 30

1. Assembly: mRNA, aminoacyl tRNA specified by first codon (always METHIONINE: AUG = START CODON ALWAYS), initiaion factors (IF in prokaryotes, eIR in euks)

Now have fully fnal ribosome with first aa waiting to go!

2. Met tRNA enters P site; all others enter at A site

Front 31

Do all proteins have methionine at the N-terminus (start)?

Back 31

Yes, initially, but N-terminal methionine usually enzymatically removed.

Front 32

What do IF's do during initiation?

Back 32

aid in formation of 30S initiation complex

Front 33

When are initiation factors released?

Back 33

After GTP is cleaved and 50S subunit arrives to form 70S complex.

Front 34

What is streptomycin's mechanism of action?

Back 34

Binds 30S subunit and distorts structure; thus, interfering with initiation.

Front 35

Describe the process of elongation in translation.

Back 35

Ribosome moves 5'-->3' on mRNA
New tRNA's dock at A site
PEPTIDYLTRANSFERASE mediates formation of peptide bonds
AA's from tRNA in P site transferred to aa in A site
After peptide formation, ribosome advances 3 nucleotides in 3' direcn

Front 36

What role do elongation factors play in translation?

Back 36

Direct binding of appropriate tRNA to the codon in the empty A-site

REQUIRES GTP

Front 37

What is tetracycline's mechanism of action?

Back 37

interact with small ribosomal subunit to block access of aminoacyl-tRNA

Front 38

What is puromycin's mechanism of action?

Back 38

~structure to aminoacyl-tRNA and becomes incorporated into peptide chain, causing inhibition of further elongation

Front 39

Describe chloramphenicol's mechanism of action.

Back 39

Inhibits peptidyltransferase, high levels may also inhibit mitochondrial protein synthesis

Front 40

What is the role of peptidyltransferase?

Back 40

component of 50S ribo subunit, transfers aa from P-site onto aa at A site; catalyzes peptide formation

Front 41

Describe the mechanism of action for clindamycin and erythromycin.

Back 41

Bind irreversibly to 50S subunit of bacterial ribosome, inhibiting translocation.

Front 42

What is translocation?

Back 42

Movment of ribosome a distance of three nucleotides along MRNA in 5'-->3' direction.

Front 43

How does the diphtheria toxin work?

Back 43

Inactivates eukaryotic EF; thus preventing translocation.

Front 44

How does termination occur during translation?

Back 44

Termination codon recognized by a release factor, which releases peptide chain and dissolves ribosomal complex.

GTP!!

Front 45

What is the role of RNAi? Describe the process.

Back 45

Gene expression regulation;

micro-RNA's bind specific proteins to form complex with complementary sequences in specific mRNA's, blocking initiation of protein synthesis

si-RNA lead to cleavage of mRNA

Front 46

What are polyribosomes?

Back 46

numerous ribosomes translating a particular piece of RNA

Front 47

What does ubiquitination of a polypeptide chain do?

Back 47

adds small protein that signals for breakdown

Front 48

In what direction are amino acids synthesized?

Back 48

N-->C

Front 49

Are there more of fewer tRNA molecules than codons in human cells?

Back 49

Fewer--because of wobble hypothesis