Translation

Question 1

translation

Answer 1

• first step in protein synthesis

- the code contained in a mRNA is translated into a particular series of amino acids to form a polypeptide

Question 2

codon

Answer 2

-a nucleotide triplet of mRNA

Question 3

how many possible combinations of codons are there?

Answer 3

4 different nucleotides
3 nucleotides in each codon
64 total possibilities

Question 4

what direction are the nucleotides read and the proteins synthesized

Answer 4

• nucleotides are read from 5’ to 3’

- proteins are synthesized from N-terminus to C-terminus

Question 5

Start codon

Answer 5

• start codon is always AUG
• AUG encodes for methionine
• ALL START CODONS ARE AUG BUT NOT ALL AUG ARE START CODONS

Question 6

methionine

Answer 6

• AUG is the only codon that encodes for methionine

- other amino acids have multiple codons

Question 7

Stop codons

Answer 7

• DO NOT CODE FOR AN AMINO ACID
• UGA, UAA, UAG
• the first stop codon is THE stop codon

Question 8

What are the characteristics of the genetic code?

Answer 8

• universal
• specific
• redundant
• nonoverlapping
• commaless

Question 9

Universal

Answer 9

-genetic code defines the same amino acids in almost all organisms

Question 10

specific

Answer 10

each codon is specific to a certain amino acid

Question 11

redundant

Answer 11

• each amino acid may have more than one codon

- each amino acid has between 1 and 6 codons

Question 12

nonoverlapping and commaless

Answer 12

-a continuous series of 3 bases, no overlap and no bases are skipped o repeated

Question 13

single nucleotide changes

Answer 13

• point mutations
• silent mutation
• missense mutation
• nonsense mutation

Question 14

silent mutation

Answer 14

• if the DNA sequence is mutated, so that the codon is changed, but still encodes for the same amino acid
• EX UCA and UCU both encode for serine

Question 15

missense mutation

Answer 15

• if the point mutation results in a codon that defines a different amino acid
• UCA to UCU goes serine to proline

Question 16

conservative mutation

Answer 16

a missense mutation that results in an amino acid with similar properties
-non-polar to non-polar amino acid

Question 17

nonsense mutation

Answer 17

• change results in a change from an amino acid to a STOP codon
• the earlier in the sequence this occurs, the worse

Question 18

Frameshift

Answer 18

• if the insertion/deletion is NOT a multiple of 3.
• usually results in a premature STOP codon and truncated protein
• generally a pretty severe mutation

Question 19

What if the insertion/deletion is in a multiple of 3?

Answer 19

-results in the insertion/deletion of an amino acid or amino acids

Question 20

splice site mutation

Answer 20

-changes in nucleotides involved in splicing RNA

Question 21

possible results of splice site mutations

Answer 21

• deletion of nucleotides from an exon
• leaving nucleotides from an intron in the final mRNA
• complete deletion of an exon from the final mRNA
• can be single nucleotide mutations

Question 22

trinucleotide repeat expansion

Answer 22

• regions in a gene where a sequence of bases is repeated many times
• the repeat is amplified significantly

Question 23

where can trinucleotide repeat expansion happen?

Answer 23

• in the coding region

- in the 5’ or 3’ UTR

Question 24

result of trinucleotide repeat expansion in the coding region

Answer 24

• a faulty protein

- protein aggregation

Question 25

result of trinucleotide repeat expansion in the 5' or 3' UTR

Answer 25

- decreased production of the protein due to the effect of the UTRs on translation - disrupts the protein expression

Question 26

components required for translation

Answer 26

- amino acids - tRNA - mRNA - ribosomes

Question 27

what if the amino acid encoded on the mRNA is not present?

Answer 27

-translation will stop at the codon specifying that amino acid

Question 28

CCA-3' terminus

Answer 28

- amino acid attachment site on tRNA | - if an amino acid is attached, the tRNA is charged

Question 29

Anticodon

Answer 29

- specific 3 nucleotide sequence that base pairs with the mRNA - pair the codon, then flip it

Question 30

aminoacyl-tRNA synthetases

Answer 30

- enzymes that attach amino acids to the corresponding tRNA | - each of these enzymes recognizes the amino acids and ALL of the tRNAs that correspond to that amino acid

Question 31

How many different aminoacyl-tRNA synthetases are in humans?

Answer 31

20!

Question 32

tRNA charging

Answer 32

- two step reaction 1. amino acid is covalently linked to the hydroxyl group on the 3' terminus of the tRNA via its carboxyl group 2. pyrophosphate generated is then cleaved to give energy

Question 33

is there energy involved in attaching the amino acid?

Answer 33

-yea buddy

Question 34

subunits of ribosomes

Answer 34

-exist separately until protein synthesis is about to begin

Question 35

A site

Answer 35

-site on ribosome that binds incoming aminoacyl-tRNA

Question 36

P site

Answer 36

-site on ribosome that binds peptidyl-tRNA, which carries a chain of amino acids that have already been synthesized

Question 37

E site

Answer 37

- exit site on ribosome - contains empty tRNA as it is about to exit the ribosome - ONLY FOR PROKARYOTIC RIBOSOMES

Question 38

Do eukaryotic rbosomes have an E site?

Answer 38

-nope

Question 39

Where are eukaryotic ribosomes located?

Answer 39

-free in the cytosol OR -bound to the ER

Question 40

rough ER

Answer 40

-ER bound with ribosomes

Question 41

secretory proteins

Answer 41

-proteins translated on the ER are destined for post-translational modifications and or subcellular compartmentalization

Question 42

Where are prokaryotic ribosomes located?

Answer 42

-only free in the cytosol

Question 43

Energy requirements for translation

Answer 43

- Charging the tRNA: 2 ATP - Binding the aminoacyl-tRNA to the A site: one GTP - Translocation step: one GTP

Question 44

total energy needed for translation

Answer 44

-4 high energy bonds are required for each amino acid that is added

Question 45

Wobble hypothesis

Answer 45

- tRNAs can recognize more than one codon for a specific amino acid - 3rd nucleotide of a codon and the 1st nuceotide of the anticodon can SOMETIMES pair non-specifically

Question 46

polycistronic

Answer 46

- multiple coding regionson the same genes | - multiple genes on one mRNA

Question 47

polyribosomal

Answer 47

-multiple ribosomes can bind and work on a single mRNA molecule

Question 48

what kind of organisms are polycistronic?

Answer 48

prokaryotes only

Question 49

what kind of organisms can be polyribosomal?

Answer 49

-prokaryotes and eukaryotes can be this

Question 50

initiation of translation in prokaryotes

Answer 50

- presence of a shine-dalgarno sequence - 16S rRNA contains a complimentary sequence to the shine-dalgarno - this allows for correct alignment of the small ribosomal subunit with the AUG start codon

Question 51

initiation of translation in eukaryotes

Answer 51

-16S rRNA recognizes the 5' cap structure(scanning event)

Question 52

prokaryotic initiator tRNA

Answer 52

-bound to a formylated methionine

Question 53

eukaryotic initiator tRNA

Answer 53

-bound to a methionine

Question 54

elongation

Answer 54

- the polypeptide chain is elongated by the addition of amino acids to the carboxyl end of the growing chain - forms peptide bonds

Question 55

translation outline

Answer 55

- aminoacyl-tRNA to the A site - move uncharged tRNA into the E site - move peptidyl-tRNA into the P site - opens A site for the next aminoacyl-tRNA

Question 56

termination

Answer 56

- stop codon enters the A site - no tRNA can come in, so it terminates - releases polypeptide from the E site into the cytosol

Question 57

default pathway for proteins

Answer 57

-outside of the cell

Question 58

secretory pathway

Answer 58

-go into an organelle or another part of the cell