Lecture 6

Question 1

The nucelotide sequence of an mRNA is translated into the amino acid sequence of a protein via the

Answer 1

Genetic code

Question 2

The genetic Code

Answer 2

The way that information is stored in the DNA and how it can be read to make a protein

UNIVERSAL code = all organisms use this genetic code (some organisms may use certain codons more frequently)

Redundant: Most amino acids (EXCEPT for 2) have more than one codon that codes for it

Methianine (Met): START codon

Coded by AUG

Question 3

Codon

Answer 3

Contains 3 bases

Dictates what amino acid will be added to chain in the mRNA

Question 4

Redundancy

Answer 4

Most codons code for more than 1 amino acid

Question 5

In principle, an mRNA molecule can be translated into 3 possible reading frames

Answer 5

Reading frame: ribosome reads 3 bases at a time

Frame shift if you add 1 or 2 bases

Question 6

tRNA molecules are molecular adaptors, linking amino acids to

Answer 6

Codons

Question 7

Anticodon

Answer 7

Complementary to the codon in the mRNA

Question 8

tRNA is TRANSCRIBED but never

Answer 8

Translated

Question 9

Amino acid is ALWAYS added to the

Answer 9

3’ end (there is a conserved set of sequences on this end: CCA)

Question 10

On the other end:

Answer 10

Anticodon loop (complementary to the codon)

Question 11

Each aminoacyl-tRNA synthetase makes multiple contacts with its tRNA molecule

Answer 11

One per amino acid in cell

These are specific for the AMINO ACID, not the codon

Responsible for adding on amino acid to CCA on 3’ end of tRNA; specific to each amino acid in the cell

Question 12

The genetic code is translated by

Answer 12

Aminoacyl-tRNA synthetases and tRNAs

This will connect the amino acid to the very last A residue of the CCA

ATP dependent

Amino acid and tRNA w/in aminoacyl-tRNA synthetase (specific to amino acid) -> releases ATP -> Linkage of amino acid to tRNA by high-energy ester bond -> anticodon in tRNA binds to its codon in mRNA -> Net result: Amino acid is selected by its codon in an mRNA

Question 13

The eukaryotic ribosome is a large complex of 4 rRNAs and more than 80

Answer 13

Small proteins

rRNA is NOT translated to protein

Sibosomes are a COMPLEX of proteins and RNA

Question 14

rRNA

Answer 14

SAME in prokaryotes and eukaryotes

Question 15

Each ribosome has a binding site for an mRNA and 3 binding sites for tRNAs

Answer 15

Ribosome itself is considered a ribozyme (catalytic piece of RNA)

Question 16

Ribosome is a

Answer 16

Ribozyme

Question 17

Ribosomal RNA catalyzes peptide bonds to

Answer 17

Form

Question 18

Fibozyme

Answer 18

Catalyst version of rRNA

Question 19

Translation takes place in a 4-step cycle, which is repeated over and over during the Synthesis of a protein

Answer 19

Elongation:

1) 3 amino acids on protein; many tRNAs will attempt to attach, only the one that is complementary will attach
2) Peptide bond is formed; energy comes from the breakage of high-energy ester bond
3) Trigger conformational change in large ribosomeal subunit, resulting in a shift
4) Shifts down by 3 bases; 4th tTNA is in P site; empty tRNA is released; A site is left open for the next one

Question 20

A site

Answer 20

Acceptor site

Question 21

Initiation of protein synthesis in eukaryotes requires translation initiation factors and a special initiator tRNA

Answer 21

5’ cap binding protein and poly-A proteins get exchanged for other proteins to be used in translation

Question 22

In eukaryotic cells

Answer 22

Methianine is ALWAYS the start codon

Question 23

Small subunit has initiator tRNA (complex)

Answer 23

These initiation factors recognize and interact with cap scan for start codon

Question 24

Load up at cap

Answer 24

This is waht it recognizes

Scan message to look for AUG (start)

Question 25

mRNA binding at AUG ->

Answer 25

Small ribosomal subunit, with bound iniator tRNA, moves alond mRNA searching for first AUG

Question 26

Initiation factors dissociate (basically only there to recognize processed messages that are ready to be translated

Answer 26

Large subunit will dissociate first

ALL tRNAs enter at the A site EXCEPT for initiator tRNA, must enter at P site instead

Translation initiation factors dissociate

Large ribosomal subuni binds

Initiator tRNA will NEVER be in the A site; ALWAYS starts in the P site

Question 27

Monocistronic message

Answer 27

Eukaryotes

Only have ONE gen on RNA

Question 28

Polycistronic message

Answer 28

Prokaryotes

MANY genes can be on one mRNA

Question 29

Translations halts at a stop codon

Termination

Answer 29

1) Ribosome arrive at stop codon; there are NO tRNA’s involved
2) Realease/termination factor binds to the A site -> triggers the relaeas of everything (peptide chain, message and ribosoem dissociate); there is NO tRNA that would recognize a stop codon

Sae in ALL cells

Question 30

Proteins are synthesized on polyrbosomes

Answer 30

Messages will be translated many (hundred of) times

Question 31

Proteins are degraded by the proteasome AFTER translation

Answer 31

Proteins are targeted to be degraded

Degrading proteins within cell is important to get rid of damaged and old proteins

Proteasome: Chamber that gets rid of poroteins enzyme ccomplx

ubquitin marks proteins for destruction; proteasome just looks for ubiquitin tag

Proteases chop up proteins

Degrading proteins within cell is important process; cell gets rid of old/deteriorating proteins

Question 32

Proteins marked by a polyubiquitin are degraded by the proteasome

Answer 32

Chain of proteins

Question 33

Many proteins requrie post-transcriptional modifications to become fully functional

Answer 33

Most proteins will need to be modified

-Glycolysis, methylation, phosphorylation