Translation

Question 1

translation

Answer 1

process by which mRNA is decoded and a protein is produced

Question 2

which direction is mRNA translated?

Answer 2

5’ to 3’, into a protein from the amino (N)-terminus to the (C)-terminus

Question 3

what is the start codon for translation?

Answer 3

AUG (methionine)

Question 4

degenerate

Answer 4

the genetic code is referred to this since more than one codon can code for the same amino acid, however it is unambiguous (each codon only specifies for one a.a)

Question 5

how do mutations arise?

Answer 5

as a result of DNA damage or incorrect incorporation of bases

Question 6

frameshift mutation

Answer 6

mutation that shifts the “reading” frame of the genetic message by inserting or deleting a nucleotide

Question 7

point mutation

Answer 7

gene mutation in which a single base pair in DNA has been changed

Question 8

silent mutation

Answer 8

alters a base but does not change the amino acid

Question 9

missense mutation

Answer 9

a point mutation in which a codon that specifies an amino acid is mutated into a codon that specifies a different amino acid

Question 10

nonsense mutation

Answer 10

changes a normal codon into a stop codon

Question 11

insertion

Answer 11

a mutation involving the addition of one or more nucleotide pairs to a gene

Question 12

deletion

Answer 12

a lose of one or more nucleotide bases

Question 13

what are the steps of translation?

Answer 13

initiation, elongation, termination

Question 14

tRNA in translation

Answer 14

• each tRNA molecule carries one type of amino acid
• the reaction requires ATP and once the a.a. is attached the tRNA is charged
• the tRNA for the start codon differs from tRNA that codes mot methionine within the protein
• charged tRNAs donate their a.a. to the protein chain while the anticodon is attached to the mRNA
• the tRNA is then released; the charged tRNA that codes for the next a.a attaches

Question 15

initiation of translation

Answer 15

• involves formation of a complex b/w the methionyl-tRNA, initation factors, the mRNA and the small ribosomal subunit (40S)
• the large subunit (60S) binds to complete the ribosome which has 2 binding sites for tRNAs, the peptidyl (P) and aminoacyl (A) sites

Question 16

elongation

Answer 16

peptidyltransferase catalyzes the formation of the peptide bond

Question 17

peptidyltransferase

Answer 17

the ribosome makes the peptide bonds that stitch amino acids together

Question 18

termination

Answer 18

• elongation continues until a stop codon is reached
• no tRNAs that match these codons so release factors bind to the ribosome, allowing the last peptide bond to form before releasing the new polypeptide
• requires a lot of energy expenditure

Question 19

what are the stop codons?

Answer 19

UGA, UAG, UAA

Question 20

posttranslational modifications

Answer 20

after the protein emerges from the ribosomes chaperone proteins help it to fold correctly
- a # of different modifications can then be made to the new protein

Question 21

glycolysation

Answer 21

a common posttranslational modification, especially for secreted or integral membrane proteins; y-carboxylation occurs in some of the proteins involved in blood coagulation

Question 22

protein targeting

Answer 22

the sorting and transportation of proteins from the site of synthesis on ribosomes to compartments in the cell where they are needed
- once proteins are released, those destined for the cytosol remain but where they are but those w/ “signal sequences” are targeted to the organelle in which they function (nuclear localization signals are an example)

Question 23

polysomes

Answer 23

multiple ribosomes can attach to an mRNA, each producing the same proteins

Question 24

what happens to proteins that will be secreted into membranes or organelles?

Answer 24

they are translated into the ER due to a SRP that causes the ribosome to dock onto the ER to complete protein synthesis

Question 25

signal-recognition particle (SRP)

Answer 25

binds to the signal peptide and brings the signal peptide and its ribosome to the ER

Question 26

proteins synthesized into the ER

Answer 26

proteins translated into the lumen of the ER are carried in the vesicles to the Golgi complex

• those proteins not destined to stay in the Golgi or go back to the ER heave in vesicles from the other side of the Golgi
• these vesicles either become lysosomes or fuse with the cell membrane to release secreted membrane proteins or imbed membrane-spanning proteins in the cell’s outer lipid bilayer

Question 27

Huntington’s disease

Answer 27

a human genetic disease caused by a dominant allele; extra CAGs in the gene lead to neurodegenerative disorder and death