chapter 9

Question 1

What is the Central Dogma of molecular biology?

Answer 1

DNA → RNA → Protein

Question 2

What are proteins made of?

Answer 2

Proteins are polymers of amino acids.

Question 3

What is the primary structure of a protein?

Answer 3

The linear sequence of amino acids in a polypeptide chain.

Question 4

What are the two common secondary structures of proteins?

Answer 4

• α-helix
• β-pleated sheet

Question 5

What defines tertiary structure in proteins?

Answer 5

The folding or interaction between secondary structures.

Question 6

What is quaternary structure in proteins?

Answer 6

Proteins composed of multiple folded polypeptides joined by weak bonds.

Question 7

What is the significance of protein shape?

Answer 7

Shape is essential to a protein’s function.

Question 8

Name two types of protein shapes.

Answer 8

• Globular proteins
• Fibrous proteins

Question 9

What is the role of transfer RNA (tRNA)?

Answer 9

tRNA translates codons into corresponding amino acids in a polypeptide.

Question 10

What does the Wobble Hypothesis propose?

Answer 10

tRNA can recognize two codons due to flexible base pairing.

Question 11

What is the genetic code described as?

Answer 11

Nonoverlapping and degenerate.

Question 12

How many nucleotides are in a codon?

Answer 12

Three nucleotides.

Question 13

What is a stop codon?

Answer 13

Codons that specify the end of translation.

Question 14

What experiment helped crack the genetic code?

Answer 14

Making synthetic mRNA using polynucleotide phosphorylase.

Question 15

What is the role of ribosomal RNA (rRNA) in ribosomes?

Answer 15

rRNA catalyzes peptide bond formation.

Question 16

What is the function of aminoacyl-tRNA synthetases?

Answer 16

Attach amino acids to their corresponding tRNA.

Question 17

What is the importance of the Shine-Dalgarno sequence in prokaryotes?

Answer 17

It helps position the initiator codon in the ribosomal P site.

Question 18

What initiates translation in nearly all species?

Answer 18

Methionine specified by the codon AUG.

Question 19

What is posttranslational processing?

Answer 19

Modifications after translation important for protein function.

Question 20

What are the components of a ribosome?

Answer 20

One small subunit and one large subunit made of RNA and protein.

Question 21

True or False: The genetic code is universal for all life.

Answer 21

True

Question 22

Fill in the blank: The _______ is the region in the ribosome where peptide bonds are catalyzed.

Answer 22

Peptidyltransferase center

Question 23

What is the function of initiation factors IF1 and IF2 in bacterial translation?

Answer 23

They ensure that only the initiator tRNA enters the P site.

Question 24

In bacterial cells, what allows the initiation complex to form while another process is occurring?

Answer 24

Bacterial cells lack a nucleus.

Question 25

What are the roles of eIF4A, B, and G in eukaryotic translation initiation?

Answer 25

They remove proteins and base pairings from mRNAs.

Question 26

What is the first step in eukaryotic translation initiation?

Answer 26

Initiation factors associate with the 5’ mRNA cap, 40S subunit, and initiator tRNA to make the initiation complex.

Question 27

How does the initiation complex in eukaryotes move?

Answer 27

It moves in a 5’ to 3’ manner and can unwind intramolecular base pairings.

Question 28

What codon does the initiation complex scan for during translation initiation?

Answer 28

AUG codon.

Question 29

What happens when the AUG codon is aligned with the initiator tRNA?

Answer 29

The 60S subunit joins to form the 80S ribosome.

Question 30

What is the Kozak sequence?

Answer 30

The eukaryotic version of the Shine-Dalgarno sequence.

Question 31

What starts the elongation phase of translation?

Answer 31

Initiator methionine in the P site.

Question 32

What is the ternary complex in translation elongation?

Answer 32

EF-Tu, tRNA, and an amino acid.

Question 33

What occurs when a correct tRNA matches with the mRNA codon?

Answer 33

The ribosome changes shape and ejects EF-Tu.

Question 34

What happens in the peptidyltransferase center during elongation?

Answer 34

Peptide bond transfers methionine to the amino acid in the A site.

Question 35

What does EF-G do during translation elongation?

Answer 35

Fits into the A site, causing tRNAs to move to P and E sites, and mRNA moves one codon through the ribosome.

Question 36

What triggers the termination of translation?

Answer 36

The presence of one of the three stop codons (UGA, UAA, or UAG).

Question 37

What are release factors?

Answer 37

Proteins that interact with stop codons and fit into the A site.

Question 38

What is the role of water in the termination of translation?

Answer 38

It enters the peptidyltransferase center, causing the release of the polypeptide.

Question 39

What is the definition of a genome?

Answer 39

An organism’s complete set of genetic material including all of the genes.

Question 40

What is a proteome?

Answer 40

An organism’s complete set of proteins.

Question 41

Why does the proteome produce more proteins than there are genes in the genome?

Answer 41

Due to alternative splicing and posttranslational modifications.

Question 42

What are splice variants?

Answer 42

mRNA transcripts from the same gene but with different exon combinations.

Question 43

What are isoforms?

Answer 43

Variant proteins produced from the same gene but from translation of splice variants.

Question 44

What is the role of chaperones in protein folding?

Answer 44

They participate in the folding process to achieve the native form.

Question 45

What are the two important types of chemical modifications that occur in proteins?

Answer 45

* Phosphorylation * Ubiquitination

Question 46

What is the function of kinases?

Answer 46

Enzymes that add a phosphate group to specific serine, threonine, and tyrosine amino acids.

Question 47

What do phosphatases do?

Answer 47

Remove phosphate groups from proteins.

Question 48

What is the significance of protein-protein interactions?

Answer 48

They are central to the function of large biological machines such as the replisome, spliceosome, and ribosome.

Question 49

What is ubiquitination?

Answer 49

The process that targets a protein for degradation by attaching ubiquitin.

Question 50

What is the role of signal sequences in proteins?

Answer 50

They instruct proteins where to go, such as targeting them for secretion or embedding in the cell membrane.

Question 51

What are nuclear localization sequences (NLSs)?

Answer 51

Amino acid sequences targeting proteins to the nucleus.

Question 52

Fill in the blank: Most eukaryotic proteins are _______ unless modified after translation.

Answer 52

inactive

Question 53

Fill in the blank: Posttranslational mechanisms recognize _______ in a protein sequence.

Answer 53

amino acid signatures