6. Genetics

Question 1

nucleoside

Answer 1

sugar plus base

Question 2

nucleotide

Answer 2

sugar, base, and phosphate

Question 3

pyrimidine

Answer 3

guanine and adenine

Question 4

purine

Answer 4

cytosine and thymine

Question 5

is DNA or RNA more stable?

Answer 5

DNA is more stable
strong G=C content

Question 6

hydrogen bonds
phosphodiester bonds

Answer 6

hydrogen bonds connect the strands through the bases
phosphodiester bonds are the phosphate to sugar groups

Question 7

topoisomerases

Answer 7

insert and remove supercoils

Question 8

negative supercoiling:

Answer 8

twisted in opposite sense relative to right-handed double helix; found in most cells

Question 9

DNA gyrase

Answer 9

introduces supercoils into DNA via double-strand breaks

Question 10

positive supercoiling

Answer 10

helps prevent DNA melting at high temperatures

Question 11

viruses contain either RNA or DNA genomes

Answer 11

-can be linear or circular
-can be single or double stranded

Question 12

plasmids

Answer 12

double-stranded DNA that replicate separately from chromosome
-usually circular
-generally beneficial for the cell (antibiotic resistance)
-NOT extracellular, unlike viruses
(can be lost)
plasmids are diverse- multiple can exist in one cell

Question 13

operon

Answer 13

group of genes transcribed together

Question 14

DNA replication

Answer 14

semi conservative
parent + daughter strand

Question 15

DNA polymerase I

Answer 15

fills in the gaps (bw okazaki)
removes RNA primers

Question 16

DNA polymerase III

Answer 16

replicates majority

Question 17

DNA ligase

Answer 17

reconnects broken DNA strands

Question 18

transcription in bacteria

Answer 18

produces RNA from a DNA template

mRna
tRNA
rRNA
terminator regions
RNA contains ribose
-uracil
-less stable

Question 19

polycistronic

Answer 19

multiple ribosomes reading messenger molecule
transcript for more than one gene

Question 20

RNA polymerases in bacteria archaea and eukarya

Answer 20

bacteria
-1 RNA polymerase
-only need sigma

archaea
-transcription more complex
-require other transcription factors

eukarya
-transcription more complex
-3 RNA polymerase

Question 21

sigma subunit

Answer 21

recognizes promoter sequences
binds between the -35 region and the pribnow box in the promoter sequence

Question 22

operon parts

Answer 22

promoter
5’ leader
gene 1
gene 2
gene 3
transcription terminator

go through transcription to form a polycistronic mRNA with ORF 1, 2, and 3

Question 23

transcription in bacteria: termination of RNA synthesis is

Answer 23

governed by specific DNA sequences
EX: GC-rich sequences with inverted repeat and central nonrepeating segment

rho-dependent termination

Question 24

rho-dependent termination

Answer 24

rho protein recognizes specific DNA sequences and causes a pause in the RNA polymerase, releasing RNA and RNA polymerase

Question 25

amino acids, polypeptides, and proteins

Answer 25

proteins play a major role in cell function
-catalytic proteins (enzymes)
-structural proteins (membranes, walls, ribosomes)
-regulatory proteins
proteins are polymers of amino acids
amino acids are linked by peptide bonds to form a polypeptide
proteins are one or more polypeptides

Question 26

genetic code

Answer 26

a triplet of nucleic acid bases (codon) encodes a single amino acid
-64 possible codons
-specific codons for starting and stopping translation

Question 27

degenerate code

Answer 27

multiple codons encode a single amino acid

Question 28

wobble

Answer 28

irregular base pairing allowed at third position of tRNA

Question 29

start and stop signals

Answer 29

AUG - methionine
UAA stop
UAG stop signal

Question 30

translation

Answer 30

synthesis of polypeptide directed by sequence of nucleotides in mRNA

direction of synthesis N-TERMINAL to C-terminal

Question 31

ribosome

Answer 31

site of translation
-coupled transcription/ translation in bacterial/ archaea
polyribosome- complex of mRNA with several ribosomes

Question 32

transfer RNA

Answer 32

tertiary structure due to base pairing within the tRNA molecule
-anticodon is present
–complementary to the mRNA codon
–located on the anticodon arm

Question 33

amino acid activation

Answer 33

attachment of amino acid to tRNA
-catalyzed by aminoacyl-tRNA synthetases

at least 20- each specific for a single amino acid and for all the tRNAs to which each may be properly attached (cognate tRNAs)

Question 34

elongation of the polypeptide chain consists of three phases

Answer 34

aminoacyl-tRNA binding
transpeptidation reaction
translocation

involves several elongation factors (EFs)

Question 35

tRNA binding sites of ribosome

Answer 35

aminoacyl (acceptor; A) site
-binds incoming aminoacyl-tRNA

peptidyl (donor; P) site
-binds initiator tRNA or tRNA attached to growing peptide (peptidyl-tRNA)

exit (E) site
-briefly binds empty tRNA before it leaves ribosome

Question 36

assisted protein folding and chaperones

Answer 36

chaperones catalyze macromolecular folding events

chaperones can also refold partially denatured proteins (helper proteins)

Question 37

translocases

Answer 37

transport proteins into or through bacterial and archaeal membranes

Question 38

Sec systems

Answer 38

exports unfolded proteins and inserts integral membrane proteins

Question 39

Tat systems

Answer 39

transports folded proteins through membranes

Question 40

protein secretion: sec and tat systems
-signal sequence

Answer 40

15-20 residues
found at N-terminus
signals secretory system
prevents protein from completely folding

Question 41

antibiotics that inhibit bacterial translation

Answer 41

erythromycin prevents the shift on ribosome
tetracyline blocks tRNA attachment to mRNA
chloramphenicol prevents peptide bond formation between amino acids
gentamicin and streptomycin are aminoglycosides that distort ribosome shape