dna structure

Question 1

antiparallelel

Answer 1

-side by side but in opposite directions

Question 2

which ends have free hydroxyl vs phosphate groups on them

Answer 2

-5’ end has a free phosphate groupe and 3’ end has free hydroxyl

Question 3

H bonds between bases

Answer 3

-thymine and adenine have 2h bonds between them
-cytosine and guanine have 3h bonds between them

Question 4

T or F: one turn of the helix occurs every 5 base pairs

Answer 4

f, every 10 base pairs

Question 5

purines and pyrimidines

Answer 5

pure as gold (pureines- adenine guanine)
cut the py (oyrimidines=cystosine, uracile thymine)
-a pairs w t
-c pairs w g

Question 6

t or f; dna from a single diploid human cell extends in a single thread for almost 2 meters long

Answer 6

t

Question 7

are histones charged?

Answer 7

yes positively charged

Question 8

t or f: You could fit 25,000 strands of
DNA side by side in the width of
a single adult hair

Answer 8

t

Question 9

origin of replication

Answer 9

dna sequence where replication is initiated
–replication bubble is formed (each bubble has 2 replication forks)
–a eukaryotic chromosome may may have thousands of replication origins

replicatiob begins at specififc sites where the two parental strands seperate and form replication bubbes. eventually the replication bubbles fuse and synthesis of he dauhgter strands in complete

Question 10

Dna replication is _____________ (one strand si from parental dna and other s newly synthesized daughter strand)

Answer 10

semi-conservative

Question 11

how many origins of replication do bacterial chromosomes have?

Answer 11

one origin. replication proceeds 5’->3’ in both directions

Question 12

how many origins of replication in eukaryotes?

Answer 12

multiple origins of replication (proceeds in 5’ to 3’ from each starting point)

Question 13

mechanism of DNA replication

Answer 13

• the initial nucleotide strand is an RNA primer
  -Rna primase synthesizes primer on DNA strand
  -DNA replication is catalyzed by dna polymerase III which needs an rna primer
  -dna polymerase I replaces rna primer w dna nucleotides
  -dna polymerases add nucleotides to 3’ end of growing strand. *synthesis of new strand is 5 to 3’. reads template strand 3 to 5’

Question 14

dna helicase

Answer 14

unwinds the double helix by breaking h bonds between strands

Question 15

single stranded dna binding proteins

Answer 15

prevent dna strands from rejoining after helicase seperates strands

Question 16

rna primase

Answer 16

catalyzes the synthesis of short rna primers

Question 17

dna polymerase III

Answer 17

extends the strand from primer in the 5-3 direction; also has proofreading activity

Question 18

dna polymerase I

Answer 18

degrades rna primers and replaces it with dna nucleotides. synthesized in 5’-3- direction. also has proofreading activity

Question 19

dna ligase

Answer 19

joins the short dna fragments on lagging srand (okazaki fragments) into a continuous strand (introduces phosphodiester bond between two fragments)

Question 20

leading strand vs lagging strand

Answer 20

leading strand=continuous synthesis
laggging strand=disc synthesis