bio objectives chapter 13

Question 1

calculate the percent bases in a DNA strand if given the percentage of one (apply)

Answer 1

CHARGAFFS RULES:
A and T bases are equal
C and G bases are equal

Question 2

Describe structure of DNA strand

Answer 2

sugar-phosphate backbone
nitrogenous bases are on interior
purine and pyrimidine - width compatible with x ray

Question 3

Explain why A pairs to T and C pairs to G

Answer 3

combinations allow them to form hydrogen bonds - one purine and one pyrimidine in each base pair

Question 4

Outline the steps of DNA replication

Answer 4

1) semiconservative model - one old parent strand, and one new strand

Question 5

first step dna replication

Answer 5

begin: origins of replication
- 2 DNA strands are separated opening a replication bubble
- long DNA - multiple bubs
- end of bubble is replication fork - parental strands are unwound

Question 6

2nd step: synthesizing new DNA strand

Answer 6

proteins needed
helicases : enzymes that untwist DNA parent strand
single strand binding proteins - bind to and stabilize single-strand DNA
primase: encode DNA parental strand to make RNA primers
IMPORTANT: Topoisomerase: relieves the strain caused by tight twisting ahead of the replication fork by breaking, swiveling, and rejoining DNA strands

Question 7

Purpose of DNA polymerase

Answer 7

catalyzes the elongation of new DNA at a replication fork -
adds nucleotides at the ending of 3 chain added with sugar and 3 phosphate groups
- loses 2 phosphate groups

Question 8

Compare and contrast how the leading and lagging strand are synthesized

Answer 8

leading strand: nucleotides added towards replication fork
lagging strand: nucleotides added away from replication fork

Question 9

Compare and contrast how the leading and lagging strand are synthesized:

Answer 9

1) DNA poly 3 adds nucleotides to primer: okazaki fragment 1
2) RNA primer meets fragment - DNA pol3 detaches
3) fragment 2 primed. DNA pol 3 adds DNA - detatches meeting one primer
4) SNA pol 1 replaces RN with DNA adding nucleotides to three

Question 10

telomeres:

Answer 10

prevent shortening of DNA molecules , DO NOT postpone

Question 11

DNA packing:

Answer 11

DNA is wrapped around histones
Nucleosome: DNA bead wound twice around protein core of 8 histones - tight loop of DNA and and protein
INTERPHASE - nucleosomes is packed in as chromatin
30 nanometers fiber: nucleosome packing
metaphase chromosome: densely packed DNA

Question 12

Analyzing and engineering genes

Answer 12

DNA cloning: identical copies of DNA - ex bacteria contains plasmids
Restriction enzymes to make recombinant DNA - acterial restriction cut DNA and adds DNA from other sources

Question 13

PCR steps:

Answer 13

Denaturation: separate DNA
Annealing: DNA primers to end of strand
Extension: DNA polymerase extends primers