Lecture 16-18

Question 1

Where is the genetic information of most living organisms stored

Answer 1

in deoxyribonucleic acid (DNA)

Question 2

In some viruses, where is genetic material present

Answer 2

in ribonucleic acid (RNA)

Question 3

What are nucleic acids composed of

Answer 3

nucleotides

Question 4

What are the components of a nucleotide

Answer 4

nitrogen-containing bases
sugar (pentose)
phosphate (phosphodiester bond)

Question 5

What is the difference between a ribose and a deoxyribose sugar

Answer 5

on carbon two a hydroxyl is seen in a ribose
on carbon two a hydrogen is seen in a deoxyribose (loss of the oxygen molecule)

Question 6

What are purines

Answer 6

adenine and guanine

Question 7

What are pyrimidines

Answer 7

cytosine thymine and uracil

Question 8

What bond joins nucleotides

Answer 8

phosphodiester

Question 9

Where does the phosphodiester bond connects two sugars

Answer 9

connects C3 of one to the C5 of the other

Question 10

What is Chargaffs rule

Answer 10

purines = pyrimidines

Question 11

%A = what

Answer 11

%T

Question 12

%G = what

Answer 12

%C

Question 13

How much of DNA is made up of purines

Answer 13

50%

Question 14

How much of DNA is made up of pyrimidines

Answer 14

50%

Question 15

How many H bonds are formed between A and T

Answer 15

2

Question 16

How many H bonds are formed between C and G

Answer 16

3

Question 17

With more G-C bonds, what occurs with melting point

Answer 17

melting point increases, more bonds to break

Question 18

What are restriction enzymes and how are they used

Answer 18

group of endonucleases produced in bacteria as a means of destroying foreign DNA, by cleaving DNA at restriction sites
- restriction sites are often palindromic
- sticky ends are cut horizontally, blunt ends are cut vertically (refer to slide 25 for a visual)

Question 19

What three components are required by a cloning plasmid

Answer 19

a multiple cloning site (MCS), an origin of replication, and a selectable marker

Question 20

What are the four steps of cloning plasmids

Answer 20

digestion: restriction enzymes form complementary sticky ends
ligation: DNA fragment and plasmid join at sticky ends and form phosphodiester bonds to close the nicks
transformation: the ligated plasmid is mixed with bacterial cells under given conditions to optimize transformation
selection: cells containing the plasmid will grow on plates and form colonies

Question 21

What is PCR and how does it work

Answer 21

polymerase chain reaction
step 1: denaturation of protein to split strands apart
step 2: primer annealing
step 3: polymerases attach and elongation occurs by replication of strands

Question 22

What is the pattern in PCR production

Answer 22

2^(number of cycles) = number of copies

Question 23

How does a forward primer work

Answer 23

anneals to the BOTTOM strand and has the same sequence as the top strand

Question 24

How does a reverse primer work

Answer 24

anneals to the TOP strand and has the same sequence as the bottom strand

Question 25

In vivo and in bacteria/viral DNA, what is the coiling pattern

Answer 25

supercoiled

Question 26

What type of enzyme seals the nicks in DNA

Answer 26

ligase

Question 27

How many approximate domains are the circular DNA molecules segregated into

Answer 27

50 domains

Question 28

What is more extensive about human DNA structure

Answer 28

eukaryotes have very large genomes, so the DNA must be extensively folded and packaged into multiple chromosomes

Question 29

What does each eukaryotic chromosome consist of

Answer 29

large linear molecule of DNA
large amounts of 2 protein types; 5 histones and many non-histone proteins
*essentially chromatin = DNA + histones + protein

Question 30

Why are histones important to DNA

Answer 30

DNA is very negative and histones are very positive

Question 31

What is the first level of DNA packaging in chromatin

Answer 31

nucleosomes
- DNA wraps around histones to form nucleosomes (11nm) (DNA wraps around histones 1 and 3/4 rotations)
- the segments not wrapped around histones, between nucleosomes, are called “linker DNA”

Question 32

What does the nucleosome core consist of

Answer 32

octamer of histones (4 types of histone, 2 of each)

Question 33

What is a complete nucleosome made up of (not just the core)

Answer 33

octamer of histones, histone H1 (fifth histone that acts as the glue), and wrapped DNA

Question 34

What is the second level of DNA packaging in chromatin

Answer 34

30 nm chromatin fiber
- the scrunching together of the string of nucleosomes within a 30 nm width

Question 35

What is the third level of DNA packaging in chromatin

Answer 35

inter-phase chromosomes
- 30 nm chromatin fibres are tethered to the chromosome scaffold (non histone proteins)