Chromosome structure

Question 1

Function of genetic material

Answer 1

must replicate, control growth & development of the organism, and allow the organism to adapt to changes in the environment

Question 2

Griffiths experiment

Answer 2

virulent bacteria kill mice, non virulent bacteria do not. Heat killed virulent bacteria do not kill mice but mixture of heat killed virulent and living non virulent kill the mouse
Transformation occurred - live, non-virulent strain picked up free DNA from dead virulent strain

Question 3

Avery MacLeod McCarty experiment

Answer 3

using same heat killed virulent and live non-virulent strains, they treated mixtures of both with an RNAse, a protease and a DNAse (respectively)
RNAse and protease yielded virulent bacteria where the DNAse did not because it broke down the free DNA in the solution so the non-virulent bacteria could not take it up

Question 4

In some viruses the genetic info is in the RNA. True or false

Answer 4

TRUE

Question 5

3 subunits of DNA

Answer 5

the sugar (pentose), phosphate group and nitrogenous base

Question 6

4 nitrogenous bases

Answer 6

2 purines (adenine and guanine) and 2 pyrimidines (cytosine & thymine)

Question 7

How can DNA and RNA be differentiated

Answer 7

Ribose has an OH at the 2 carbon where deoxyribose only has a H

Question 8

Nucleotides are linked by a phosphodiester bond, which is?

Answer 8

Links 3’ C of one sugar to 5’ C of another

Question 9

Chargaffs rule

Answer 9

amount of purines = amount of pyrimidines (%A = %T, %G = %C) in organisms
Adenine and thymine are complementary, guanine and cytosine are complementary
A and T form 2 H bonds and G and C form 3 H bonds

Question 10

William Atsbury found that DNA was a polymer of stacked bases. True or false?

Answer 10

TRUe

Question 11

Rosalind Franklin took an X-ray crystallography picture of DNA, showing that it is a double helix, what did this show?

Answer 11

Two strands have opposite chemical polarity (3 to 5)

Question 12

Molecular hybridization

Answer 12

a probe binds to genetic material and acts as a beacon to indicate where a chromosome, gene, or RNA molecule is in a cell

Question 13

Gel Electrophoresis

Answer 13

DNA loaded into gel made of polyacrylamide or agar and migrate across agar based on charge (towards positive pole), larger samples stop sooner, smaller samples go far

Question 14

Restriction Enzymes (RE)

Answer 14

group of endonucleases produced in bacteria as a means of destroying foreign DNA, cleave DNA at restriction sites

Question 15

Cloning plasmids have 3 identifiable markers, what are they

Answer 15

MCS, ORI (origin of replication which enables plasmid replication in host cells), and a selectable marker (e.g. antibiotic resistance)

Question 16

Multiple Cloning Site (MCS)

Answer 16

region with many restriction sites into which exogenous DNA is inserted (in a bacterial plasmid usually)

Question 17

Digestion, ligation, transformation, selection

Answer 17

plasmid & foreign DNA are cleaved with RE forming sticky ends

DNA fragments & plasmid hybridize at sticky ends. DNA ligase forms phosphodiester bonds to seal nicks in each strands

ligated plasmid is mixed with bacterial cells under conditions to optimize transformation. Plasmid replicates within host cells as cellular machinery recognizes the ORI within the plasmid.

only cells containing the plasmid will grow on antibiotic-containing plates (in this case, ampicillin), forming colonies which all have the plasmid.

Question 18

Polymerase Chain Reaction (PCR)

Answer 18

Denaturation -DNA double strand is separated by 95ºC temperature

Primer annealing- specific primers engineered that are complementary to the 2 strands
DNA replicates 5’ to 3’ so primers need to be specific in direction & order
Forward primer - anneals to bottom strand and has same sequence as top strand
Backward primer - reverse of above

Elongation - DNA polymerase duplicated template DNA at 72ºC
72ºC is still quite high, that’s why Taq DNA polymerase (enzyme from thermophilic bacteria) is used for this
At every round, amount of DNA doubles - 2, 4, 8, 16, 32, etc

Question 19

Next Generation Sequencing

Answer 19

genomic DNA to be sequenced is first fragmented, then adaptor sequences are added to each fragment, then fixed to solid surface (microchip or silicone bead)
PCR is then used to amplify each fragment so that each bead contains thousands of copies of the same fragment

Question 20

Super-coiled (chromosomes)

Answer 20

multiple rotations of circular DNA (think of twisting an elastic) which allows it to become very compacted. (with the help of RNA and proteins)

Question 21

Haploid DNA of humans is 3.3 x 10^9 nucleotides (1000x larger than bacteria)
true or false

Answer 21

TRUEE

Question 22

A chromosome is one long linear molecule of DNA and it contains 2 types of proteins, which are?

Answer 22

Histones and non-histone proteins, since histones are positively charge they attract negative DNA

Question 23

Chromatin

Answer 23

DNA + histones + protein

Question 24

How many levels of organization does chromatin have

Answer 24

3

Question 25

Nucleosomes (level of organization)

Answer 25

core is octamer of histones, 146 bp of DNA wrapped, 1.75 turns/nucleosome

Linker DNA (between nucleosomes) varies in length from 8-114 bp
Nucleosomes are 11 nm wide - must take up more space but more material is fit in
Essentially a greater efficiency of space than small but spread out uncoiled DNA

Question 26

30 nm chromatin fibre (organization)

Answer 26

less elegant compaction, just scrunching of nucleosomes

Question 27

Interphase chromosomes (organization)

Answer 27

DNA is tethered to non-histone protein scaffold

Structure is 300 nm overall until chromosome goes into metaphase chromosome