L3. DNA & chromosomes

Question 1

explain the bond between C and G

Answer 1

• triple hydrogen bond
• tight
• harder to dissociate

Question 2

explain the bond between A and T

Answer 2

• double hydrogen bond
• loose
• easier to dissaociate

Question 3

what is coding DNA

Answer 3

DNA that codes for proteins

Question 4

what is non-coding DNA (“junk DNA”)

Answer 4

• DNA that does not encode for proteins
• they instead encode for functional RNA

Question 5

what is a genome

Answer 5

• total genetic information carried by all chromosomes
• includes coding and non-coding DNA

Question 6

explain genomic size

Answer 6

• the size is the number of nucleotides or base pairs
• the size does not correspond to the number of genes or the complexity of the organism

Question 7

explain eukaryotic chromosomes in a diving cell vs a nondividing cell

Answer 7

• dividing cell: chromosomes become condensed as the sister chromatids become apart and then they become visible
• nondividing cell: when dyed, DNA is seen all throughout the nucleus

Question 8

explain the chromosomes during interphase

Answer 8

the cell grows and the chromosomes duplicate

Question 9

explain the chromosomes during mitosis

Answer 9

the cell divides and each cell has a set of chromosomes

Question 10

explain how the DNA looks during interphase

Answer 10

as it is being replicated, DNA is pulled apart for easier access for replication

Question 11

define chromatid

Answer 11

one of the two identical halves of a chromosome that has been replicated in preparation for cell division

Question 12

what is euchromatin

Answer 12

a chromosomal region that is spread out an is easily accessible for proteins

Question 13

what is heterochromatin

Answer 13

a chromosomal region that is condensed and is not easily accessible for proteins

Question 14

how does Polymerase Chain Reaction work

Answer 14

1. Heat up DNA and design primers that will bind to the DNA
2. Add an enzyme that normally copies DNA itself and it will instead copy the DNA in the reaction
3. Overtime it will give you a DNA product of the sample you are interested in
4. Sequence the copied DNA to see the actual piece of DNA with its nucleotides

Question 15

what must you know for Polymerase Chain Reaction work

Answer 15

a particular region of DNA and how many of each nucleotide is within the DNA region

Question 16

what are restriction enzymes

Answer 16

they are enzymes that cleave off different parts of DNA

Question 17

explain the process of agarose gel electrophoresis

Answer 17

• Apply a current to agarose gel, DNA will naturally sink through DNA
• Shorter DNA: goes through the gel quickly and will be at the bottom
• longer DNA: slower to get through the gel and we at the top

Question 18

explain fluorescent in situ hybridization

Answer 18

1. Take RNA or DNA and hybridize it. Then you can label it with a fluorescence tag
2. Take a whole tissue and treat it under certain conditions so that it opens RNA or DNA
3. Add a probe to the tissue and you will be able to see where the contemporary region is

Question 19

what is a karyotype

Answer 19

an individual’s complete set of chromosomes

Question 20

how can karyotypes be seen in fluorescence in situ hybridization

Answer 20

• you can label each gene or chromosome with a fluorescent tag and see where they are
• can then see alterations in chromosomes such as deletion or addition which are associated with certain disorders or conditions

Question 21

what are nucleosomes

Answer 21

• they are basic structural unit of DNA packaging in eukaryotes
• they exist to tighten and condense the packaged DNA

Question 22

explain the structure of the nucleosome

Answer 22

• it is composed of DNA wrapped around a set of eight proteins called histones
• they have tails sticking out from histones

Question 23

what it the difference between chromatin and a nucleosome

Answer 23

• chromatin are thread-like stained bodies with repeating units of nucleosomes
• looks like a bead on a string under the microscope

Question 24

nucleosome - what are linker histones

Answer 24

• they are histones that help pull nucleosomes together
• H1 and H5

Question 25

nucleosome - explain the tails

Answer 25

• enzymes will come and modify the tails
• these modifications dictates how tight or loose the DNA is wound

Question 26

nucleosome - what are chromatin remodeling complexes

Answer 26

they are multiprotein complexes that use the energy of ATP hydrolysis to mobilize and restructure nucleosomes

Question 27

nucleosomes - what are the core histones

Answer 27

histone H2A, H2B, H3, and H4

Question 28

nucleosomes - explain how modifications can affect how tightly DNA is wound

Answer 28

• if methionine is on the histone tails: DNA is more tightly wound and the gene is silenced
• if acetylation is on the histone tail: DNA is more loosely wound and the gene will be expressed