Molecular Biology-DNA Structure

Question 1

purines

Answer 1

G, A: double rings

Question 2

pyrimidines

Answer 2

C, T, U: single rings

Question 3

nucleoside

Answer 3

ribose or deoxyribose with a purine or pyrimidine linked to the 1’ carbon

Question 4

nucleotides=nucleoside triphosphates

Answer 4

phosphate esters of nucleosides, with 1-3 phosphate groups joined to the ribose ring of the 5’ hydroxy group

Question 5

what is the backbone of DNA?

Answer 5

the sugar/phosphate portion, this is the portion of DNA that is invariant

Question 6

how are nucleotides in the DNA chain?

Answer 6

by covalent phosphodiester bonds between the 3’ hydroxy group of one deoxyribose and the 5’ phosphate group of the next deoxyribose

Question 7

oligonucleotide

Answer 7

a polymer of several nucleotides linked together

Question 8

polynucleotide

Answer 8

a polymer of many nucleotides

Question 9

what’s the convention of writing nucleotide sequence?

Answer 9

5’ to 3’

Question 10

Watson-Crick model

Answer 10

cellular DNA is a right-handed double helix held together by hydrogen bonds between bases

Question 11

A bonds to:

Answer 11

T with two hydrogen bonds

Question 12

G bonds to:

Answer 12

C with three hydrogen bonds

Question 13

two chains of DNA are complementary if:

Answer 13

each strand can hydrogen bond when the strands are oriented in an antiparallel fashion

Question 14

annealing/hybridization

Answer 14

the binding of two complementary strands of DNA into a double-stranded structure

Question 15

melting/denaturation

Answer 15

the separation of DNA strands

Question 16

right-handed double helix

Answer 16

corkscrews in a clockwise motion

Question 17

what stabilizes the double helix?

Answer 17

van der Waals interactions between the bases stacked upon each other

Question 18

genome

Answer 18

the sum total of an organism’s genetic information

Question 19

chromosome

Answer 19

each piece of ds-DNA

Question 20

what composes prokaryotic (bacterial) genomes?

Answer 20

a single circular chromosome

Question 21

is there a correlation between genome size and evolutionary sophistication?

Answer 21

no

Question 22

DNA gyrase

Answer 22

an enzyme in prokaryotes that uses ATP energy to twist the gigantic circular molecule to make it more compact and sturdy; breaks the DNA and twists the two sides of the circle around each circle to result in a twisted circle composed of ds-DNA to create supercoils

Question 23

supercoil

Answer 23

coils of a structure that is already coiled

Question 24

how is eukaryotic DNA packaged?

Answer 24

wrapped around globular proteins (histones) and further compacted/condensed

Question 25

nucleosome

Answer 25

"beads" of DNA wrapped around an octamer of histomes

Question 26

chromatin

Answer 26

fully packed DNA, composed of closely stacked nucleosomes

Question 27

heterochromatin

Answer 27

darker and denser regions of chromosomes; rich in repeats

Question 28

euchromatin

Answer 28

less dense region of chromosomes

Question 29

density of DNA indicates:

Answer 29

extent of coiling or compactness, patterns are constant and heritable

Question 30

lighter/less dense regions have:

Answer 30

higher transcription rates and higher gene activity because loose packing=DNA more accessible to enzymes and proteins

Question 31

centromere

Answer 31

the region of the chromosome to which spindle fibres attach during cell division

Question 32

kinetochores

Answer 32

multiprotein complexes that act as anchor attachment sites for spindle fibers

Question 33

what are centromeres made of?

Answer 33

heterochromatin and repetitive DNA sequences

Question 34

centromere position defines the ratio between:

Answer 34

the p and q arm

Question 35

p arm

Answer 35

short

Question 36

q arm

Answer 36

long

Question 37

what are the four centromere positions?

Answer 37

metacentric, submetacentric, acrocentric, telocentric

Question 38

telomeres

Answer 38

the ends of linear chromosomes, distinct nucleotide sequences repeated 50-hundreds of times

Question 39

what is the typical telomere sequence in vertebrates?

Answer 39

5'-TTAGGG-3' (guanine rich)

Question 40

specialized telomere caps

Answer 40

distinguish telomeres from double-stranded breaks (because telomeres can be single or double-stranded) and prevents activation of repair pathways

Question 41

what is the function of telomeres?

Answer 41

to prevent chromosome deterioration and also prevent fusion with neighbouring chromosomes

Question 42

how come prokaryotes do not have telomeres?

Answer 42

because circular DNA has no "end"