DNA and RNA

Question 1

DNA and RNA is made up of …

Answer 1

Base>Scaffold>connector

Question 2

Differences between DNA and RNA is

Answer 2

• 2-deoxyribose (H instead of OH in position 2) vs ribose
• Thymine vs Uracil
• double stranded vs single stranded

Question 3

Nitrogenous bases bind to sugar at carbon position ____

Answer 3

1

Question 4

AT bp has __ bonds and GC bp has __ bonds

Answer 4

AT bp has 2 bonds and GC bp has 3 bonds (stronger)

Question 5

Bonds between sugar molecule and phosphodiester are ____while the bonds between nucleic acid pairs are ___.

Answer 5

Bonds between sugar molecule and phosphodiester are flexible while the bonds between nucleic acid pairs are fixed.

Question 6

Bases choose their position according to :

Answer 6

• Formation of optimal hydrophobic interaction between neighboured bp
• Avoiding contact with functional groups of the vincity bp

Question 7

Right-handed double helix

Answer 7

A-Form DNA and B-Form DNA

Question 8

Left handed double helix

Answer 8

Z- From DNA

Question 9

A- form DNA (Rare)

Answer 9

• right handed
• flexible but rigid DNA structure due to dehydration
• major and minor grooves can be observed in each turn
• 11 bp/helix turn
• angle between two bases: 33.1 D
• angle between bases and helix axis: 71-77 D

Question 10

B- Form DNA (common)

Answer 10

• right handed
• major and minor grooves present alternatively
• 10.4 - 10.5 bp/helix
• angle between two bases: 35.9 D
• angle between bases and helix axis: 90 D
• narrower than A DNA

Question 11

Z- Form DNA

Answer 11

• left handed
• zigzag appearance
• recognition for binding of regulator proteins
• 12 bp/ helix turn
• angle between two bases: 60 D

Question 12

What is positive supercoiling?

Answer 12

Positive supercoiling is over- wounded DNA.

• more than 10.4 bp/turn (increase in linking number)
• More difficult to separate the DNA

Question 13

What is negative supercoiling?

Answer 13

Negative supercoiling is under-wounded DNA

• less than 10.4bp/turn (decrease in linking number)
• easier to separate DNA

Question 14

Topoisomerase I

Answer 14

• break one DNA strand, pass other strand though gap and reseal the nick
• ATP not required

Question 15

Topoisomerase II

Answer 15

• break both DNA strands
• energy required (ATP or NADH)
• Gyrase (in bacteria)

Question 16

Gyrase

Answer 16

Gyrase is Top II in bacteria which introduce negative supercoil

Question 17

What is hyperchromicity?

Answer 17

Hyperchromicity is increase in UV light absorption (260nm) in single stranded DNA than double stranded DNA

• H-bond limits the resonance of the aromatic ring and limit the absorbance
• hypochromic effect depends on GC content of DNA

Question 18

What is Tm?

Answer 18

Tm is temp at which 50% of the DNA strand is separated

Question 19

How is DNA denatured?

Answer 19

• separate H-bond by heating or base addition

Question 20

How is DNA renatured?

Answer 20

1. Nucleation: paired nucleotide sequence sequence meet each other
2. fast reestablishment of double strand

Question 21

Velocity of DNA renaturation/ reassociation depends on. __

Answer 21

1. concentration of cations to mask the negative charges of the phosphorus-group
2. temp (optimal ~25 D celcius)
3. size and concentration of DNA

Question 22

How many bp in human genome?

Answer 22

3000 million bp

3* 10^9

Question 23

Louis Pasteur

Answer 23

Life only develops only out of life

Question 24

Gregor Mendel

Answer 24

the law of heredity

Question 25

Ernst Haeckel

Answer 25

the nucleus is responsible for heredity

Question 26

Friedrich Miescher

Answer 26

discover that DNA is nucleus

Question 27

Griffith Avery, MaCarty and MacLeod

Answer 27

DNA could transform one type of bacteria into another type of bacteria

Question 28

Chargaff

Answer 28

Analyzed the relative amount of A,C,G, T in cells | - found A=T, C=G

Question 29

Hershey and Chase

Answer 29

DNA, not protein is the infectious agent in viruses | - T2 phage , DNA is labeled with 32P and Protein is labeled with 35S

Question 30

Watson and Chase

Answer 30

X-ray diffraction photo of DNA, double helix discovery

Question 31

Meselson and Stahl

Answer 31

Semi-conservative model of DNA replication (one new strand pair with one old strand) - bacteria cultured in heavy nitrogen (15N) medium then transferred to light nitrogen (14N) then centrifuged DNA sample

Question 32

What are 3 possible DNA replication mechanism?

Answer 32

Conservative model Dispersive model Semiconservative model

Question 33

Conservative model

Answer 33

the parental strand remain intact and a second new double strand is made

Question 34

Dispersive model

Answer 34

daughter strand contains segments of parental strand and segments of newly synthesised strand

Question 35

Semiconservative model

Answer 35

daughter strand consist of one new strand and one parental strand (each parental strand is used as template)

Question 36

What are two ways to prove semi-conservative model?

Answer 36

- culturing bacteria in heavy nitrogen medium and then transferring to light nitrogen medium and centrifuging the DNA sample - sister chromatid staining (sister chromatid exchange and BrdU)

Question 37

Sister chromatid exchange

Answer 37

the exchange of genetic material between two identical sister chromatids