DNA

Question 1

Blurt

Answer 1

DNA-double stranded
bases=adenine, cytOsine, guanine, thymine
-hydrogen bonds between complimentary base pairs
-phosphodiester bonds between phosphate group and nucleic acid of 2 nucleotides
A-T and C-G are the complimentary bade pairs
-nucleotide structure= PENTOSE SUGAR, phosphate group and a NITROGENOUS base
RNA-single stranded
-can leave nucleus
-base uracil instead of thymine so A-U

Transcription happens in nucleus, dna helicase unwinds double helix, breaks hydrogen bonds between nitrigenous bases

2 dna strand run in opposite directions?
sense and antisense strand antisense is where mRNA is tr

Question 2

what is the 3’ 5’ and 5’ 3’ direction of DNA strands?

Answer 2

sense strand=5’ 3’
-coding
-non-template
-same sequence as mRNA will have (except T not U)
-contains info for codons in mRNA
-DNA is synthesised in the 5’ 3’ direction
antisense strand= 3’ 5’
-non-coding
-TEMPLATE strand
-complimentary to sense strand
-contains code for anticodons on tRNA (again except T not U)

sense and antisense strands run antiparallel to each other

Question 3

what is the conversion of RNA to DNA

Answer 3

reverse transcription

Question 4

whatre the 3 polynucleotides that are commonly seen in this spec

Answer 4

-RNA
-DNA
-ATP

Question 5

Polynucleotides are made of many nucleotides

whatre nucleotides made of

Answer 5

mono nucleotides

Question 6

which bonds are in nucleotides and howre they formed

Answer 6

one ester bond between phosphate group and pentose sugar
one glycosidic bond between nitrogenous base and pentose sugar
2 condensation reactions required to form a nucleotide

Question 7

what does phosphodiester bond mean and what reaction are they formed in

Answer 7

sugar-phosphate

condensation

Question 8

whatre purine bases

Answer 8

double ring structure (adenine and guanine)

Question 9

whatre pYrimidine bases

Answer 9

smaller than purine, single ring (thYmine and cYtosine)

uracil is also pyrimidine

Question 10

explain complimentary base pairing

Answer 10

-a purine always pairs with a pyrimidine base
-A always pairs w T
-G always pairs w C

the base pairing makes DNA double stranded

Question 11

what will be sticking out at the end of the 5’ side?

Answer 11

a spare phosphate

Question 12

what is rRNA

Answer 12

ribosomal RNA

Question 13

stage of protein synthesis that takes place in the nucleus

Answer 13

transcription
DNA double helix unwound by DNA helicase, H bonds between bases break
mRNA attaches to template strand via complementary base pairing and RNA polymerase joins adjacent mRNA nucleotides by phosphodiester bonds
completed mRNA molecule can leave nucleus via nuclear pore

Question 14

what is the sense strand

Answer 14

“coding strand”
not directly used in transcription
other side of antisense strand
DNA not RNA
contains exact coding sequence thatll be used in protein synthesis, not complementary (bar thymine not uracil)

Question 15

which groups within amino acids bind when amino acids bind together

Answer 15

amine group of one and carboxylic group of another

forming peptide bond with loss of water

Question 16

when does DNA replication occur around mitosis

Answer 16

just before mitosis

S phase when cell isnt dividing

Question 17

how many template strands are there in DNA replication

Answer 17

2

Question 18

semi-conservative replication meaning

Answer 18

DNA molecules contain one strand of parental DNA and one newly formed complementary strand of DNA

Question 19

dispersive model DNA replication

Answer 19

-original DNA molecule breaks apart and recombines randomly before unwinding
-fragments serve as template for replication
how it was disproven: if dispersive model was true there would still only be one single band formed after each round of replication as the fragments would be recombined at random

Question 19

conservative model DNA replication

Answer 19

-one double stranded DNA molecule remains intact whilst an entirely new one is formed
-one DNA molecule of just parental strands and one of just newly synthesised strands
-one strand from each old double helix conserved in each new double helix

Question 19

why is semi-conservative replication important?

Answer 19

-genetic continuity
-reductes amount of mutations that may occur

Question 20

describe DNA replication

Answer 20

-during S phase (before mitosis)
-DNA helicase unwinds double helix
-each strand acts as a template strand
-FREE NUCLEOTIDES attracted to exposed DNA bases on template strand by DNA base pairing
-new nucleotides joined together by DNA polymerase
-OG and new strand join together by H bonding between base pairs
-new DNA molecule formed
-

Question 21

how many phosphate groups do free nucleotides have compared to normal nucleotides, what does this allow them to do?

Answer 21

free nucleotides=3
nucleotides (in DNA or RNA)=1
the extra phosphate activates the nucleotides allowing them to take part in DNA replication

DNA polymerase (catalyses reaction of forming new bonds) cleaves of extra phosphate groups to give energy to produce phosphodiester bonds between adjacent nucleotides (between phosphate group of one and deoxyribose sugar of other)

Question 22

what type of sugars are ribose and deoxyribose sugars

Answer 22

pentose

Question 23

DNA strand that DNA ribose moves in opposite direction on

Answer 23

(lagging strand) DNA ribose moves in opposite direction and can only replicate small segments of DNA at a time DNA ligase joins lagging strand segments together to form a continuous complementary strand DNA ligase forms phosphodiester bonds

Question 24

how did meselson and stahls experiment provide evidence for semi-conservative replication

Answer 24

-used heavier and lighter isotopes of nitrogen -first used bacteria containing heavier (N15), spun in centrifuge & this DNA settled at the bottom of the tube -took out some of the N15 bacteria and added to N14 bacteria -left exactly enough time for one round of DNA replication to occur -after 1 round of replication DNA molecules had exactly one strand with N15 nitrogenous bases and one with N14 so formed on band in the middle -after second round of replication the free nucleotides were coming from the bacteria still containing N14 so one lighter band and one medium band formed -medium band would get smaller as the rounds progressed as more free nucleotides are N14 and each new double strand can only contain one strand from initial double helix -this broth added to tubes and spun in a centrifuge -if conservative replication was correct then there would be 2 separate bands of DNA, one higher in the tube of lighter DNA and one lower in the tube of heavier DNA -However actual result had a single band in the middle DNA molecules now contain both N15 and N14 so settle in the middle of the tube

Question 25

good way to remember semi-conservative

Answer 25

no nucleotides created or destroyed -nothing to do with mRNA -same actual nucleotides from original double helix in new double helix, along with free nucleotides brought in by base pairing -so if different weight nucleotides brought in and DNA continues to replicate amount of N15 will decrease in the culture -free nucleotides are abundant in the nucleus, not a code being copied but nucleotides with actual complementary bases brought to template strand