2.3.1 DNA - deoxyribonucleic acid

Question 1

shape of DNA molecule

Answer 1

double helix (due to coiling of 2 sugar-phosphate backbone strands)

Question 2

monomer

Answer 2

molecule that repeats to become a monomer eg. amino acids are monomers of proteins & nucleotides are monomers of nucleic acids

Question 3

nucleotide

Answer 3

molecule consisting of 5-carbon sugar, phosphate group & nitrogeneous base

Question 4

polynucleotide

Answer 4

large molecule containing many nucleotides

Question 5

describe positioning of nitrogenous base & phosphate group on nucleotides

Answer 5

• nitrogeneous base linked to C1 of sugar
• phosphate group linked to C5 or C3
  —> via covalent bonds formed from condensation reactions

Question 6

properties of nucleotides

Answer 6

• monomers of nucleic acids, DNA & RNA
• in RNA pentose sugar = ribose
• in DNA = deoxyribose
• phosphorylated nucleotides contain 1+ phosphate group (eg. ADP, ATP)

Question 7

ATP

Answer 7

adenosine triphosphate

Question 8

ADP

Answer 8

adenosine diphosphate

Question 9

where is DNA found

Answer 9

• nuclei of all eukaryotic cells
• in cytoplasm of prokaryotic cells
• inside some types of viruses

Question 10

structure of DNA molecule

Answer 10

• polymer (monomeric units = nucleotides)
• 2 polynucleotide strands which run in opposite directions (antiparallel)
• each DNA nucleotide = phosphate group, 5-carbon sugar (deoxyribose) & 1 of 4 nitrogenous bases (A, G, T or C)
• covalent bond between sugar & phosphate group = phosphodiester bond

Question 11

when are phosphodiester bonds broken/made

Answer 11

broken = when polynucleotides break down
formed = when polynucleotides are synthesised

Question 12

how many types of nucleotides does DNA consist of

Answer 12

4

Question 13

purine

Answer 13

adenine or guanine = 2 rings

Question 14

pyrimidine

Answer 14

thymine or cytosine (1 ring)

Question 15

what are the 2 antiparallel DNA strands joined by

Answer 15

hydrogen bonds between nitrogeneous bases

Question 16

adenine pairs with…
how many H bonds

Answer 16

thymine
2 hydrogen bonds

Question 17

guanine pairs with…
how many H bonds

Answer 17

cytosine
3 hydrogen bonds

Question 18

what does a purine always pair with

Answer 18

pyrimidine

Question 19

why does a purine always pair with a pyrimidine

Answer 19

• gives equal sized ‘rungs’ on DNA ladder
  —> can twist into double helix (coil)
  = stability to molecule

Question 20

what to hydrogen bonds allow

Answer 20

allow molecule to unzip for transcription & replication

Question 21

what is the upright part of the large DNA molecule (resembling a ladder) formed by

Answer 21

formed by sugar-phosphate backbones of antiparallel polynucleotide strands

Question 22

describe the 5’ end of the antiparallel sugar-phosphate backbone

Answer 22

phosphate group is attached to 5th carbon atom of deoxyribose sugar

Question 23

describe the 3’ end of the antiparallel sugar-phosphate backbone

Answer 23

phosphate group attached to 3rd carbon atom of deoxyribose sugar

Question 24

what do the rungs of the ladder consist of

Answer 24

complementary base pairs joined by h bonds

Question 25

is the antiparallel sugar-phosphate backbone stable

Answer 25

yes

Question 26

what's protected within the antiparallel sugar-phosphate backbone

Answer 26

integrity of the coded info within the base sequence

Question 27

how is DNA organised in eukaryotic cells

Answer 27

- majority of DNA content/genome is in nucleus - each large molecule of DNA is tightly wound around special histone proteins into chromosomes --> each chromosome = 1 molecule of DNA - loop of DNA (without histone proteins) inside mitochondria & chloroplasts

Question 28

how is DNA organised in prokaryotic cells

Answer 28

- DNA is in loop & within cytoplasm (not enclosed in nucleus) - not wound around histone proteins (naked)

Question 29

draw structure of ATP

Answer 29

- 3 phosphate - ribose sugar - adenine --> check pg. 86 of OCR textbook

Question 30

draw structure of ADP

Answer 30

--> check pg. 86 of OCR textbook