DNA

Question 1

nucleotide

Answer 1

monomer from which nucleic acids are formed

Question 2

what does each nucleotide comprise ?

Answer 2

a pentose, a phosphate group and a purine or pyrimidine base

Question 3

what are the two types of nucleic acids ?

Answer 3

DNA ( deoxyribonucleic acid ) and RNA ( ribonucleic acid )

Question 4

Structure of nucleotides

Answer 4

each nucleotide consists of three substances combined together:
- a pentose
- nitrogenous base
- phosphoric acid

Question 5

nitrogenous base

Answer 5

• a double ringed purine (either adenine or guanine) - in both DNA and RNA
• a single ringed pyrimidine (either cytosine or thymine) - DNA
  (either cytosine or uracil)

Question 6

polynucleotide chains

Answer 6

two nucleotides can be joined together by a condensation reaction catalysed by an enzyme DNA polymerase
- formation of a covalent bond, called a phosphodiester bond

Question 7

how does DNA polymer occur in pairs ?

Answer 7

joined by hydrogen bonds between bases - creates a double helix

Question 8

nucleotide + nucleotide =

Answer 8

dinucleotide

Question 9

how do polynucleotides form ?

Answer 9

large numbers of nucleotides become condensed together to form huge molecules

Question 10

how do backbone of the polynucleotide form ?

Answer 10

alternating sugar and phosphate molecules

Question 11

where can hydrogen bonds only form ?

Answer 11

between complementary base pairs
- cytosine and guanine
- adenine and thymine

Question 12

what is RNA ?

Answer 12

a polymer of a nucleotide formed ribose, a nitrogenous base and a phosphate group

Question 13

what are the nitrogenous bases in RNA ?

Answer 13

adenine, guanine, cytosine and uracil

Question 14

Pyrimidines

Answer 14

single stranded structure
- cytosine and thymine

Question 15

purines

Answer 15

double ringed structure
- guanine and adenine

Question 16

what are the three types of RNA ?

Answer 16

messenger RNA
transfer RNA
ribosomal RNA

Question 17

messenger RNA

Answer 17

carries a copy of a single gene to a cells ribosomes

Question 18

transfer RNA

Answer 18

carries individual amino acids to ribosomes during protein synthesis

Question 19

ribosomal RNA

Answer 19

forms part of the sub units of ribosomes

Question 20

what does DNA only use ?

Answer 20

A, T , C and G

Question 21

bonding - RNA molecules

Answer 21

• base + sugar joins with a glycosidic bond
• the phosphate + sugar joins an ester bond
• both require condensation reaction to occur

Question 22

in every DNA nucleotide:

Answer 22

• pentose is deoxyribose
• the base is cytosine, guanine, adenine, or thymine, but never uracil

Question 23

complementary base pairing

Answer 23

leads to:
- stability of the DNA double helix
- transfer of genetic information from DNA to RNA
- the way amino acids are assembled into polypeptides in the cytoplasm

Question 24

A joins with what

Answer 24

T

Question 25

C joins with what

Answer 25

G

Question 26

the bases of two strands fit together only if:

Answer 26

the deoxyribose molecules to which they are attached point in opposite directions

Question 27

which directions do the sugar phosphate backbones ?

Answer 27

opposite directions - strands are antiparallel

Question 28

Semi conservative replication - step 1

Answer 28

the double helix of the DNA molecule unwinds and the hydrogen bonds holding the strands together break - causes the bases on each strand to become exposed catalysed by the enzyme DNA helicase

Question 29

Semi conservative replication - step 2

Answer 29

- both exposed strands now acts as a template for the production of the new polynucleotide strand - free nucleotides are attached to the exposed complementary bases -DNA polymerase links the adjacent nucleotides forming phosphodiester bonds - the sugar phosphate backbone

Question 30

Semi conservative replication - step 3

Answer 30

- DNA is replicated in segments - DNA ligase joins the segments together - condensation reaction - forms phosphodiester bonds

Question 31

Semi conservative replication - step 4

Answer 31

two identical DNA molecules are formed - semi conservative replication because each strand contains 1 copy of the original DNA

Question 32

Genetic code

Answer 32

major role: enable a cell to make specific proteins - large DNA molecule codes for a large number of proteins

Question 33

gene

Answer 33

a sequence of bases which code for specific amino acids in a polypeptide chain

Question 34

what is a genetic code ?

Answer 34

a combination of three nucleotide base triplets encodes an individual amino acid - each combination of base triplets encodes the same amino acid in all organisms

Question 35

what is universal ?

Answer 35

triple code

Question 36

With four bases, how many different combinations can be made ?

Answer 36

64 (4x4x4)

Question 37

how many amino acids are commonly used by cells ?

Answer 37

20 - there is many more different and DNA base triplet combinations than are needed to encode 20 amino acids

Question 38

degenerate

Answer 38

some amino acids are encoded by more than one base triplet

Question 39

genetic code

Answer 39

1. it has one 3 base start codon = TAC 2. it has 3 different 3 base stop codons = ATT, ATC and ACT 3. 3 bases code for a specific amino acid

Question 40

why is the genetic code non overlapping ?

Answer 40

each triplet only read once and triplets don't share any bases