1.3 biological molecules 2

Question 1

describe the structure of a nucleotide

Answer 1

• contains a 5 carbon pentose sugar
• contains a base that is either purine (2 rings) or pyrimidine (1 ring)
• contains a phosphate group, which make the molecule slightly negative

Question 2

describe how a nucleotide is formed and the reactions involved

Answer 2

• the base is on top and joins with the sugar through a condensation reaction to form a glycosidic bond
• the sugar joins with the phosphate group in a condensation reaction to form an ester bond

Question 3

how is energy supplied to the cell

Answer 3

• the third phosphate group in ATP is broken in a hydrolysis reaction
• this leaves in inorganic phosphate group
• two further bonds are made to make ADP and the stable phosphate group which releases energy

Question 4

describe the structure of ATP

Answer 4

• the base joined to the sugar by a glycosidic bond and the sugar also joined to the phosphate groups by ester bonds
• three phosphate groups

Question 5

what are nucleic acids made of

Answer 5

• they’re made of chains of nucleotides joined together by condensation reactions that result in phosphodiester bonds
• bonds form between the sugar and phosphates of nucleotides and the bases stick out

Question 6

what is the difference between RNA and DNA

Answer 6

• RNA is single stranded and DNA is double stranded

Question 7

how is the DNA double strand held together

Answer 7

held together by the hydrogen bonds between complementary bases

Question 8

what are the complementary bases and state whether they are purine or pyrimidine

Answer 8

PURINE (2 rings) PYRIMIDINE (1 ring)
adenine thymine
guanine cytosine

Question 9

describe the phosphate sugar back bone of a poly nucleotide

Answer 9

the two strands are called the 5 prime and the three prime as on one side the phosphate group is connected to carbon no. 5 and on the other, it is connected to carbon n0. 3

Question 10

why is ATP a better energy source than glucose

Answer 10

• when getting energy from ATP, energy is released in small manageable quantities (less waste)
• it takes a single reaction to produce ATP (quick)
• it is an immediate source of energy
• the bonds in ATP are of higher energy

Question 11

describe the theories of Watson and Crick and the steps of experiment carried out by Meselson and Stahl

Answer 11

• theorised semi conservative DNA replication, that only one of the DNA strands in conserved
  1. bacteria was grown in a culture containing heavy nitrogen (N15), as the DNA contains nitrogen in its bases
  2. sample of the bacteria grown was spun in a centrifuge and those containing heavy nitrogen were extracted
  3. the extracted bacteria were then grown in a broth containing lighter nitrogen (N14)
  4. the bacteria was then spun in a centrifuge and the bacteria that replicated once, were extracted

Question 12

what were the potential results of the experiment carried out by Meselson and Stahl

Answer 12

• if conservative DNA replication had occurred then then template DNA molecules would only contain nitrogen 15 and the new molecules in the broth would only contain nitrogen 14
• if semi conservative DNA had occurred then all of the DNA molecules would contain both nitrogen 15 and nitrogen 14

Question 13

how does DNA make copies of itself

Answer 13

1. the original DNA molecule unwinds along the line of hydrogen bonds
2. DNA helicase causes the strands to separate
3. free nucleotides in the nucleoplasm are attracted to the complementary base pairs
4. new hydrogen bonds form between base pairs, DNA polymerase catalyses the linking of the nucleotides to one of the separated strands
5. DNA ligase catalyses the formation of phosphodiester bonds

Question 14

what are the signals that codons can code for

Answer 14

• start and stop signals

Question 15

how many bases are needed to code for 15 amino acids

Answer 15

15 X 3 = 45

Question 16

what does it mean that the genetic code in non-overlapping

Answer 16

each base is only read once in what codon its in

Question 17

define codon and anticodon

Answer 17

codon - a triplet of bases in mRNA
anticodon - the tRNA molecules that transfer amino acids that are complementary to the codons on mRNA

Question 18

what does it mean that the genetic code is degenerate
why is it an advantage ?

Answer 18

• it contains more information than needed, there are often multiple ways you can code for one amino acid
• this limits the effects of mutations because sometimes even if a mutation occurs, it will not change which amino acid is produced

Question 19

what is the sense strand and what is the antisense strand

Answer 19

• the sense strand is the coding strand
• the anti sense strand is the template strand

Question 20

describe how mRNA is formed

Answer 20

• forms on the template of the anti sense strand in the nucleus
• parts if the DNA molecule unravel
• the complementary RNA bases to the DNA strand from the cytoplasm
• RNA polymerase catalyses the formation of the phosphodiester bonds between the sugars and the phosphate group

Question 21

describe the shape/ structure of a tRNA molecule

Answer 21

• has three bases (anticodon) that match the genetic code for DNA ad corresponds to an amino acid
• the shape of the molecule is a result of the hydrogen bonding
• each of the molecules has a binding site where it picks up the particular amino acid

Question 22

stopped at protein synthesis