Nucleic acids

Question 1

what is the structure of nucleotides?

Answer 1

• monomers from which nuclei acids are made

Question 2

describe the differences between DNA and RNA nucleotides?

Answer 2

• pentose sugar: deoxyribose in DNA and ribose in RNA
• Bases: adenine, thymine, guanine and cytosine in DNA, adenine, guanine, uracil and cytosine.
  -mainly involved in: storage of genetic information for DNA, protein synthesis for RNA.
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Question 3

what are purines?

Answer 3

Bases with a double-ring structure e.g. adenine and guanine

Question 4

what are pyrimidines?

Answer 4

bases with a single-ring structure e.g. thymine and cytosine

Question 5

the structure of DNA

Answer 5

• Consists of two polynucleotide strands (the back bone) that are anti-parallel (in opposite directions)
• complementary base pairs in the centre held by hydrogen bonds
• C and G form 3 hydrogen bonds
  -A and T form 2hydrogen bonds
• proportion of A and T and G and C are the same

Question 6

how are polynucleotides formed?

Answer 6

when a phosphodiester bond is formed in a condensation reaction between the phosphate group of one nucleotide and the the hydroxyl group on the pentose sugar of the other nucleotide

Question 7

structure of ADP and ATP

Answer 7

phosphorylated nucleotides meaning they contain more than one phosphate group so are comprised of a pentose sugar (ribose), a nitrogenous base (adenine) and inorganic phosphates.

Question 8

describe how DNA replicates?

Answer 8

• DNA helicase uncoils the structure the double helix structure by breaking the hydrogen bonds between the strands
  -each strand act as a template
• free nucleotides from the cytoplasm joins to the template in complementary base pairs
• DNA polymerase joins the the nucleotides forming phosphodiester bonds forming a new sugar-phosphate backbone
  -semi-conservative replication

Question 9

describe the practical investigations into the purification of DNA

Answer 9

• first crush the piece of fruit using a pestle and mortar this help break down the cellulose cell wall
  -add detergent this dissolves the cell surface membrane
  -add protease enzyme which break down the histogram proteins associated with DNA
  -filter to remove solids
• add salt to help the DNA clump together
  -pour cold alcohol into the mixture as DNA is insoluable in alcohol so should float to the top of

Question 10

genes

Answer 10

• a section of DNA that codes for the sequence of amino acids in a polypeptide

Question 11

the nature of the genetic code

Answer 11

• near universal: in almost all living organisms the same triplet of DNA bases codes for the same amino acids
• degenerate: for all amino acids except methionine and tryptophan, there is more than one base triplet which can code for the base this reduce the effect of mutations as a change is one base of triplets could produce another base triplet that still codes for the same amino acids
• non-overlapping: each triplet is not read more than once

Question 12

transcription

Answer 12

the process of making MRNA from a DNA template

Question 13

describe the process of transcription

Answer 13

• DNA helicase breaks the hydrogen bonds between the strands
• complementary RNA nucleotides join with the bases of the exposed nucleotides
• the mRNA molecule is a copy of DNA strand
  -RNA polymerase joins the RNA nucleotides forming phosphodiester bonds.
• MRNA is produced and moves out of the nucleus through the nuclear pore

Question 14

codon

Answer 14

​A sequence of three bases (triplets) on mRNA that codes for a specific amino acid.

Question 15

translation

Answer 15

the formation of a protein, at ribosomes

Question 16

describe the stages of translation

Answer 16

• MRNA attaches to a ribosome that is made up of two subunits of rRNA
• TRNA molecule with a anticodon complementary to the start codon attaches binds to the MRNA by complementary base pairing
• another tRNA molecule attaches itself to the next codon on the MRNA.
• peptide bond is formed between the amino acids on the first and second tRNA molecule catalysed by an enzyme
• the first tRNA molecule moves away leaving the amino acid behind
• a third tRNA molecule binds to the next codon and its amino acid binds to the first 2. the 2nd tRNA molecule moves away
• process of ribosome moving along the mRNA continues producing a polypeptide chain. until stop codon is reached
• polypeptide chain moves away from the ribosome

Question 17

evidence for semi-conservative replication

Answer 17

• scientist in 1958 grew ecoli in N15. most of DNA in the bacteria was heavy
• then transferred the bacteria into a medium containing N14 and was left for long enough to undergo one replication, from this a hybrid DNA was produced.
• Bacteria divided once more this produced one hybrid strand and one light showing DNA is semi-conservative,

Question 18

why is it important that DNA replication is accurate?

Answer 18

• to make sure the genetic information is conserved each time the DNA is replicated

Question 19

Why is DNA replication considered semi- conservative

Answer 19

The new DNA molecule contains one strand of the original DNA and one strand of the new DNA. The original strand acts as a template for new strands

Question 20

What is a allele

Answer 20

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Different versions of a gene