module 2.1.3 - nucleotides and nucleic acids

Question 1

what are the 3 components of a nucleotides

Answer 1

a phosphate group, a pentose sugar and an organic nitrogenous base

Question 2

what are the purine bases (2 rings) in RNA and DNA

Answer 2

adenine and guanine for both RNA and DNA

Question 3

what are the pyrimidine bases (1 ring) in RNA and DNA

Answer 3

cytosine and uracil in RNA
cytosine and thymine in DNA

Question 4

what are the pentose sugars in RNA and DNA

Answer 4

ribose in RNA and deoxyribose in DNA

Question 5

what are the 3 types of RNA

Answer 5

messenger RNA, transfer RNA and ribosomal RNA

Question 6

what does mRNA do

Answer 6

it carries the copy of the gene out of the nucleus and transfers it to the ribosomes where the code is for protein synthesis

Question 7

what does tRNA do

Answer 7

it transports amino acids to the ribosomes

Question 8

what does rRNA do

Answer 8

it make up the ribosomes

Question 9

what is the structure of RNA

Answer 9

it is a polynucleotide, non - helical, usually single stranded and much shorter than DNA
bases are complementary: adenine to uracil (2 H bonds), cytosine to guanine ( 3 H bonds)

Question 10

what is the structure of DNA

Answer 10

it is found in the nucleus. the 2 polynucleotide strands lies in opposite directions (anti-parallel) and are joined together to form double helix. each purine is paired to a pyrimidine

Question 11

what is the structure of ATP and ADP

Answer 11

they both contain a pentose sugar (ribose), a nitrogenous base (adenine)
ADP has 2 phosphate groups but ATP has 3 phosphate groups

Question 12

what is a polynucleotide and how is it formed

Answer 12

formed when nucleotides bind together in a long chain
- the bonds are formed by condensation and are called phosphodiester bonds. they can be broken by hydrolysis
- these bonds form between the sugar of one nucleotide and the phosphate group of another, making a sugar–phosphate ‘backbone’
- leaves the organic base of each nucleotide sticking out to the side of the chain

Question 13

explain the process of semi conservative replication

Answer 13

1. one double-stranded molecule untwists and the hydrogen bonds between the base pairs break —-> catalysed by the enzyme helicase
2. the two polynucleotide chains separate, exposing the bases
3. each strand is then used as a template to make two new double strands
4. new nucleotides pair to the exposed bases on both strands, using their complementary shapes to pair correctly
   5 each new chain of nucleotides is bonded together by the enzyme DNA polymerase to form the second half of each DNA molecule
5. the enzyme also checks that the pairing of the bases is correct
6. each new molecule then twists to form its double helix

Question 14

what is a mutation

Answer 14

when an incorrect base may be bonded into place

Question 15

what is the pattern of mutation

Answer 15

random and spontaneous

Question 16

what are 3 consecutive bases called and what does it code for

Answer 16

triplet and codes for 1 amino acid

Question 17

what is a degenerate codon

Answer 17

amino acids that coded for by more than 1 triplet

Question 18

how many possible triplet codes are there

Answer 18

64

Question 19

from this point, what is the process of protein production

Answer 19

a sequence of amino acids forms one polypeptide
- the length of DNA that codes for one polypeptide is called a gene
- one gene codes for one polypeptide. This may form a protein
- if the protein contains more than one polypeptide (i.e. it has a quaternary structure), there will be more than one gene used to code for the protein

Question 20

what are the 2 stages of polypeptide synthesis

Answer 20

transcription and translation

Question 21

what happens in the first one (not description, definition)

Answer 21

reading the code and producing a messenger molecule to carry the code out to the cytoplasm

Question 22

what happens in the second (not description, definition)

Answer 22

converting the code to a sequence of amino acids

Question 23

describe what happens during transcription

Answer 23

The genetic code is held in the nucleus. The DNA molecule is too large to leave the nucleus, so a smaller messenger molecule is made called messenger RNA (mRNA). The double-stranded DNA molecule is unwound and split by the action of the enzyme RNA polymerase, which breaks the hydrogen bonds holding the two strands together. This exposes the sequence of bases in the gene. The coding strand carries the genetic code and the complementary strand is a non-coding strand sometimes called the antisense strand or the template strand, which is used to build a copy of the coding strand called messenger RNA (mRNA). It has an identical sequence of bases to the coding strand of the gene, except that the thymine is replaced by uracil. Each triplet of bases on the mRNA is called a codon. The enzyme RNA polymerase joins the bases of the RNA to produce a complete single-stranded molecule. The base pairing is given in the table.

The molecule of mRNA detaches from the DNA template and the DNA strands can rejoin to remake the double helix. The mRNA leaves the nucleus via the nuclear pores and enters the cytoplasm

Question 24

describe what happens during translation

Answer 24

translation is the conversion of the genetic code to a sequence of amino acids. the mRNA joins on to a ribosome in the cytoplasm (ribosomes consist of ribosomal RNA associated with enzymes). the ribosome contains enough space for two codons at a time. the mRNA slides through the groove between the two components of the ribosome. as each codon enters the ribosome, it is used to position the next amino acid. amino acids must be activated — they are combined with a specific molecule of transfer RNA (tRNA) that has a specific base triplet called the anticodon. the anticodon of the tRNA is complementary to a codon on the mRNA. ATP is used in this activation process. the amino acids attached to tRNA molecules are aligned with the correct part of the mRNA by the complementary pairing of the bases in the codon and anticodon. enzymes bind the amino acids together in a chain by condensation reactions to create a growing polypeptide chain. the tRNA molecule is then released to be reused. when the ribosome reaches the end of the mRNA, the complete polypeptide chain is released and folds to form the secondary and tertiary structure of the protein. some proteins need to be activated by cyclic AMP (cAMP), which interacts with the new protein to alter its three-dimensional shape. this makes the protein a better shape to fit their complementary molecules