6) Nucleic Acids & Protein Synthesis Flashcards
what are the 3 components of a nucleotide ?
- nitrogenous base
- pentose sugar (deoxyribose/ribose)
- phosphate group
what are the 3 components of ATP?
- adenine
- ribose
- phosphate (3)
what bases are purines and what are pyrimidines?
purines (bigger) - adenine & guanine
pyrimidines (smaller) - thymine/uracil & cytosine
what structure do purines have compared to pyrimidines ?
purines (bigger)- double ring structure
pyrimidines (smaller)- single ring structure
how many hydrogen bonds are there between adenine and thymine ?
2
how many hydrogen bonds are there between guanine and cytosine ?
3
which bases pair with which ?
A - T
G - C
describe the structure of DNA
- double helix
- antiparallel strands
- 5’ to 3’ & 3’ to 5’ (opposite strand)
what bonds link the nucleotides
phosphodiester bonds
give 3 differences between the structure of DNA & RNA
DNA
- v long strands
- sugar is deoxyribose
- bases are A, T ,C ,G (no U)
- 2 polynucleotide strands
RNA
- short strands
- sugar is ribose
- bases are A, U, C, G (no T)
- single polynucleotide strand
what is the function of helicase
unwinds the double helix at replication forks
function of primase
synthesises the RNA primer
function of DNA polymerase III
synthesises the new strand of DNA by adding ACTIVATED nucleotides onto the primer in a 5’ to 3’ direction
- forms phosphodiester bonds
function of DNA polymerase I
removes the primer & replaces it with DNA
- forms phosphodiester bonds
function of DNA ligase
joins the ends of DNA and Ozaki fragments ON LAGGING STRAND
- forms phosphodiester bonds between fragments
explain the leading strand
Dna polymerases can move in the same direction as the replication fork so replication is continuous.
explain the lagging strand
DNA polymerases have to move in the opposite direction to the replication fork, so replication is discontinuous.
what is a gene ?
a sequence of nucleotides that code for a polypeptide
whats a universal code
almost every organism uses the same code - same codons code for the same amino acids in all living things
whats a degenerate code
multiple codons coding for the same amino acids
whats a gene mutation
change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide
What are the 3 ways a gene mutation can be caused by?
- substitution
: (best case) degenerate, as even if base changes = same amino acid.
: (worst case) 1 amino acid changes
= whole protein.
: worse if stop codon changes - deletion (non-functional protein)
- insertion (non-functional protein)
outline the stages of transcription
- DNA unwinds by RNA polymerase
- H bonds break
- one strand acts as template
- RNA polymerase recognises and binds to the promoter
- RNA polymerase adds RNA nucleotides to exposed DNA strands.
- phosphodiester bonds formed
- product = messenger RNA
describe the role of tRNA in protein synthesis
- tRNA carries amino acid to rbisomes.
- each type of tRNA carries specific amino acid.
- anticodon on tRNA binds to codon on mRNA.
- tRNA holds amino acids in place.
- tRNA molecules reused
how is the length of RNA molecule shortened
- introns are removed (splicing)
- exons are joined together (primary transcript)
outline the stages of translation
- mRNA used as template
- mRNA translated 5’ to 3’ direction
- binding of ribosome to mRNA
- first TRNA binds to start codon
- second tRNA binds to ribosome
- mRNA read in base triplets
- tRNA bring amino acids
- peptide bonds btwn amino acids
- reach a stop codon
