protein synthesis and selection Flashcards
(18 cards)
why is the genetic code described as being:
universal
non overlapping
degenerate
the same triplet / codon codes for the same amino acid in all organisms
each base is part of only one triplet
more than one triplet/codon for the same amino acid
suggest one advantage of showing the genetic code as base sequences on mRNA rather than triplets on DNA
DNA has two strands each with a different base sequence
describe transcription
DNA Helicase breaks H Bonds so strands separate
Only one DNA strand acts as a template
RNA nucleotides are attracted to exposed bases according to base pairing rule : adenine uracil , guanine cytosine by H Bonding
RNA Polymerase joins free adjacent RNA nucleotides together forming phosphodiester bonds through condensation reactions
Pre mRNA spliced to remove introns in eukaryotes
compare and contrast tRNA and mRNA
Comparisons
both are polymers made from single monomers called RNA nucleotides
both are single stranded
both are made nucleotides linked by phosphodiester bonds
both contain uracil guanine cytosine and adenine (also ribose sugar)
Contrasts
mRNA is linear whereas tRNA has a clover lead shape
mRNA has no hydrogen bonding where tRNA does have H bonding
mRNA is longer(can be different lengths depending on gene) where tRNA is shorter(always same length)
mRNA has codons whereas tRNA has a single anticodon
describe translation
ribosome binds to mRNA at start codon
ribosome binds with two codons
tRNA complementary anticodons bind with codon
formation of peptide bond between amino acids using energy from ATP
tRNA released as ribosome moves along mRNA to the next codon
Ribosome releases polypeptide into rough endoplasmic reticulum when the STOP codon is reached
compare and contrast DNA and mature mRNA
both are polymers made from single monomers called nucleotides
both are made from nucleotides linked by phosphodiester bonds
DNA is double stranded whereas RNA is single stranded
DNA is longer whereas RNA is shorter
Thymine in DNA whereas replaced with uracil in RNA
Deoxyribose in DNA whereas ribose in RNA
DNA has hydrogen bonding whereas RNA doesnt have H bonding
DNA has introns whereas mature mRNA doesn’t have introns
define substitution mutation and how it can lead to a non functional protein
a change or swap to the single base in the DNA base sequence of a gene (single point mutation)
affect: mutation causes change in triplet so triplet codes for amino acid
[changes in amino acid sequence( primary structure)
forms ionic hydrogen disulphide bonds between r groups in different places
changes tertiary structure of protein so non functional]
define addition mutation and describe how it can lead to a non functional protein
an addition of a single base in the DNA base sequence of a gene (frame shift)
affect: changes triplets after mutation (frame shift)
[changes in amino acid sequence( primary structure)
forms ionic hydrogen disulphide bonds between r groups in different places
changes tertiary structure of protein so non functional]
define deletion mutation and describe how it leads to a non functional protein
a deletion of a single base in the DNA base sequence of a gene (frame shift mutation)
affect: changes triplets after mutation (frame shift)
[changes in amino acid sequence( primary structure)
forms ionic hydrogen disulphide bonds between r groups in different places
changes tertiary structure of protein so non functional]
define gene mutation
change in the DNA nucleotide sequence on DNA resulting in formation of a new allele
explain why a mutation may not affect the protein structure
genetic code degenerate so amino acid sequence may not change
or
mutation is intron so amino acid sequence may not change
(does change amino acid but no effect on tertiary structure
new allele is recessive so doesn’t influence phenotype)
explain how a mutation can have a positive affect
mutation causes change in amino acid sequence
changes tertiary structure of polypeptide
that gives positively changes the properties resulting in an increased reproductive success/ increased survival
describe stabilising and directional selection
stabilising: selection against both extremes
directional: selection for only one extreme
describe the principles of natural selection
[named example] variation due to mutation
[named] different environmental/ abiotic/ biotic conditions/ selection pressures
selection for advantageous allele [that leads to named advantage]
differential reproductive success- organisms with advantageous allele/ features breed and transfer their alleles to the next generation at a higher rate
leads to increase in allelic frequency over a long period of time
what is the function of a stop codon
stop translation - resulting in detachment of polypeptide chain from ribosome
what can using a dilution too low to count the number of bacteria lead to
the count being unlikely to be reproducible and accurate
as there will be too many cells so they will be overlapping
what can using a dilution too high to count the number of bacteria lead to?
the original dilution being so diluted that there will be no remaining bacteria present to see
a^c = b -> loga b=c
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