Year 12 - Protein synthesis and selection Flashcards
Compare and contrast DNA in prokaryotic and eukaryotic cells
Compare:
- Both have nucleotides with identical structures
- Both have phosphodiester bonds
- DNA in mitochondria/chloroplast same as DNA in prokaryotes
Contrast:
- Eukaryotic DNA is longer than prokaryotic DNA
- Eukaryotic DNA has Introns vs no Introns
- Eukaryotic DNA is linear vs prokaryotic DNA is circular
Eukaryotic histones vs prokaryotic no histones
Compare and contrast DNA and mRNA
Compare:
- polymers of nucleotides
- both have phosphodiester bonds
Contrast:
- Double vs Single stranded
- Longer vs Shorter
- Thymine vs Uracil
- Deoxyribose vs Ribose
- Hydrogen bonds vs no hydrogen bonds
- Introns vs no introns
Compare and Contrast mRNA and tRNA
Comparisons:
- Polymers made of RNA nucleotides
- Single stranded
- Joined by phosphodiester bonds
- Uracil, guanine, cytosine and adenine
Contrasts:
- mRNA codons vs tRNA anticodons
- mRNA linear vs tRNA clover leaf
- mRNA hydrogen bonds vs tRNA no H bonds
Describe transcription.
- DNA helicase breaks hydrogen bonds so strands separate
- Only one DNA strand acts as a template
- RNA nucleotides are attracted to exposed bases
- according to base pairing rules; Adenine-Uracil, Cytosine-Guanine
- RNA polymerase joins adjacent RNA nucleotides in condensation reactions forming phosphodiester bonds
- Pre-mRNA spliced to remove introns (eukaryotes)
Describe translation.
- Ribosome binds to mRNA at start codon
- Ribosome binds with two codons
- tRNA with complementary anticodon binds with codons
- formation of peptide bonds between amino acids using ATP
- tRNA released as ribosome moves along mRNA to next codon
- Ribosome releases polypeptide into RER when stop codon is reached
Describe the principles of natural selection.
(Contextualise variation, allele, selection pressures)
1. Variation in population due to a mutation causing formation of new allele
2. Different selection pressures
3. Selection for advantageous allele (name advantage)
4. Differential reproductive success - organisms with advantageous allele breed and transfer their alleles to the next generation at a higher rate
5. Leads to increase in allelic frequency over a long period of time
Describe stabilising selection
- Selection against both extremes
- Only mean phenotype has increased reproductive success
- Alleles for mean phenotype are passed on to future generations
- Over time, frequency of the mean allele, coding for mean phenotype, increases
- Alleles coding for both mean phenotypes decrease
Describe Directional selection
- Selection for only one extreme
- Individuals with advantageous allele have increased reproductive success
- Alleles for one extreme are passed on to future generations in greater numbers
- Over time, frequency of this extreme allele, coding for extreme phenotype, increases
- Alleles coding for other extreme phenotype decreases withing the population.
Define gene
A sequence of DNA nucleotide bases that codes for a polypeptide
Why is the genetic code described as being:
1.Universal
2. Non-overlapping
3. Degenerate
Suggest one advantage of showing the genetic code as base sequences on mRNA, rather than triplets on DNA.
- The same triplet/codon codes for the same amino acid in all organisms. (don’t need to write but note it does not say same ‘triplets code for an amino acids’)
- each base is part of only one triplet.
- more than one triplet/codon for the same
amino acid - DNA has two strands each with a different base sequence
- Define gene mutation
- Explain why a mutation may not affect the protein structure?
- Explain how a mutation can have a positive affect?
- Change in the DNA nucleotide base sequence on DNA resulting in the formation of a new allele.
- -Genetic code is degenerate so amino acid sequence may not change
-OR Mutation is in an intron so amino acid sequence may not change
(-Does change amino acid but no effect on tertiary structure
-New allele is recessive so does not influence phenotype) - -Mutation causes change in amino acid sequence.
- change tertiary structure of polypeptide.
- that gives positively changes the properties resulting in an increased reproductive success/increased survival.
