protein synthesis and selection Flashcards
Compare and contrast DNA in eukaryotic cells ( DNA in mitochondria/chloroplasts) and DNA in prokaryotic cells.
Comparisons:
1.Both haveNucleotides that have identical structures (deoxyribose/phosphate/nitrogenous base);
2.both haveNucleotides joined by phosphodiester bonds;
Contrasts:
:4.Eukaryotic nuclear DNA is longer than prokaryotic DNA;
5.Eukaryotic nuclear DNA contain introns, WHEREAS prokaryotic DNA does not;
6.Eukaryotic nuclear DNA is linear, WHEREAS prokaryotic DNA is circular;
7.Eukaryotic nuclear DNA is associated with histones, WHEREAS prokaryotic DNA is not;
Compare and contrast DNA and (mature) mRNA
Comparisons:
Both are polymers made from single monomers called nucleotides
Both made from nucleotides linked by phosphodiester bonds
contrasts:
DNA is double stranded whereas RNAis single stranded
DNA is longer whereas RNA is shorter
Thymine in DNA whereas replaced with uracil in RNA
Deoxyribose in DNA whereas ribose in mRNA
DNA has hydrogen bonds whereas mRNA doesnt have hydrogen bonds
DNA has introns whereas mRNA doesnt have introns
Compare and contrast tRNA and mRNA
Comparisons:
Both are polymers made from single monomers called RNA nucleotides
Both are single stranded
Both made from nucleotides linked by phosphodiester bonds
Both contain Uracil, guanine, cytosine and adenine (and also ribose sugar)
Contrasts:
mRNA has codons whereas tRNA has a single anticodon
mRNA is linear whereas tRNA has a clover-leaf shape
mRNA has no hydrogen bonds whereas tRNA does have hydrogen bonds
mRNA is longer (can be different lengths depending on the gene) whereas tRNA is shorter (always the same length)
Describe transcription.
1.DNA Helicase breaks hydrogen bonds
so strands separate;
2.Only one DNA strand acts as template;
3.RNA nucleotides complimentary base pair with template ;
4.according to base pairing rule; Adenine-Uracil, Cytosine-Guanine:
5.RNA polymerase joins adjacent RNA nucleotides together forming phosphodiester bonds through condensation reactions;
6.Pre-mRNA spliced to remove introns in eukaryotes
Describe translation.
- Ribosome binds to mRNA at start codon;
- Ribosome binds with two codons.
- tRNA with 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
Why is the genetic code described as being:
1.Universal
2.Non-overlapping
3. Degenerate
1.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
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
Define gene mutation
Change in the DNA nucleotide sequence on DNA resulting in the formation of a new allele.
Explain why a mutation may not affect the protein structure?
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)
Explain how a mutation can have a positive affect?
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.
Define the following mutations and describe how they can lead to a non-functional protein
-Substitution
-Addition
-Deletion
Substitution: a change to a single base in the DNA base sequence of a gene - mutation causes change in triplet so triplet codes for different amino acid.
-change 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.
Addition: an addition of a single base in the DNA base sequence of a gene
Deletion: a deletion of a single base in the DNA base sequence of a gene
-changes triplets after mutation (frame shift
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;
Describe stabilising selection
-Selection against both extremes
-Only mean phenotype has increased reproductive success (survival/ability to reproduce and find a mate)
-Alleles for mean phenotype are passed on to future generations in greater numbers.
-Over time, frequency of mean alleles, coding for mean phenotype, INCREASES.
-Alleles coding for both extreme phenotypes decrease.
occurs with no change in environment
Describe directional selection
-Selection for only one extreme
-Individuals with advantageous allele have increased reproductive success (survival/ability to reproduce and find a mate)
-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 the other extreme phenotype decreases within the population.
occurs when there is a change in the environment
what enables natural selection
genetic diversity
