Protein Synthesis + Selection Flashcards
Structural Differences between DNA and mRNA
DNA double stranded whereas mRNA is single
DNA has deoxyribose whereas mRNA ribsie
DNA is longer whereas mRNA is shorter
DNA has hydorgen bonds whereas mRNA does not
DNA has introns whereas mRNA does not
DNA has thymine whereas in mRNA thymine replaced w uracil
Mrna
Single stranded
Complementary copy of a single gene from template strand of DNA
No introns
Where does transcription occur in eukaryotes
Nucleus
Where does transcription occur for prokaryotes
Cytoplasm
Introns
Non coding sequences within a gene of DNA
Exons
Coding regions within a gene of DNA
Where does translation occur
Cytoplasm of ribosome
Chromosome non disjunction
Pair of homologus chromosomes fail to separate during metaphase 1
Or
Sister chromatids fail to separate during metaphase 2
Stabilising selection
Occurs in populations where environment stable
2 extremes
Favours average
Eliminates extreme
Reduces variability and evolutionary change
Define Silent mutation
• A mutation that results in no change of the phenotype/amino acids
Because genetic code degenerate
Consequence there no mixing between different population of the same species
Small gene pool
Feature of bacteria that makes them a good organism to study natural selection
Fast growth rate
How and why is the agar plate sterilised
HOW
• Agar boiled
WHY
•Prevent growth of unwanted microorganisms/ prevent contamination
Group of compounds on the multodisk
Antibiotics
Disease resistance benefits farmers because
• Less crop is lost to disease
• so higher profit
How does artificial selection affect genetic diversity
• Smaller gene pool
• Because through artificial selection, some alleles have been chosen
Explain how selection occurs in living organisms
• Variation due to mutation
• selection pressure ( the thing that is causing the organism to change)
• selection for advantageous allele
• reproductive success/ selected organisms survive and reproduce
• leads to change in allelic frequency
What is a mutagenic agent and examples
An environmental factor that can increase the rate of mutation
• Dna reactive chemicals such as benzene,bromine
• Biological agents such as bacteria and viruses
Mutations also result in genetic diversity
Disruptive selection
Favours 2 extreme phenotypes
Least common but most important for evolution
Features of the genetic code
• Non overlapping- each triplet is only read once
• Degenerate- more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids)
• universal- the same bases and sequences code for amino acids in all organisms
Ways in which DNA in a chloroplast is different from DNA in the nucleus
• DNA shorter
• fewer genes
• DNA circular not linear
• Not associated with histones
• does not contain introns
State what a gene codes for (2)
• the amino acid sequence of a polypeptide
• A functional Rna producf
The 2 non-coding regions of eukaryotic nuclear DNA are
• Introns
• Multiple repeats
Why is it possible for a gene from one organism to be introduced into and function in a different organism
• Genetic Code is universal
Compare the DNA in prokaryotic cells and the nucleus of eukaryotic cells
SIMILARITIES
• Nucleotide structure is identical (both have phosphate,deoxyribose and base)
• Nucleotides joined by phosphodiester bond
• Both prokaryotic and nuclear eukaryotic DNA are made of triplet codons
• Both double stranded
• Both helical
DIFFERENCES
• Prokaryotes have short DNA whereas eukaryotes have long DNA
• Prokaryotes have circular DNA whereas eukaryotes have linear dna
•Prokaryotic DNA are not associated with histones whereas eukaryotic DNA are
• Prokaryotic DNA do not have non-coding regions of DNA whereas eukaryotic DNA have introns and multiple repeats
Regions of introns do not change in frequency at the same rate of exons because
• Introns do not code for proteins
• So there is no selection pressure
A dinucleotide and a base pair differ because
• A dinucleotide contains a phosphodiester bond
• A base pair between (adenine-thymins/cytosine-guanine) forms 2/3 Hydrogen bonds
Suggest one advantage of showing the genetic code as base sequences on mRNA, rather than triplets on DNA.
-Ribosomes assemble polypeptides using mRNA
-DNA has 2 strands each with a different base sequence
Stop codons result in (whatever the stop codon is in the question
Stopping of translation
Resulting in polypeptide chain into the RER
More Copies of the gene (say the gene that is in the question)
• More transcription of that gene so more translation so faster reaction
If an organisms resistance to something has not decreased( the one given in the question)
This is because
• no selection pressure against it
• The organism ( the one given in the question) has reproduced passing on the alleles for resistance
Differences between DNA and RNA
DNA has deoxyribose, thymine, and is double-stranded contains hydrogen bonds and introns whereas RNA has ribose, uracil, and is single-stranded and does not contain hydrogen bonds or introns
Not all mutations result in a change to the amino acid sequence of the encoded polypeptide. Explain why.
(Genetic) code degenerate / Mutation in intron
Describe transcription
Dna helicase breaks hydrogen bonds between complementary bases so strands separate
Only one DNA strand acts as a template
Rna nucleotides attracted to exposes bases
Attraction according to base pairing rule A-U C-G
Rna polymerase joins RNA nucleotides forming phosphodiester bonds through condensation reactions
Pre mrna splices to remove introns
Describe what happens during alternative splicing
Selecting different combinations of splice sites within Mrna
Structural Differences between Mrna and Trna
-no base pairing in mRNA
-mRNA is linear whereas Trna has a cloverleaf shape
-mRNA has no binding site whereas Trna does (for amino acids)
-mRNA is different for each gene whereas all tRNAs are same length
• Trna has hydrogen bonds whereas
Mrna doesn’t
tRNA has anticodons whereas mRNA has codons
Give one difference between transcription in prokaryoric and eukaryotic cells
• In prokaryotic cells, transcription happens in the cytoplasm and produces mRNA, no splicing
• In eukaryotic cells, transcription happens in the nucleus and produces pre-MRNA needs ti be spliced
During alternative splicing
• Introns are removed from pre-mrna strands
• exons are joined together to form the final mrna strand
Describe the function of ribosomes in protein synthesis
•Translation of polypeptide
•Mrna attaches to ribosome
•Idea of 2 binding sites
•Two amino acids are held close together
•Ribosome catalyses formation of peptide bonds in a condensation reaction(Trna holds these structures in place)
• allows Assembly of amino acids into the sequence
Explain the role of Trna in translation
•Trna attaches to specific amino acid
• Trna with amino acid move to ribosome
•Anticodon of Trna complementary to Codon of mRNA and binds to it
Describe how a gene codes for a polypeptide
• Gene has a specific base sequence
• The Dna base sequence determines the base sequence on mRNA and therefore mRNA base sequence determines the sequence of amino acids in the polypeptide
• 3bases=1triplet
Explain how the organic bases help to stabilise the structure of DNA
Hydrogen bonds between the base pairs holds two strands together
Many hydrogen bonds provides strength
Describe translation
mRNA binds to ribosome
Ribosome finds start codon
Idea of 2 codons
Allows tRNA carrying specific amino acid with complementary anticodon to bind to codon
Catalyses formation of peptide bonds between Aa using energy from ATP
tRNA released as ribosome moves along
Ribosome releases polypeptide into RER when stop codon reached
Translation
mRNA associates with ribosome
Ribosome finds start codon
tRNA brings specific amino acid
Anticodon on tRNA complementary to codon on mRNA
Catalyses formation of peptide bonds between amino acids using energy from ATP
tRNA release as Ribosome moves along codon
Ribosome released into RER once stop codon reached
Where does strand separation of DNA occur
Nucleus
Which part of cell cycle is gene mutation likey to occur and why
Interphase/S-phase
Longest stage and where dna replication occurs
Give 2 factors other than cost that should be considered when selecting antibiotic
Side effects
How much resistance the bacteria have built up
Interaction w other drugs
Suggest why antibiotics have no effect on human cells
Human ribosomes are different size 80s whereas bacteria 70s
