12.4 protein synthesis Flashcards
Differences between eukaryotic DNA and prokaryotic DNA
1.Eukaryotic DNA is linear WHEREAS Prokaryotic DNA is circular
2. Euk DNA is associated with histone proteins WHEREAS Pro DNA is not associated with histone proteins
3. Euk DNA contains introns WHEREAS Pro DNA doesn’t contain introns
Which organelles contain similar DNA found in prokaryotes
chloroplasts and mitochondria
INTRONS ARE…
Non-coding base sequences of DNA found within a gene
What are the 4 types of RNA?
a) Messenger RNA (mRNA) – formed during transcription.
b) Transfer RNA (tRNA) – involved in translation.
c) Ribosomal RNA (rRNA) – consist of a large and a small subunit, site of translation.
d) Interfering RNA (RNAi) – inhibits translation [covered in Year 2
What is MRNA
This is a single stranded polynucleotide chain.
· It is a complementary copy of a single gene, from the TEMPLATE strand of DNA.
· A gene is a sequence of nucleotides that codes for a primary structure of a polypeptide chain.
· mRNA’s length will vary depending upon the number of bases that make up the gene, so it is much shorter than DNA.
· The sequence of bases on the mRNA are complementary to the sequence of bases of the gene it is copying.
· Complementary bases pair rules: Guanine with Cytosine and Adenine with Uracil
Compare DNA and RNA
- DNA is double stranded WHEREAS mRNA is single stranded
2.DNA is longer WHEREAS mRNA is shorter
3.DNA uses Thymine WHEREAS mRNA uses Uracil - DNA uses Deoxyribose WHEREAS mRNA uses ribose
- DNA has introns WHEREAS mRNA has no introns
How many nucleotides does one polynucleotide chain of tRNA?
75 nucleotides
What is the shape of tRNA?
single stranded.
It has a cloverleaf structure held by hydrogen bonds
a region of 3 bases known as an…
ANTICODON
a region of 3 bases known as an…
ANTICODON
anticodon is complementary to…
the codon on the mRNA
Define Genome
complete set of genes in a cell
Define Proteome
full range of proteins that a cell is able to produce.
Define Loci
position of a gene within chromosome
Define Allele
a different version / form of a gene
Define Gene
a DNA base sequence that codes for a sequence of amino acids in a polypeptide
Describe Transcription
- (DNA Helicase) Hydrogen bonds are broken so strands separate;
- Only one DNA strand acts as template;
- RNA nucleotides attracted to exposed bases;
- (Attraction) according to base pairing rule Adenine-Uracil, Cytosine-Guanine:
- RNA polymerase joins (RNA) nucleotides together forming phosphodiester bonds through condensation reactions;
- Pre-mRNA spliced to remove introns (in Eukaryotes)
Describe Translation
- mRNA binds to ribosome;
- Ribosome finds the START codon;
- Idea of two codons/binding sites;
- (Allows) tRNA with complementary anticodons to bind/associate with codon;
- (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules) using energy from ATP; 6. tRNA released as Ribosome moves along (mRNA to the next codon)/translocation described;
- Ribosome releases polypeptide into RER when the STOP codon is reached.
3 Bases on:
DNA-
mRNA-
tRNA-
TRIPLET
CODON
ANTICODON
The types of genetic codes are:
-Universal
-Non-overlapping
-Degenerate
Definition of EXONS
coding sequences within a gene of DNA
Universal definition
the same 3 bases on mRNA (codon) / DNA (triplets) code for the same amino acids in all organisms (The mechanism of transcription and translation are universal throughout all organisms)
Non-overlapping definition
Each base is read once in a triplet
Degenerate definiton
More than one triplet for each amino acid
A mutation causes ____ to the DNA base sequence
change
what is a gene mutation?
a change to a single base in the DNA base sequence of a gene. These mutations occur randomly and happen spontaneously
concequence of gene mutation are…
a change in the PRIMARY STRUCTURE OF POLYPEPTIDES, sequence of amino acids in the polypeptide chain.
May alter the SECONDARY STRUCTURE (change the position of the weak Hydrogen bonds affecting the alpha helices and beta-pleated sheets)
· May alter the TERTIARY STRUCTURE (change the position of the weak Hydrogen, Ionic bonds between the R groups of amino acids and the Disulphide bonds) and may alter the BINDING site or ACTIVE site of enzymes and make the protein non-functional.
when does mutation occur?
During DNA replication
what 3 mutations can occur:
· Substitution
· Deletion
· Addition
what is substitution known as and why
This is known as a silent mutation
the mutation does not change the amino acid coded for, so will have no effect on the polypeptide chain
what describe addition/deletion mutation results in (1 full DNA nucleotide base is Gained or Lost)
an alteration of the base triplets from the mutation onwards. The reading frame has been shifted to the right / left by one base, and so is known as a frame shift.
mutations occur spontaineously (randomly) what can they be?
· Advantageous
· Disadvantageous
· Neutral
what are the mutagenic agents?
- High energy ionising radiation (X rays and gamma rays and alpha and beta particles)
- DNA reactive chemicals
- Biological agents such as some viruses and bacteria.
How does meiosis go wrong via Chromosomal mutations
daughter cells produced contain too many chromosomes
A pair of homologous chromosomes may fail to separate during metaphase 1 or sister chromatids fail to separate in metaphase 2.
This is called chromosome non-disjunction.
what causes down syndrome?
non-disjunction of chromosome 21. When gametes fuse at fertilisation offspring has three copies of chromosome 21, rather than 2.
what causes down syndrome?
non-disjunction of chromosome 21. When gametes fuse at fertilisation offspring has three copies of chromosome 21, rather than 2.
What are Inversion mutations?
when a segment of bases is reversed end to end.
What are Inversion mutations?
when a segment of bases is reversed end to end.
what are Duplication mutations?
A doubling of a part of a chromosome, of an entire chromosome, or even the whole genome
What are Translocation mutations?
When groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes.
An allele is…
a different version of the same gene.
Genetic diversity (Gene pool) is…
the number of different alleles of genes in a population
Any mutation could provide a:
· Selective advantage
· Neutral (does nothing)
· Selective disadvantage
What is natural selection?
Process by which organisms that are better adapted to their environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele within the population.
What are the different natural selection things
· Variation exists within a population (caused by Mutation)
· Better adapted individuals more likely to survive and reproduce (differential reproductive success.
· These organisms are more likely to pass on their alleles.
· Those which are less well adapted fail to survive and reproduce.
· These organisms are less likely to pass on their alleles.
· Organisms are therefore subject to selection pressure due to the environment they live in.
· Selection pressure determines the spread of an allele within the gene pool.
· Selection pressures can be either BIOTIC or ABIOTIC.
What is a normal distribution?
A wide range of variations in phenotypes due to mutations of genes (for example mice has different variation in their phenotype shown by fur colours ranging from light to dark in the population, considering environment mice can camoflague when hiding from predators)
What is a Stabilising selection?
- Selection against both extremes
- Only mean phenotype are passed on to future generations in greater numbers
- frequency of mean alleles coding for mean phenotype increases
- Alleles coding for both extreme phenotypes decrease
What is directional delection?
- selection for only one extreme
- individuals with advantagous allele have increased in reproductive success
- alleles for one extreme are passed on to future generations in greater numbers
- frequency of the extreme allele coding for extreme phenotype increases over time
5.alleles coding for other phenotype decreases within the population
Explain how selection occurs in living organisms
- variation due to mutation
- different environmental/abiotic/biotic conditions / selection pressures
- selection for different/advantagous features/characteristics
- different reproductive success
- leads to change in allelic frequency
- occurs over a long period of time
Describe the serial dilution method
- Take one part of the culture medium (which holds millions of bacteria)
mix with 9 parts of sterile water, you complete a 1/10 dilution. This divides the number of bacteria in the culture medium by 10 - you can continue this process to make a serial dilution
- by taking 1ml of the previous solution and mix it with 9ml of sterile water you can create 1/100
This divides the bacteria in the original culture medium by 100
Using a dilutions which is too low to count the number of bacteria can lead to
- the count being unlikely to be reproducible and accurate
- as there are too many cells so they will be overlapping
Using a dilution which is too high to count the bacterial will lead to…
the original dilution being so diluted that there will be no remaining bacteria to see
