Topic 4 - Genetic Information, Variation + Relationships Flashcards
Describe how DNA is arranged in
prokaryotes
In prokaryotic cells, DNA molecules are short, circular and not associated with proteins.
Describe how DNA is arranged in
eukaryotes
In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones.
Name the organelles (other than the
nucleus) which contain DNA and describe how it is arranged there.
The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein.
What is a chromosome?
DNA molecule and its associated proteins.
What is a gene and what does it code for?
(x2)
A gene is a base sequence of DNA that codes for:
1. The amino acid sequence of a polypeptide.
2. A functional RNA (including ribosomal RNA and tRNAs).
What is a locus?
The position a gene occupies on a particular DNA molecule.
What is a triplet and what does it code for?
A sequence of three DNA bases which codes for a specific amino acid.
What is meant by saying that the genetic code is universal?
The same base triplets code for the
same amino acids in all organisms (with some exceptions).
What is meant by saying that the genetic code is non-overlapping?
Each base is only read once as part of a specific triplet.
What is meant by saying that the genetic code is degenerate?
Differenct base triplets or codons coding for the same amino acid.
What is an exon?
Sequences of DNA bases in a gene code for amino acid sequences.
What is an intron?
Non-coding sequences of DNA bases in a gene (i.e. do not code for amino acid sequences).
What is the genome?
The complete set of genes in a cell.
What is the proteome?
The full range of proteins that a cell is able to produce.
Describe 4 similarities between mRNA
and tRNA
- Both polymers of nucleotides / polynucleotide strands.
- Both nucleotides contain phosphate and ribose.
- Both contain adenine, uracil, cytosine and guanine bases.
- Both contain phosphodiester bonds.
Describe 4 differences between mRNA
and tRNA
- mRNA has a linear shape, tRNA has a clover leaf shape.
- mRNA has no hydrogen bonds, tRNA has hydrogen bonds.
- mRNA is variable in length, tRNA is not variable in length.
- mRNA has no amino acid binding site, tRNA does have an amino acid binding site.
What are the 2 stages in protein synthesis?
Transcription and translation.
Where does transcription occur?
Nucleus.
What does transcription in prokaryotes result in?
Results directly in the production of mRNA from DNA.
What does transcription in eukaryotes result in?
Results in the production of pre-mRNA; this is then spliced to form mRNA.
What occurs in the 1st stage of transcription in eukaryotes?
Hydrogen bonds between DNA bases break.
What occurs in the 2nd stage of transcription in eukaryotes after hydrogen bonds are broken?
One DNA strand acts as a template; free RNA nucleotides align by complementary base pairing. In RNA, uracil base pairs with adenine on DNA OR In RNA, uracil is used in place of thymine.
What occurs in the 3rd stage of transcription in eukaryotes after bases pair up?
RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds.
What occurs in the 4th stage of transcription in eukaryotes after RNA nucleotides join together?
Pre-mRNA is spliced (introns are removed) to form mRNA.
What is the role of RNA polymerase?
Joins adjacent RNA nucleotides with
phosphodiester bonds to form pre-mRNA.
What occurs in the 1st stage of translation in eukaryotes?
THe mRNA attaches to ribosomes.
What occurs in the 2nd stage of translation in eukaryotes after ribsomes attach?
The tRNA anticodons (which bring a specific amino acid) bind to complementary mRNA codon.
What occurs in the 3rd stage of translation in eukaryotes after anticodons bind to codons?
Amino acids join by peptide bonds with the use of
ATP.
What occurs in the 4th stage of translation in eukaryotes after amino acids join together?
The tRNA is released and the ribosome moves along the mRNA to form the polypeptide.
What is a gene mutation?
A change in the DNA
base sequence of chromosomes.
What is a deletion mutation?
The removal of one or more bases.
What is a substitution mutation?
The replacement of one or more bases by one or more different bases.
What is a mutagenic agent and what do
they do?
Mutagenic agents can increase the rate of gene mutation.
Name 5 examples of mutagenic agents
X-rays
Gamma rays
UV light
Benzene
Alpha and beta particles
Why might a substitution not cause a
change in the sequence of encoded
amino acids?
The genetic code is degenerate – more than one base triplet could code for the same amino acid (CGA and CGG both code for alanine so the polypeptide remains unchanged).
What is meant by genetic diversity?
Number of different alleles of genes in a population.
Why is variation present in a population?
Random mutations resulting in new alleles of a gene.
What happens to the reproductive success of an organism with a beneficial allele?
Increases.
What is directional selection – include an example
This occurs when the environment is changing, which selects for those
organisms with alleles for a phenotype towards one extreme of a range (e.g antibiotic resistance in bacteria).
What is stabilising selection – include an example
This occurs when the environment is not changing (stable). Organisms with alleles for characteristics towards
the middle of the range survive to
reproduce and pass on their alleles to the next generation (e.g human birth weights).
What is a species?
Organisms with similar characteristics which can interbreed to produce fertile offspring.
