Genetics Flashcards
Describe how genetic material is in eukaryotic cells
Very long molecules of DNA
DNA is linear
DNA is associated with proteins called histones forming chromosomes
Describe how genetic material is prokaryotic cells
Only DNA and is not associated with proteins
DNA is circular
DNA is shorter
Found in multiple organelles (mitochondria + chloroplast)
What is a gene?
It is a section of DNA at a particular site on a DNA molecule and occupies a fixed position (locus) and used to code for a specific polypeptide chain
What does a gene code for?
A gene has a specific base sequence that codes for sequence of amino acids in the polypeptide chain and can code for functional RNA (tRNA / rRNA)
What is a Triplet Code?
A sequence of 3 bases in the DNA codes for a specific amino acid
What are alleles?
Alternative forms of Genes
What is the genetic code?
Sequence of bases in the DNA that determines the sequence of amino acids in the polypeptide chain
Explain the features of the genetic code
It’s a Triplet Code (3 bases of the DNA coding for 1 specific amino acid)
Universal in all organisms (indirect evidence of evolution)
Non overlapping + Degenerate
What is the Genome?
The complete set of genes in a cell
What is the proteome?
The full range of proteins that a cell can produce
Explain the process of Transcription?
Involves producing mRNA from DNA in nucleus
1) DNA unwind as hydrogen bonds broken
2) one strand acts as a template to produce a strand of mRNA
3) RNA nucleotides attracted to exposed DNA bases due to comp. base pair rulings
4) the mRNA leaves nucleus via nuclear pores and enter cytoplasm
5) DNA reformed once required mRNA produced
6) Transcription catalysed by enzyme RNA-Polymerase
Explain the process of Amino Acid Activation?
Takes place in cytoplasm. tRNA has a region called anticodon which is a set of 3 bases complementary to a codon of mRNA. Each tRNA has an amino acid binding site. During the process, each tRNA binds with its specific amino acid and is determined by anticodon and requires energy
Explain the process of Translation
1) mRNA associates with a ribosome
2) first 2 codons (6bases) of mRNA enter ribosome.
3) first one attracts it’s complementary tRNA anticodon with its specific amino acid
4) then the second codon does the same
5) ribosome acts as a framework hold mRNA and tRNA together until peptide bond forms between amino acids
6) peptide bond forms between 2 amino acids using energy released by the breaking of the bond between the first codon and amino acid
7) ribosome continues along mRNA with amino acids to polypeptide chain until it reaches a stop codon and the chain is released
8) Primary structure determined and then folds to its secondary/tertiary
What is a polysome?
When several ribosomes move along the mRNA; structure called polysome
What are introns?
Non coding regions within the gene (interruptions). They are between the exons which are the coding regions
What are multiple repeats
These are the non coding regions between the genes
What is a mutation
This is a change in the amount or structure of the DNA of an organism. Only mutations in gametes can be passed onto next gen.
What is Gene mutation?
A change in the base sequence of the DNA of a gene on a chromosome and occurs spontaneously and at random
What are Mutagenic agents? Name some
Environmental factors that increase the rate of gene mutation.
- High energy radiation (X-rays)
- High energy particles from radioactive substances (uranium)
- Mutagenic Chemicals (tar from cigarettes)
In what stage can mutations occur?
During DNA replication in Interphase
Name the 3 types of Mutation
Substitution - one nucleotide is replaced by another with a different base
Addition - An extra nucleotide is added so an extra base is added to the sequence
Deletion - One nucleotide is removed
Explain the effects of mutations
The mutation will change the sequence of bases in the DNA of the gene which leads to a different sequence bases in the mRNA produced during transcription. This will lead to different amino acids in polypeptide chain. The protein may not fold + coil into correct shape and not function. There’ll be different hydrogen, disulphide and ionic bonds leading to different tertiary structure. It will not have correct shaped active site and will not function efficiently
What is a chromosome non-disjunction?
When chromosomes dont separate properly
What does a chromosome non-disjunction cause?
An uneven number of chromosomes in the gametes and therefore genetic diseases such as down syndrome
Why is DNA universal?
The genetic code is the same in all living organisms
Why is DNA degenerate?
The same amino acid can be coded for by more than one triplet
How does DNA become pre-mRNA?
It is transcribed
How does pre-mRNA become mRNA?
It is spliced
How does mRNA become proteins?
it is translated
What is a DNA triplet?
A sequence of 3 DNA bases that code for a specific amino acid
What are introns?
Non coding regions within a gene that are found in pre-mRNA and do not code for polypeptides
What is splicing?
Removal of introns (non coding sections)
Which organisms do not undergo splicing
Prokaryotes
What is a codon?
A triplet of bases found on mRNA that codes for a specific amino acid
What is an anticodon?
A triplet of bases found of tRNA that is complimentary to the mRNA codon
What is tRNA?
Transfer RNA, a polypeptide folded by H-bonds with an amino acid attached. The amino acid is specific to the anticodon
