Genes and variation Flashcards
Define gene
A section of DNA in a chromosome coding for one if more polypeptides
Define locus
The position of a gene on a chromosome
What does the gene code for
Amino acid sequence of a polypeptide
A functional RNA including ribosomal RNA and transfer RNA
How many DNA bases code for an amino acid? Why?
3
- Only 20 amino acids regularly occur in proteins
- Each amino acid must have its own code of bases on the DNA
- If each base coded for a different amino acid only 4 amino acid could be coded
- pairs would make 16
- threes make 64 which satisfies 20
Outline 5 features of the genetic code?
- Two amino acids are coded for by a single codon
- The remaining are coded by 2-6
- degenerate code
- triplet is always read in one direction
- the start of the sequence is always coded by one codon
- three codons are stop codons
- each base is only read once (non-overlapping)
- universal coding in all organisms
Define exon
Coding sequence of bases
Define intron
Non-coding sequences of bases
Code for something else
Outline how DNA is in a prokaryote
Shorter
Circular
Not associated with proteins (histones)
No chromosomes
Outline how DNA is in a eukaryote
Longer Linear Linked to proteins (histones) Form chromosomes Mitochondria and chloroplasts contain prokaryote like DNA
Outline the structure of a chromosome
Dispersed throughout the nucleus until cell division
DNA double helix appears as two threads joined by a single point (chromatids)
DNA molecule DNA with histones Coiled DNA histones complex Coils fold to form loops Loops coil and pack together to form a chromosome
Define allele
Alternative form of a gene
Define cancer
A disease resulting from mutations that lead to uncontrolled cell division
Forms a group of abnormal cells called a tumour
From which cells may break away and form secondary tumours elsewhere
Define chromosome
A thread like structure made up from one long DNA molecule
Define chromatid
One arm of a double stranded chromosome
Define centriole
Tiny bundles of protein that form a network of protein fibres called the spindle
Define centromere
The point at which 2 strands of a chromosome are joined together
Define crossing over
When chromatids twist around each other
and bits of them swap over during meiosis
alleles are exchanged between homologous chromosomes
Define differentiation
The process by which cells become specialised
Define diploid
When a cell contains 2 copies of each chromosome (body cell)
Define haploid
When a cell contains 1 copy of each chromosome (gametes)
Define genotype
The alleles an organism has
Define histone
Protein that DNA is wound around in order to fit into the nucleus
Define homologous pair
A pair of matching chromosomes - same genes but different alleles
Define independent segregation
During meiosis 1 when homologous pairs of chromosomes are arranged randomly in a line
Resulting in a random combination of maternal and paternal chromosomes in daughter cells
Define sister chromatids
2 identical copies of a chromosome joined together in the middle
What are the two types of RNA important in protein synthesis
Messenger RNA (mRNA) Transfer RNA (tRNA)
Define genome
The complete set of genes in a cell including those in the mitochondria and or chloroplasts
Define proteome
The full range of proteins produced by the genome
This is sometimes called the complete proteome
In which chase the term proteome refers to the proteins produced under a certain set of conditions
What does mRNA do
Associated with ribosomes
To act act as a template for protein synthesis
What does tRNA do
Binds to a specific amino acid
Hosts the anticodon
Takes the amino acid to the ribosome for protein synthesis
Compare DNA, mRNA and tRNA.
Outline 4
DNA double, RNA single
DNA larger, mRNA smaller, tRNA smallest
DNA double helix, mRNA single helix, tRNA clover shaped
DNA Deoxyribose, RNA Ribose
DNA Thymine, RNA Uracil
DNA Mostly in nucleus, RNA throughout the cell
DNA is constant quantity, RNA varies
DNA chemically stable, mRNA least, tRNA in middle
Define transcription
The process by which DNA is used to form pre mRNA
Define splicing
The process by which introns are removed from pre mRNA forming mRNA
Define translation
The process by which mRNA is used to form a polypeptide
Outline transcription
1) RNA polymerase binds to the DNA and separates the two strands
2) RNA polymerase binds matching nucleotides to the template strand forming pre-mRNA
3) DNA is rejoined together as the pre-mRNA is made
4) Once the stop codon is recognised RNA polymerase detaches
Outline splicing
1) the pre-mRNA’s introns are looped together
2) the introns are spliced out of the pre-mRNA
3) until only the exons remain
4) mRNA then leaves the nucleus via the nuclear pore
Outline translation
1) tRNA binds to its complementary amino acid
2) tRNA and mRNA are brought to the rRNA (ribosome)
3) Anti-codons on the tRNA are complementary to the codons on the mRNA
4) The ribosome forms a peptide bond between the amino acids
5) this is done two at a time until a polypeptide is formed
Define mutation
A change to the quantity of base sequence of the DNA of any organism
What are the 3 different types of point mutation?
Silent
Nonsense
Missense (conservative/non-conservative)
Define silent mutation
Change in the codon that still codes for the same amino acid, resulting in no change to the phenotype
Define nonsense mutation
A change in the codon that results in a premature stop codon, shortening the polypeptide chain length
Define missense mutation
A change in the codon resulting in the production of a different amino acid
What are the 5 types of mutation? (chromosomal and gene)
Addition Deletion Translocation Inversion Duplication
What are the two types of gene mutation?
Point mutation
Reading Frame Shift
Explain point mutation
A substitution of one base for another base resulting in a different codon
Explain reading frame shift mutation
A deletion or addition of a base to a codon, resulting in the reading frame shifting resulting in a completely different polypeptide chain
Outline the difference between spontaneous and induced mutations
Spontaneous mutations arise during meiosis and do not affect the parents whereas induced mutations arise from mutagens and exposure to hazards in our environment
Name three changes in the environment can induce mutation
Radiation Diet Viruses Smoking Alcohol Chemical exposure
Define proto-oncogene
Codes for a protein that stimulates normal cell growth and divsion
Define tumour suppressor gene
Code for proteins that inhibit uncontrolled cell division
Define oncogenes
Mutated proto-oncogenes that increase proteins that stimulate growth and division and increase activity of each growth stimulating molecule
Define mutated tumour suppressor gene
Mutated tumour suppressor gene that cannot repair damaged DNA, control cell adhesion or inhibit cell division
What are the two types of mutation in chromosomes
Polyploidy (multiple sets of chromosomes)
Non-disjunction (different number of individual chromosomes)
