Genetics Flashcards
What are mutations?
Changes in the base sequences in DNA
Can be harmful, beneficial or have no effect
What are the 3 main types of mutation in terms of changes to the DNA?
Insertion, deletion and substition
What are 3 main types of mutation in terms of effects of the mutation?
Silent, nonsense, missense
What is insertion and deletion and give an example of a disease caused by each
Insertion is the addition of an extra nucleotide into the DNA sequence (Huntington’s disease)
Deletion is the removal of a nucleotide (or more than one) from a DNA base sequence (cystic fibrosis)
What is substitution? name a disease caused by this type of mutation
When one nucleotide is exchanged for another (sickle cell anaemia)
What is frameshift?
When insertion and deletion mutations change many codons along the DNA sequence due to them all shifting one or more places left or right - more harmful than substitution mutations
What is a silent mutation?
A mutation in a non-coding region or that produces a different codon for the same amino acid (due to the degenerate code) that has no effect.
What is a nonsense mutation?
A mutation that changes a codon into a stop codon, leading to a shorter polypeptide, which can be very harmful
What is a missense mutation?
A mutation that introduces at least one new amino acid into a protein’s primary structure, which is usually harmful but potentially beneficial or neutral
What are mutagens?
Factors which increase the rate of mutations. Can be biological (e.g. viruses), chemical or physical (e.g. radiation)
What is gene expression?
When a sequence of codons is transcribed and translated into a polypeptide
How can gene expression be controlled at the transcription stage?
- Altering the structure of chromatin (heterochromatin- no
transcription occurs, euchromatin - transcription can
occur) - Transcription factors (molecules that bind to DNA to
either promote or prevent transcription - Epigenetics - acetylation of histones increases
transcription rates, methylation of DNA prevents
transcription - Operons - genes switched off when repressor binds to
operator region, which blocks a promoter region,
preventing RNA polymerase binding and stopping the
transcription of structural genes - genes are switched on
when the repressor is removed
When does heterochromatin form and how is the DNA wound around the histones?
During cell division - DNA wound tightly around histones - no transcription occurs
When does euchromatin form and how is the DNA wound around the histones?
During interphase - DNA wound loosely around histones - transcription can occur
How can gene expression be controlled at the post transcription stage?
mRNA processing - splicing - introns (non-coding DNA) are removed from mRNA. Different polypeptides can be formed by retaining some introns and rearranging exons
mRNA editing - mRNA can be edited by adding, deleting, or substituting nucleotides
How can gene expression be controlled at the translation stage?
Control of mRNA binding - inhibitory proteins prevent binding of mRNA to ribosomes. Initiation factors promote mRNA binding
How can gene expression be controlled at the post-translation stage?
Polypedtide modification - protein folding, addition of non-protein groups, prosthetic groups and disulfide bridges
What does chromatin consist of?
DNA and histone proteins (around which DNA is wound)
What is removed from mRNA?
Introns
What is the difference between regulatory genes and structural genes?
Regulatory genes code for proteins that control the expression of other genes (e.g. repressor proteins).
Structural genes code for proteins that are not involved in regulation (e.g. enzymes, hormones, membrane proteins)
What binds to and removes the repressor protein in the lac operon?
Lactose
What are the regulatory genes that animals, plants and fungi possess to control their growth and development?
Homeobox genes
What does the development of an organism’s body plan also rely on the balance between?
Apoptosis (programmed cell death) and mitosis
Describe the role of homeobox genes in the development of eukaryotic organisms
Homeobox genes are regulatory genes. Homeobox sequences within these genes are 180 base pairs long and code for polypeptide sequences that are 60 amino acids long (called homeodomains)
Homeodomains bind to DNA and switch genes on or off - they are transcription factors
Hox genes are a subset of homeobox genes that are present only in animals - species possess different numbers of these genes (vertebrates have 4 clusters)
Homeobox genes are expressed in a set order
By regulating which genes are expressed in different parts of an organism, homeobox genes control the development of the organism’s body and ensure structures develop in the correct positions.
e.g. a role of homeobox genes early in development is to determine the tail (posterior) and head (anterior) regions of an organism
Homeobox genes regulate both mitosis and apoptosis
What is apoptosis?
The mechanism the body employs to destroy cells in a controlled fashion.
Describe the steps involved in apoptosis
Cell shrinks, nucleus condenses, enzymes break down cytoskeleton, cell breaks into fragments held in vesicles, macrophages digest cell fragments
What digest cell fragments in apoptosis?
Macrophages
What is apoptosis for?
Destroying damaged cells, pruning excess cells and sculpting structures in developing organisms - vital in development
If a region of tissue or organ remains at the same size, what are occurring at the same rate?
Apoptosis and mitosis
Give 2 examples of apoptosis in an organism’s development
Destruction of harmful immune cells
Destruction of damaged cells
Forming shapes of organs and tissues
Removing excess cells (e.g. between digits)
Why do species differ in the number of homeobox genes they possess?
Species differ in the complexity of their anatomy - number of homeobox genes increases with complexity
