Genetics- Cellular Control Flashcards
What is a gene?
A short section of DNA that codes for a polypeptide
What is a mutation?
An error in a gene caused by a change in base sequence of DNA of an organism
What are the features of mutations?
Are sudden, significant and random
What do mutations cause?
An unpredictable form of variation
Why might a mutation NOT be significant?
- Genes are only a small part of DNA
- DNA is degenerate, so a polypeptide can be coded for more than one gene
Why do mutations cause changes in phenotype?
Mutation creates a change in primary sequence (base of amino acids). This causes different bonds to break and be made, changing the specific tertiary shape of proteins. This can cause genes to stop working.
What is a somatic mutation?
A mutation in non-reproductive cells that cannot be inherited
What is a germ-line mutation?
A mutation in an organism’s gamete which can be inherited by offspring
What is the process of antibiotic resistance?
- There is a spontaneous mutation in a growing population in a bacterial population
- The population is exposed to antibiotics
- The resistant bacteria survives and reproduces to generate a population of antibiotic resistant bacteria
What are the causes of mutations?
-Natural and spontaneous during meiosis (multicellular) and mitosis (unicellular)
-Transcription mistake
-Produced by mutagens, such as:
Viruses, Chemicals and Radiation
How can chemicals cause mutations?
Some chemicals are deaminating agents, which can turn cytosine into uracil, changing the base sequence. Also have alkylating agents that add methyl or ethyl groups, resulting in incorrect base pairing during replication
How do viruses cause mutations?
Viruses insert their own genetic material (RNA,DNA) into the host cell, overriding DNA replication
How does radiation cause mutations?
Effects depend on the wavelength and dose of radiation received. Ionising radiation like X-Ray can break one or both DNA strands
What are the different types of transcriptional errors?
- Insertion (Addition) or Deletion of a nucleotide
- Substitution of a nucleotide
- Inversion of two nucleotides
- Insertion creates a frameshift
Transcriptional error example
AGT CCC AAA CCA original AGT ACC CAA ACC A insertion AGC CCA AAC CA deletion AGT TCC AAA CCA substitution AGC TCC AAA CCA inversion
What causes sickle cell anaemia?
A base substitution, where A has been replaced by T. So CAT is replaced by CTT. This means that during translation, the mRNA causes valine to be added to the polypeptide instead of glutamate. There haemoglobin S is formed which is much less soluble and hence forms sticky fibres which distort the erythrocyte
What are the types of chromosome mutation?
- Deletion, where bits of chromosome break off and are lost
- Duplication (section of chromosome gets copied)
- Translocation, where a section of DNA breaks off and joins another non-homologous chromosome
- Inversion, where a section of chromosome breaks off, is reversed and then joins back onto the chromosome
What is Downes Syndrome?
A genetic disorder caused by an extra chromosome 21.
What causes Downes Syndrome?
Caused by non-disjunction, which means there is an uneven distribution of parental chromosomes at meiosis. This leads to a trisomic cell with 3 chromosomes 21, instead of 2.
What are the characteristics of Downes Syndrome?
- Broad forehead
- Short neck
- Fold in eyelid
- Spots in iris
- Short nose
- Protruding tongue
How can genes be regulated?
- Transcriptionally
- Post transcriptionally
- Translationally
- Post translationally
How can genes be regulated transcriptionally?
Genes turned on or off e.g Lac Operon
How can genes be regulated post-transcriptionally?
mRNA stopped from reaching ribosomes so no translation
How can genes by regulated translationally?
Translation stopped and started at ribosomes
How can genes be regulated post-translationally?
Proteins can be modified after translation to change the 3D shape
What mechanisms affect transcriptional control?
- Chromatin remodeling
- Histone modification
What is chromatin remodeling?
Heterochromatin is tightly wound DNA visible during cell division, whereas euchromatin is loosely wound DNA during interphase. Transcription of DNA not possible when DNA is tightly wound because DNA polymerase cannot access the genes. Whereas the genes in euchromatin can be easily transcribed. Protein synthesis only occurs during interphase therefore the presence of euchromatin only during this time is a form of regulation.
What is histone modification?
DNA coils around histones. Histones can be modified to increase or decrease the degree of packing. Acetylation and phosphorylation reduces the positive charge on histones, causing DNA to coil less tightly, allowing certain genes to be transcribed. Methylation of makes the histones makes the histones more hydrophobic so they bind more tightly to each other, causing DNA to coil tighter. This prevents the transcription of certain genes.
What is an operon?
A group of genes that are transcribed at the same time
What do operons control?
Important biochemical processes
What is the Lac Operon?
A collection of three genes that specify proteins that help the bacterial cells utilize lactose.
What do the genes in the Lac Operon control?
LacZ: encodes for an enzyme that splits lactose into monosaccharides
LacY: encodes a membrane-embedded transporter that helps bring lactose into the cell
What does the Lac Operon contain?
- CAP site
- Promoter
- Operator
- Three genes
What happens when there is no lactose?
The lac repressor is bound to the operator so no transcription occurs as this save resources as the enzymes for hydrolysis are not needed
What happens where there is lactose and glucose?
- Allolactose binds to lac repressor
- Lac repressor cannot bind to operator
- Transcription occurs
- Low cAMP means CAP cannot bind to CAP site
- However CAP isn’t needed due to lower demand for transcription as there is a ready supply of glucose
What happens when there is lactose and no glucose?
- Allolactose binds to lac repressor
- Lac repressor cannot bind to operator
- Transcription occurs
- CAP binds to CAP site as cAMP is present
- Promotes further transcription as there is an urgent need for glucose (increase rate of hydrolysis)
What is morphogenesis?
Shaping of an organisms by embryological processes of differentiation of cells, tissues and organs and the development of organ systems
Why are fruit flies often studied in genetics?
- Fast reproduction rate
- Little ethical issues
- Small, easily contained
What is a homeobox?
DNA sequence around 180 base pairs long found within genes that are involved in the regulation of patterns of anatomical development
What are Hox Genes?
Group of related genes that control the body plan of an embryo along the head-tail axis. They determine the type of segment structures will form on a given segment
Why do common patterns of genetic control exist?
Because all the genes have descended from the genes of common ancestors
How do Hox Genes work?
The protein product of each Hox Gene is a Hox protein which is a transcriptional factor. They are capable of binding to specific nucleotides sequences on the DNA called enhancers where they either activate or repress genes.
What is epigenetics?
Control of gene expression by the modification of DNA
What is post-transcriptional control?
Pre-mRNA needs to be converted to mature mRNA before translation can occur. A cap (modified nucleotide) is added to 5’ end and a tail (long chain of adenine) is added to 3’ end. Splicing also occurs.
What is RNA splicing?
In order to become mature mRNA, RNA is spliced at specific points. The introns (non-coding DNA) are removed and the exons (coding DNA) are joined together.
What is post-translational control?
Proteins can be modified after synthesis which changes their functions
Why is apoptosis important in shaping organisms?
It removes unwanted cells and tissues in order to sculpt certain features. For example, the removal of skin between our fingers so they are no longer webbed. Also, cells undergoing apoptosis can release chemical signals which stimulate mitosis and cell proliferation, leading to the remodelling of tissues
Why is mitosis important in shaping organisms?
Increases the number of cells, leading to growth of limbs and other features
How is mitosis and apoptosis regulated?
Hox genes
What factors can affect the expression of regulatory genes?
Can be influenced by internal and external factors. Stress, when the homesostatic balance is upset, can have an impact on the growth and development of an organism. As well as, internal factors like hormones. Drugs can also affect the activity of regulatory genes
