Cellular Control Flashcards
Define mutation
A change in the sequence of bases in DNA
What is a point mutation?
A change in a single nucleotide base
What is a frameshift mutation?
The addition or deletion of a nucleotide moves/shifts the reading frame of the sequences of bases, altering every successive codon from the point of mutation
What are the 5 types of point mutation?
- Substitution
- Deletion
- Insertion
- Duplication
- Inversion
What is a silent mutation?
A mutation which results in the same protein being produced
Why can silent mutations occur?
The genetic code is degenerate, so the mutated codon may still code for the correct amino acid
What is a missense mutation?
When one or more amino acids are added to the primary structure of the protein
What effect can a missense mutation have on the phenotype of an organism?
The effect can be neutral, beneficial, or harmful
What is a nonsense mutation?
The result of frameshift mutations, a shorter unfinished protein is often produced
What kind of effect does a nonsense mutation have on phenotype?
A harmful effect
What is a chromosomal mutation?
A mutation leading to the addition or deletion of a portion of a chromosome
Why can a change in the sequence of nucleotides affect the function of a protein?
- 3 nucleotides code for an amino acid
- Change in nucleotides can change the amino acid coded for
- Different amino acids have different R groups
- Different R groups alter 3D shape of protein
- Different shape may affect the protein’s function
How can mutations have a beneficial effect?
A mutation causes a protein with a useful effect to be produced
How can mutations have a harmful effect?
The proteins coded for are no longer synthesised or non-functional proteins are synthesised
What are the 3 types of mutagens?
- Physical
- Chemical
- Biological
What is a mutagen?
Something which induces mutations in DNA
Give an example of a physical mutagen
Ionising radiation
Give an example of a biological mutagen
Some viruses
Give an example of a chemical mutagen
Deaminating agents
What are the 4 types of chromosomal mutation?
- Deletion
- Duplication
- Translocation
- Inversion
What happens in a translocation chromosomal mutation?
A section of one chromosome breaks off and joins another non-homologous chromosome
Give 2 examples of the harmful effects of point mutations
- Sickle cell anaemia
- Cystic Fibrosis
What is gene expression?
The process by which instructions in DNA are converted into a functional product
What is chromatin remodelling?
The control of whether or not a gene is contained within heterochromatin or euchromatin
What is heterochromatin?
The form of chromatin in which DNA is tightly wound around histones
What is the effect of heterochromatin on transcription?
RNA polymerase cannot reach the genes so transcription does not occur
What are the 3 types of transcriptional control in eukaryotes?
- Chromatin remodelling
- Histone modification
- Transcription factors
What transciptional control occurs in prokaryotes?
Operons
What is Euchromatin?
The form of chromatin in which DNA is loosely wound around histones
What is the effect of euchromatin on transcription?
The gene can be accessed by RNA polymerase so transcription can occur
What is the effect of methylation on transcription?
Causes the histones to become more hydrophobic so they bind together more tightly. This prevents transcription by preventing RNA polymerase binding
What is histone modification?
The alteration of histones by the addition of a methyl or acetyl group
What is the effect of acetylation on transcription?
Causes the histone proteins to become more negatively charged so DNA is bound less tightly. This allows transcription as it allows RNA polymerase to bind
What is epigenetics?
The study of changes in organisms caused by modification of gene expression rather then alteration of the genetic code
What is an operon?
A group of genes under the control of the same regulatory mechanism which are expressed at the same time
What are structural genes?
Genes which code for proteins not involved in DNA regulation (e.g. enzymes)
What does the lac Z gene code for?
ß galactosidase
What does the lac y gene code for?
Lactose permease
What is the effect of lactose permease?
Allows the bacteria to take up lactose
What is the function of ß galactosidase?
Enables the bacteria to hydrolyse lactose into glucose and galactose
Why do bacteria not produce enzymes for lactose metabolism all the time?
This would require energy, so it would be a waste
What type of protein does a regulatory gene code for?
Repressor protein
Describe what occurs in a bacterial cell when lactose is not present
- Regulatory gene codes for repressor protein
- Repressor protein binds to the operator, which prevents RNA polymerase from binding to the promoter region
- RNA polymerase cannot bind so the lac genes are not transcribed
Describe how the presence of lactose affect the lac operon
- Lactose binds to the repressor protein and causes a confirmational change in shape of the repressor
- This prevents the repressor from binding
- RNA polymerase can now bind to the operator so the lac genes are transcribed
What is an exon?
A section of DNA or RNA which codes for a protein
What is an intron?
A section of non-coding DNA or RNA
What is RNA processing?
The process by which introns are removed from pre-mRNA
What are transcription factors?
Proteins or short ncRNA which regulate whether RNA polymerase can bind to DNA
What are the two types of trancription factors?
Repressors or activators
How can transcription factors act as activators?
- Transcription factor binds to a specificbinding site on DNA
- The binding of the transcription factor encourages the binding of RNA polymerase
- RNA polymerase binds to the gene so the gene is transcribed
What are the 3 types of post-transcriptional control?
- RNA processing
- RNA editing
- Small interfering RNA
What occurs in RNA processing?
- Entire DNA sequence is transcribed, a cap is added to the 5’ end and a poly A tail is added to the 3’ end
- Introns are removed by splicing resulting in functional RNA which can now be transcribed
What is RNA editing?
A codon within a gene is changed on mRNA, consequently different proteins can be synthesized from the same gene
What is small interfering RNA?
Short pieces of double stranded RNA which cut up mRNA before it can be translated
What are the 2 types of translational control?
- mRNA degradation
- Activation and binding of inhibition factors
What is the role of inhibition factors in translational control?
Proteins which bind to mRNA and prevents it from attaching to ribosomes
What are the 4 types of post translational control?
- Addition of non-protein groups
- Modification of amino acids
- Folding/shortening of protein
- Modification by cAMP
Define body plan
A set of morphological features common to many animals
What is morphogenesis?
The development of form and structure in an organism during its growth from embryo to adult
What are homeotic genes?
Regulatory genes that determine where anatomical structures (e.g arms and legs) will develop in an organism during morphogenesis
What is a homeobox?
A section of homeotic genes
How many base pairs long is a homeobox?
180
What are homeobox genes?
Genes responsible for the development of body plans
What is a homeodomain?
A conserved motif of 60 amino acids found in all homeobox proteins
Why are homeobox genes highly conserved between plants, animals, and fungi?
- It is very important in the development of an organism
- Any changes would result in an organism unlikely to survive
What are HOX genes?
A distinct family of homeobox genes responsible for the correct positioning of body parts
Which kingdom are HOX genes present in?
Animalia
Which organism is often used to study development?
Drosphila (fruit fly)
Why are drosphila a suitable organism for studying development?
- small genome
- cheap
- easy to breed and keep
- short life cycle
Why are drosphila a good model for development in humans?
- similar/shared genes
- similar cells and metabolism
- shared ancestry
What is apoptosis?
Programmed cell death, following a well-defined sequence of events ‘built-in’ to the cell
Outline the steps in apoptosis
- cells shrink in size
- nucleus condenses
- Organelles break down and become enclosed in blebs (extensions of cell membrane)
- blebs are engulfed by phagocytes
What are the roles of apoptosis in growth and development?
- shapes body parts by removing unwanted cells e.g. hands
- formation of synapses
- menstruation (apotosis removes cells which hold the lining of the womb in place)
- metamorphsis e.g. tadpoles to frogs
