What is a mutation?
- An unpredictable change in the genetic material of an organism
Name and describe 3 types of mutation
- Substitution= replacement of one nucleotide for another
- Deletion= the loss of a particular nucleotide
- Insertion= the addition of an extra nucleotide
What would be the effect of 3 mutations?
- Substitution= could be silent and not change the amino acid
- Deletion= causes major change due to frameshift, all subsequent codons will be shifted altering all amino acids downstream
- Insertion= same as deletion
What are mutagens?
Agents which can lead to mutations
What are the 3 types of point mutations?
Silent
Missense (changes protein)
Nonsense (stop codon)
What is the LAC operon?
A group of 3 genes (lacZ, lacY, lacA) involved in the metabolism of lactose. They are structural genes as they code for 3 enzymes (B galactosidase, lactose permease and transacetylase) and are transcribed onto one molecule of mRNA.
WHat are the 3 genes expressed as a part of the lac operon?
Lactose permease= a membrane protein needed to increase uptake of glucose
B galactosidase= enzyme which breaks down lactose int glucose and galactose
Transacetylase= transfers acetyl from acteyl coA to galactoside
How can a mutation be beneficial or damaging?
Damaging= phenotype is affected negatively as proteins are no longer synthesised or proteins synthesised are non functional
Beneficial= new and useful characteristic is presented
Name physical mutagens and how they cause mutations
Ionising radiation= break one or both DNA strands
Name chemical mutagens and how they cause mutations
Deaminating agents= chemically alters bases in DNA, changing the base sequence
Name biological mutagens and how they cause mutations
Alkylating agents= methyl or ethyl groups are attached to bases causing incorrect base pairing
Base analogs= incorporated into DNA in the place of the ususal base during replication, changing base sequence
Viruses= viral DNA insertion changes base sequence
What can changes in chromosome structure include?
Deletion- a section breaks off and is lost within the cell
Duplication- sections get duplicated
Translocation- a section of one chromo breaks off and joins another non homologous chromo
Inversion= a section of a chromo breaks off and is reversed
Name the levels at which genes can operate
Transcriptional (turned on/off)
Post transcriptional (mRNA can be modified, regulating translation)
Translational (can be stopped or started)
Post translational (proteins can be modified after synthesis affecting their functions)
How does chromatin remodelling affect the transcription of genes?
- Heterochromatin is tightly wound DNA causing chromos to be visible during cell division
- Euchromatin is loosely wound DNA present in interphase
- Transcription of genes is not possible when DNA is tightly wound as RNA polymerase cannot access the genes
How is histone modification an example of transcriptional control?
- addition of acteyl groups or phosphate groups reduces positive charge on histones causing DNA to coil less tightly
- allowing certain genes to be transcribed
- adding methyl groups makes histones more hydrophobic so they bind more tightly, causing coiling and preventing transcription
What is meant by epigenetics?
A term that is used to describe the control of gene expression by the modification of DNA.
What is an operon?
- A group of genes that are under the control of the same regulatory mechanism and are expressed at the same time
What does the regulatory gene for the lac operon do?
It codes for a repressor protein which prevents the transcription of the structural genes in the absence of lactose
How is gene expression regulated at the transcriptional level?
Transcription factors (proteins which initiate or inhibit transcription)
How is gene expression regulated at the post transcriptional level?
Splicing, introns are removed to produce mature MRNA for translation
How is development controlled by homeobox genes?
Code for transcription factors that activate genes when they’re needed during zygote development
Acetylation
- addition of acteyl groups
- reduces +ve charge on histones and this causes DNA to coil less tightly
- allows certain genes to be transcribed
Methylation
- Makes histones more hydrophobic
- binds more tightly
- coil is tighter
- prevents transcription
Morphogenesis
The regulation of the pattern of anatomical development
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Biological membranes33
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Communicable diseases65
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Biological molecules54
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Nucleic acids33
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Enzymes32
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Exchange surfaces32
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Cell structure30
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Cell organelles22
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Cell division40
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Transport in animals57
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Transport in plants49
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Classification and evolution51
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Homeostasis69
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Ecosystems31
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