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CELLULAR CONTROL Kirsty Stephen




CELLULAR CONTROL REVISION NOTES
2.1.1 What is a gene?
A gene=length of DNA-so a sequence of nucleotide bases that codes for one or more polypeptides.
It is a unit of heredity. Around 25,000 genes in the human genome, few found in mitochondria,
most in linear chromosomes…

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CELLULAR CONTROL Kirsty Stephen




Transcription-first stage of protein synthesis
Is the creating of a single-stranded mRNA copy of the DNA coding strand. First stage of protein
synthesis, an mRNA molecule is made; one strand of the length of DNA is used as a template. There
are free DNA nucleotides in…

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CELLULAR CONTROL Kirsty Stephen




The sequence of amino acids in a protein is essential because:

Forms the primary structure of a protein
The primary structure determines the tertiary structure-how the protein folds up into its 3D
shape and held into that 3D shape by hydrogen or ionic bonds and hydrophobic…

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CELLULAR CONTROL Kirsty Stephen




In prokaryotes, DNA is not inside the nucleus, translation starts as soon as some mRNA has been
made.




Protein activation
Glycogen in muscle cells can be broken down by enzyme-glycogen phosphorylase and synthesised
by enzyme glycogen synthase. If both were happening at the same time, it…

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CELLULAR CONTROL Kirsty Stephen




This may change the final 3D shape of the protein so it doesn't work properly eg. Active sites in
enzymes may not work-substrates can't bind to them

Many genetic diseases = result of DNA mutations:

Cystic fibrosis-in 70% of cases, the mutation is the deletion of…

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CELLULAR CONTROL Kirsty Stephen




methyl groups to DNA or through action of histone proteins Stem cells are undifferentiated and
become specialised as they undergo epigenetic programming in which certain genes are turned off
by methylation or association with histone proteins. It is also possible to turn genes back on using…

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CELLULAR CONTROL Kirsty Stephen




The regulatory gene is expressed and the prepressor protein is synthesised. Has 2 binding
sites-one that binds to lactose and one that binds to the operator region
The repressor protein binds to the operator region. In doing so it covers part of the
promoter region, where…

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CELLULAR CONTROL Kirsty Stephen




The proteins bind to DNA at the start of developmental genes, activating or repressing
transcription and so altering the production of proteins involved in the development of the
body plan

Retinoic acid & birth defects-retinoic acid = derivative of vitamin A. It activates homeobox genes in…

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CELLULAR CONTROL Kirsty Stephen




Involved in development of body plans-mitosis and differentiation create most of body parts and
apoptosis refines the parts by removing unwanted structures eg.

When hands and feet first develop the fingers and toes are connected-only separated when
cells in connecting tissue are removed by apoptosis
As…

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CELLULAR CONTROL Kirsty Stephen




Asexual and sexual reproduction- in asexual reproduction, all of the offspring are genetically identical
to the parent and each other-genetic variation is only introduced by random mutation. In sexual
reproduction-offspring are genetically different from each other and from the parents. Each parent
produces special reproductive cells,…

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