Cellular Control OCR A2 Biology

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Biology F215
Cellular Control
Key Words
Allele - An alternative version of a gene
Anticodon - Three unpaired nucleotides in tRNA that bind to a complementary codon on mRNA during translation
Apoptosis - Programmed orderly cell death with an cells die after undergoing the maximum number of divisions
Chromosome mutation - A random change to the number or structure of chromosomes in a cell
Codon - A triplet of three bases on mRNA
Cyclic AMP (cAMP) - A secondary messenger within cells that binds to and alters the activity of specific enzymes
Deletion - The loss of nucleotide pair(s) from a DNA sequence
DNA mutation - A change to the sequence of bases in DNA
Frameshift mutation - A mutation in which the insertion or deletion of nucleotide pairs changes the reading frame for the
Gene - A length of DNA that codes for one (or more) polypeptides/proteins, some genes code for RNA and regulate other
Genetic code - A sequence of three bases in DNA that code for a particular amino acid in a polypeptide chain
Genome - All the genetic information within an organism or cell
Homeobox genes - Genes that control the development of the body plan of an organism
Homeotic selector genes - Direct the development of individual body segments, they act as master genes that control other
regulatory genes
Hox clusters - Groups of homeobox genes
Insertion - The introduction of extra nucleotide pair(s) into a DNA sequence
Missense mutation - DNA mutation that changes the codon for one amino acid to the codon for another amino acid
Morphogen - A substance that controls the pattern of tissue development; it is produced in a particular region of a developing
organism and diffuses to other cells which respond by entering a specific developmental pathway depending on its
Mutation - A structural change to genetic material either to a gene or to a chromosome
Necrosis - Disorderly, often accidental cell death
Nonsense mutation - A DNA mutation that introduces a premature STOP codon, the mRNA produced is then translated to give a
truncated polypeptide
Operon - A transcriptional unit consisting of structural genes that work together under the control of an operator gene such as
lac operon
Point Mutation - Substitution, addition or deletion of a single nucleotide pair in a DNA sequence
Phagocytosis - The endocytosis of large, solid particles into a cell
Polypeptide - A large polymer molecule made of many amino acids joined together by peptide bonds

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Promoter - A DNA sequence at the start of a gene to which RNA polymerase binds to start the process of transcription
Protein - A macromolecule composed of one long polypeptide or several polypeptide chains
Proto-oncogene - The gene that can undergo mutations to become an oncogene, which induces tumour formation - cancer
Silent mutation - The DNA mutation that doesn't produce any alteration in the polypeptide sequence
Segmentation genes - The genes that control the development of polarity - which is head or tail…read more

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How does the nucleotide sequence code for the amino acid sequence in a polypeptide?
Proteins are assembled in the cytoplasm at ribosomes and genes are on chromosomes in the cell nucleus so
how are polypeptides formed?
o Firstly a copy of the genetic code has to be made which is able to pass through a pore in the nuclear
envelope into the cytoplasm
This is done by a process known as transcription with a copy of the gene formed by messenger
o Transcription…read more

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The free tRNA is released and the ribosome moves one codon along the mRNA. Another tRNA with its attached amino acid
binds via complementary base pairing to the next codon that is exposed within the ribosome. A peptide bond then forms
between the growing polypeptide chain and the new amino acid.
The free tRNA is released and the ribosome moves one codon along the mRNA.…read more

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How can a change in structure lead to a change in enzyme activity?
A change in the base sequence may alter the amino acid sequence
o This may alter the tertiary structure
Which may change the shape of the active site
Active site is no longer complementary to the substrate
How does this apply to messengers?
Adrenaline or glucagon bind to their specific cell surface receptors on hepatocytes the enzyme adenyl cyclase is
o Which synthesises cAMP from ATP
Cyclic AMP is a second…read more

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One or more bases are inserted
o Deletion
One or more bases are lost from the sequence
Missense mutation
o Changes the codon for one amino to that of another
Silent mutation
o No change in amino acid sequence
Nonsense mutation
o Introduces a premature STOP codon so the mRNA produced gives a truncated polypeptide
Frameshift mutation
o Amino acid sequence altered after insertion point
What are the effects of mutation?
Base substitution
o Only one amino acid changed
May be a silent mutation
No…read more

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Polypeptides have a specific 3D shape and will only transport one substance or bind one substrate that is
complementary in shape to its active site
How is the production of lactose permease and galactosidase co-ordinated?
o The lacZ and lacY genes are part of the same operon, so they are under the same regulatory control and
are transcribed to produce a single mRNA
What is the advantage to E.…read more

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Lactose binding to the repressor molecules occurs through an allosteric mechanism, by binding the
repressor molecule changes shape so it can no longer bind to the operator region - the repressor now
dissociates from the operator region
With the promoter not being blocked by the repressor, RNA polymerase can bind to it and
initate the transcription of the structural genes Z and Y into the lac enxzymes
galactosidase and lactose permease are synthesised and lactose can be utilised as
a respiratory substrate
o As a…read more

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Polypeptides act as
transcription factors which
bind (via homeodomain) to
specific DNA sequences
located upstream of their
target genes and increase their
Are arranged in hox
clusters along the
Homeotic mutations occur when the
Homeotic selector genes which act as
master control genes that turn on other
genes and initiate a particular pathway
of development, are mutated and one
body part is transformed into another
Fungi, plants and vertebrates
homeobox genes work in similar ways
o When cuttings are taken from
plants the…read more

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It activates homeobox genes in vertebrates in the same order that they are expressed in
developing systems such as the axial skeleton and the CNS
This systems both run head to tail
o However the amount of retinoic acid is crucial
Too much taken in by a pregnant woman during the first month of
gestation particularly will interfere with the normal expression of
these genes
This will cause birth defects including cranial deformities
How is cell death programmed?
Apoptosis is a programmed cell death that…read more


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