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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…

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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…

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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…

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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…

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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…

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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…

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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…

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o 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…

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o 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…

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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…


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