OCR F215 Cellular Control

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F215 Module 1: Cellular Control and Variation
5.1.1 Cellular Control
(a) state that genes code for polypeptides including enzymes
Gene ­ a length of DNA that codes for one or more
polypeptides , including enzymes.
Polypeptide ­ a polymer consisting of a chain of amino
acids residues joined by peptide bonds .
Protein ­ a large polypeptide ­ usually 100 or more
amino acids. Some proteins consist of one polypeptide
chain and some consist of more than one polypeptide
chain.
Genome ­ the entire DNA sequence of that organism. The
human genome consists of about 3 billion nucleotide base
pairs.
(b) explain the meaning of the term genetic code
Genetic Code ­ the sequence of nucleotide bases on a gene that provides the codes for the construction of a
polypeptide of a protein. The characteristics of the genetic code includes:
Triplet code ­ a sequence of three nucleotide bases codes an amino acid.
Degenerate code ­ all amino acids (except methionine) have more than one code .
Stop codes ­ indicates the end of a polypeptide chain (doesn't correspond to an amino acid).
Widespread but not universal ­ where the same base sequence codes for similar polypeptides in
different organisms, but are not always identical
(c) describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acid
sequence in a polypeptide
Transcription ­ the creation of a singlestranded mRNA copy of the DNA coding strand.
Messenger RNA (mRNA) ­ activated nucleotides that uses complementary base pairing to the template strand
to be arranged identically to the coding strand , other than uracil being present and thymine being absent. They
carry the codons that are used to be make the polypeptide.
1. The gene unwinds and unzips , by the length of
the DNA that makes up the gene dips into the
nucleolus . The hydrogen bonds between the
complementary bases break forming two
strands.
Template strand ­ the strand of DNA that
is used to help make mRNA . RNA
nucleotides use the template strand to
make mRNA through complementary base
pairing between the template strand and
mRNA.
Coding strand ­ the strand of DNA that is
identical to mRNA , other than the base
uracil being present in preference to
thymine .
2. Activated RNA nucleotides bind, using hydrogen bonds , to the exposed bases on the template strand,
through complementary base pairing (U binds with A, C binds with G), catalysed by the enzyme RNA
polymerase .
3. Two extra phosphoryl groups are released, which releases energy for bonding adjacent nucleotides .
4. mRNA is formed and passes out of the nucleus through a pore in the nuclear envelope , to a ribosome .

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F215 Module 1: Cellular Control and Variation
(d) describe, with the aid of diagrams, how the sequence of nucleotides within a gene is used to construct a
polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes
Translation ­ the assembly of polypeptides (proteins) at ribosomes.
Transfer RNA (tRNA) ­ lengths of RNA that fold into hairpin shapes and have three exposed bases at one end
where a particular amino acid can bind.…read more

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F215 Module 1: Cellular Control and Variation
(f) explain how mutations can have beneficial neutral or harmful effects on the way a protein functions
Allele ­ an alternative version of a gene. It is still at the same locus on the chromosome and codes for the same
polypeptide but the alteration to the DNA base sequence may alter the protein's structure.…read more

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F215 Module 1: Cellular Control and Variation
Homeotic selector genes ­ specifies the identity of each segment and direct the development of
individual body segments . These are the master genes in the control networks of regulatory genes . There
are two gene families:
o The complex that regulates development of thorax and abdomen segments.
o The complex that regulates development of head and thorax segments.
Mutations of these genes can change one body part to another.…read more

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