F215 module 1 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
o A length of DNA.
o A sequence of nucleotide bases that code for one or more polypeptides.
o There are about 25,000 genes in a human genome.
o Each gene occupies a specific place/locus on the chromosome.
Polypeptides that are coded for by genes:
o Structural proteins-collagen and keratin.
o Haemoglobin.
o Immunoglobulin (Antibodies).
o Cell surface receptors.
o Antigens.
o Actin and myosin in the muscle cells.
o Tubulin proteins in the cytoskeleton.
o Channel proteins.
o Electron carriers.
o Enzymes.
b. Explain the meaning of the genetic code
Genetic code:
o Triplet code-three nucleotide bases code for one amino acid.
o Degenerate code-All amino acids by methionine have more than one code.
o Some codes indicate "stop"/the end of the polypeptide chain.
o Widespread but not universal-in some organisms some codes code for
different things but not all.
c. Describe the way in which a nucleotide sequence codes for the amino acid
sequence in a polypeptide.
1. Hydrogen bonds between the complementary bases on the DNA break.
2. The gene that is being transcribed unwinds and unzips.
3. The activated RNA nucleotides bind with hydrogen bonds complementary
with the exposed bases on the template strand of DNA. This is catalysed
by RNA Polymerase.
4. Two extra phospholipid groups are released to release energy for
bonding adjacent nucleotides.
5. mRNA is produced that is complementary to the template strand of DNA.
6. mRNA is released from the DNA by passing through the nuclear pore to a

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Describe how the sequence of nucleotides within a gene is used to construct a
polypeptide, including the roles of messenger RNA, transfer RNA and ribosomes
Transcription Translation
1. A molecule of mRNA binds to a ribosome. Two codons (six bases) attach to the
small subunit and are exposed to the large subunit. Using energy and an enzyme,
tRNA and the correct anticodon bases form hydrogen bonds with the codon.
2. A second tRNA, with complementary anticodons, bind with the second exposed
codon.…read more

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A peptide bond forms between the two amino acids which is catalysed by an
enzyme present in the small ribosomal subunit.
4. The ribosome moves along the mRNA to read the next codon. A third tRNA
brings another amino acid. A peptide bond forms between it and the other amino
acids. The first tRNA leaves so that it can bring another amino acid.…read more

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The polypeptide chain grows until a stop codon is reached. This is because there
are no corresponding tRNA's.
e. State that mutations cause some changes to the sequence of nucleotides in
DNA molecules
Mutation=a random change to the genetic materials.
Point mutation=Where one base pair replaces another. Also known as
Insertion/deletion mutations=where one or more nucleotide pairs are inserted
or deleted from a length of DNA. Also known as Frameshift mutations.
Different types of substitutions
o Nonsense mutation-leads to the termination of a polypeptide.…read more

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Huntington's disease is caused by a repeating CAG sequence, if the
number goes over a threshold then the protein is changed sufficiently
enough to cause it.
g. State that cyclic AMP activates proteins by altering their three-dimensional
h. Explain genetic control of protein production in a prokaryote using the lac
Structural genes
o Z codes for the enzyme -galactosidase
o Y codes for the enzyme lactose permease.…read more

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The lactose permease enzyme means that it can take up lactose into their
6. -galactosidase can convert lactose to glucose. Glucose can then be used
for respiration.
i. Explain that the genes that animal development of body plans are similar in
plants, animals and fungi in reference to homeobox sequences.
Homeobox genes
o Control the development of an organism including which is the top and
bottom end (polarity) and the position of the organs.…read more

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During development it separates the fingers and toes.
Between the ages of 8 and 14, 20-30 billion cells each year undergo apoptosis.
The role of cells dying should balance the role of cells made by mitosis. If it is
not it can lead to the formation of tumours if there is not enough and if there
are too many cells it can lead to cell loss and degeneration.
5.1.2 Meiosis and Variation
a.…read more

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Prophase I
The homologous chromosomes are pulled apart by the spindle fibres
to opposite poles.
The chismata separate and the lengths of chromatid that have been
crossed over stay attached to the newly attached chromatid.
Telophase I
In animal cells, two new nuclear envelopes form around each set of
chromosomes at the poles. Cytokinesis takes place to divide the cell.
The chromosomes uncoil.
In plant cells, the cell goes from anaphase I to meiosis II
Meiosis II
Prophase II
Nuclear envelope is broken down.…read more

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Chromatids randomly segregate.
Telophase II
Nuclear envelope reforms.
In animals, the two cells divide into four haploid
In plants, a tetrad of four haploid cells is formed.
b. Explain the terms allele, locus, phenotype, genotype,
dominant, codominant and recessive.
Allele-An alternative version of a gene
Locus-Specific position on a chromosome which is occupied by a particular gene.
Phenotype-The characteristics that are expressed in the organism and that can
be observed. It is determined by the genotype and the environment around it
during the development.…read more

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Random fertilisation
o Randomly combines two sets of chromosomes from two individuals.
Random mutation during DNA replication in Interphase.
e. Use genetic diagrams to solve problems involving sex linkage and codominance
Sex linkage
o Haemophilia is carried on the X chromosome
o Parental phenotypes: Carrier mother x Normal father
o Parental genotypes: x
o Offspring phenotypes:Normal female, carrier female, Normal male,
Haemophilic male.…read more


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