f215 control,genomes and environment notes

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Control, Genome and Environment
Cellular Control & Variation
Cellular Control
(a) state that genes code for polypeptides, including enzymes;
(b) explain the meaning of the term genetic code;
The sequence of the bases on a gene is a code with instructions for the construction of proteins. It
has a number of characteristics:
It is a triplet code- three bases code of an amino acid
It is a degenerate code- All amino acids bar one have more than one code
Some codes don't code for amino acids but are `stop' codons- they indicate the end of the
polypeptide chain
It is widespread but not universal- Codons generally always code for the same amino acid
in every organism, but this is not always the case.
(c) describe, with the aid of diagrams, the way in which a nucleotide sequence codes for the amino acid
sequence in a polypeptide;
1. Free RNA nucleotides are activated, two extra phosphoryl groups are added to make ATP, GTP,
CTP and UTP.
2. The gene to be transcribed unwinds and unzips. To do this the length of DNA that makes up the
gene dips into the nucleolus & the hydrogen bonds between the nucleotide bases break.
3. Activated RNA nucleotides binds, using Hydrogen Bonds, with their complementary exposed
bases on the template strand. This is catalysed by RNA polymerase
4. The two extra phosphoryl are released, releasing energy for bonding two adjacent nucleotides
The mRNA produced is complementary to the nucleotide base sequence on the template
strand of DNA and therefore is a copy of the base sequence on the coding strand of DNA
5. The mRNA is released from the DNA and passes out of the nucleus through a pore in the
nuclear envelope to a ribosome
(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;
1. A molecule of mRNA binds to a ribosome. Two codons are attached to the small subunit of the
ribosome and exposed to the large subunit. The first exposed mRNA codon is always AUG.
Using ATP energy and an enzyme, a tRNA molecule with the amino acid methionine and the
anticodon UAC forms hydrogen bonds with this codon
2. A seconds tRNA molecule, bearing a different amino acid, binds to the second exposed condon
with its complementary anticodon
3. A peptide bonds forms between the two adjacent amino acids. This is catalysed by an enzyme
in the small ribosomal sub unit
4. The ribosome now moves along the mRNA reading the next codon. A third tRNA brings another
amino acid and a peptide bonds forms between it and the dipeptide. The first tRNA leaves and
is able to collect and bring another of its amino acids.
5. The polypeptide chain grows until a stop codon is reached, for which there are no
corresponding tRNAs and the polypeptide chain is complete
(e) state that mutations cause changes to the sequence of nucleotides in DNA molecules;
(f) explain how mutations can have beneficial, neutral or harmful effects on the way a protein functions;
The mutation changes the sequence of amino acids and therefore the phenotype, but this
gives the organism an advantageous characteristic
E.g. Paler skin in more temperate climates absorbs more vitamin D
It is a mutation in a non-coding region of the DNA
It is a silent mutation- although the base triplet has changed, it still codes for the same
amino acid and so the protein is unchanged.
The mutation changes the sequence of amino acids and therefore the phenotype, and the
resulting characteristic is harmful
E.g. paler skin in a hotter climate burns more easily
(g) state that cyclic AMP activates proteins by altering their three-dimensional structure;
ALM June 10

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Control, Genome and Environment
(h) explain genetic control of protein production in a prokaryote using the lac operon;
E. coli grown in a culture medium with no lactose can be placed in a growth medium with lactose.
At first they cannot metabolise the lactose because they only have tiny amounts of the enzymes
needed to catalyse the reaction. A few minutes after the lactose is added, E.…read more

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Control, Genome and Environment
Meiosis and Variation
(a) describe, with the aid of diagrams and photographs, the behaviour of chromosomes during meiosis, and
the associated behaviour of the nuclear envelope, cell membrane and centrioles. (Names of the main
stages are expected, but not the subdivisions of prophase);
Meiosis I
Prophase I
1. The chromatin condenses and supercoils
2. The chromosomes come together in their homologous pairs to form a bivalent.
Each member of the pair has the same genes at the same loci.…read more

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Control, Genome and Environment
(b) explain the terms
An alternative version of a gene
Specific position on a chromosome, occupied by a specific gene
Observable characteristics of an organism
Alleles present within cells of an individual, for a particular trait/characteristic
Characteristic in which the allele responsible is expressed in the phenotype, even in those
with heterozygous genotypes
A characteristic where both alleles contribute to the phenotype
Characteristic in which the allele responsible is only expressed in the phenotype…read more

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Control, Genome and Environment
(e) use genetic diagrams to solve problems involving sex linkage and codominance;
Sex linkage
e.g. Haemophilia
Parental Phenotypes Carrier Mother Normal Father
H h H
Parental Genotypes X X X Y
H h H
Gametes X X X Y
Male Gametes
Female Gametes X Y
Normal female Normal male
h H h h
Carrier female Haemophilliac male
The gene for haemophilia is carried on the X chromosome.…read more

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Control, Genome and Environment
(h) use the chi-squared ( ) test to test the significance of the difference between observed and expected
results. (The formula for the chi-squared test will be provided);
( - )
O is observed
E is expected
The smaller the value of , the more certain we can be that that difference between observed and
expected data is due to chance and is therefore not a significant difference.
To calculate how significant the value is, a table is used.…read more

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Control, Genome and Environment
(n) explain, with examples, how environmental factors can act as stabilising or evolutionary forces of natural
In unchanging conditions, stabilising selection maintains existing adaptations and so maintains
existing allele frequencies.
In changing conditions, directional selection alters allele frequencies.…read more

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Control, Genome and Environment
(s) describe how artificial selection has been used to produce the modern dairy cow and to produce bread
wheat (Triticum aestivum)
Dairy cow
Each cow's milk yield is measured and recorded
The progeny of bulls is tested to find out which bulls have produced daughters with high
milk yields
Only a few good-quality bulls need to be kept are the semen from one bull can be used to
artificially inseminate many cows
Some elite cows are given hormones so they produce…read more

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Control, Genome and Environment
Biotechnology and Gene Technologies
Cloning in Plants and Animals
(a) outline the differences between reproductive and non-reproductive cloning;
Reproductive cloning is the production of offspring which are genetically identical to either the
mother (nuclear transfer), or the other offspring (splitting embryos)
Non-reproductive cloning is the use of stem cells in order to generate replacement cells, tissues or
organs which may be used to treat particular diseases or conditions of humans
(b) describe the production of natural clones in plants using the…read more

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Control, Genome and Environment
(a) state that biotechnology is the industrial use of living organisms (or parts of living organisms) to produce
food, drugs or other products;
(b) explain why microorganisms are often used in biotechnological processes;
Grow rapidly in favourable conditions, with a generation time of as little as 30 minutes
Often produce proteins or chemicals that are given out into the surrounding medium and can be
Can be genetically engineered to produce specific products
Grow well are relatively low temperatures, much…read more


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