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Cellular control
By Daniella Di-Fonzo…read more

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(a) state that genes code for polypeptides, including enzymes;
· (b) explain the meaning of the term genetic code;
· (c) describe, with the aid of diagrams, the way in which a nucleotide sequence codes for
the amino acid sequence in a polypeptide;
· (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;
· (e) state that mutations cause changes to the sequence of nucleotides in DNA
· (f) explain how mutations can have beneficial, neutral or harmful effects on the way a
protein functions;
· (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 operon;
· (i) explain that the genes that control development of body plans are similar in plants,
animals and fungi, with reference to homeobox sequences (HSW1);
· (j) outline how apoptosis (programmed cell death) can act as a mechanism to change
body plans.…read more

Slide 3

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A gene is a length of DNA that codes for a
polypeptide/ an enzyme. They're found on
·The genetic code is a sequence of nucleotide bases
with instructions for the construction of a
polypeptide or a protein. It has several
It is a triplet code (a codon)
It is degenerate code, so each amino acid (except
methionine) have more than one code
Stop codons indicate the end of a polypeptide chain.
It is widespread but not universal…read more

Slide 4

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How a nucleotide sequence codes for the
amino acid sequence in a polypeptide
· DNA molecules are found in the nucleus of the cell but the
ribosomes (which carry out protein synthesis) are found in the
· DNA is to large to move out of the nucleus so is copied into RNA
· RNA leaves the nucleus and joins with a ribosome in the cytoplasm,
where it can be used to synthesise a protein. (translation)…read more

Slide 5

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Messenger RNA (mRNA) Transfer RNA (tRNA)
· Made in the nucleus · Found in the cytoplasm
· Three adjacent bases= a codon · Amino acid binding site at one end,
· Carries the genetic code for DNA sequence of three bases at the
from the nucleus to the cytoplasm , other= anticodon.
where it's used during translation. · Carries amino acids that are used to
make proteins to the ribosomes
during translation…read more

Slide 6

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· During transcription an first stage
mRNA copy ofisprotein
of a gene synthesis
made in the nucleus.
1. RNA polymerase attaches to the DNA double helix at the start of the gene
2. The hydrogen bonds between the DNA stands breaks and the double helix uncoils.
3. One strand is used as a template strand to make an mRNA copy
4. RNA polymerase lines up free nucleotides against the template strand by
complimentary base pairing. (T is replaced by U)
5. Once the nucleotides are paired up, they're joined to form an mRNA molecule
6. RNA polymerase moves along the DNA, separating these strands and assembling
the mRNA strand.
7. Once RNA polymerase has passed, the hydrogen bonds reform along the DNA
and it coils back into a double helix
8. When RNA polymerase reaches a stop codon, it stops making mRNA and detaches
from the DNA.
9. The mRNA leaves the nucleus through a nuclear pore and attaches to a ribosome
in the cytoplasm.…read more

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