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Topic 6 ­ Infection, immunity and forensics…read more

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Investigating time of death
· Temperature of a body can give some
indication of how long a person has been
· The presence of absence of rigor mortis also
can be used to estimate time of death.
· The stage of succession of organisms on a
corpse combined with information on the
species life cycles in similar conditions and
temperatures can help to estimate time of
death (known as forensic entomology).…read more

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· The process which forms mRNA.
· Double helix is unzipped as hydrogen bonds between
bases are broken by RNA polymerase.
· The prime DNA strand (template strand) is used to
order the sequence of nucleotides in an RNA
transcript. RNA polymerase joins many small
nucleotide units together to form mRNA.
· Every triplet code of DNA gives rise to a
complementary codon on the mRNA. Every thymine is
replaced with uracil.
· mRNA passes through the pores in the nuclear
membrane where they then move to the surface of
the ribosomes.…read more

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· tRNA is found in the cytoplasm, and consists of a unit of three
bases known as the anticodon and an amino acid.
· Ribosomal RNA holds together the mRNA, tRNA and the
enzymes controlling protein synthesis.
· Each mRNA strand has a start codon (AUG) and a stop codon
(UAA, UAC or UGA). The mRNA becomes attached to a
ribosome and the ribosome starts reading it and coding for
the complementary amino acid.
· Then, tRNA lines up its anticodon alongside the
complementary codon in the mRNA. Hydrogen bonds form
between bases, peptide bonds join between the amino acids.
When the end is reached, a completed polypeptide chain is
formed. (Then primary, secondary, tertiary structure...)…read more

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Post-transcriptional changes
· In recent years, it appears to have been shown that the `one
gene, one polypeptide' theory is over simplistic.
· The RNA transcribed from DNA is now called `pre-mRNA' and
contains some nonsense sections that do not code for any
protein, known as introns.
· The areas of the RNA that do code for the polypeptide chains are
known as exons.
· Before the mRNA lines up on ribosomes after transcription, the
ends are capped so that it is not attacked by enzymes, the
introns are removed, and the exons are joined together in a
process called RNA splicing. This is carried out by enzymes
known as spliceosomes.
· These changes lead to more variety in phenotype, as the areas
that are removed can be varied.…read more

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DNA profiling
· Individuals and species can be identified through patterns in
their DNA. Introns are the regions used in DNA profiling.
· There are short sequences of DNA within introns that are
repeated many times. Mini-satellites have 20-50 bases
repeated from 50 to several hundred times. Micro-satellites
have 2-4 bases repeated 5-15 times.
· DNA strands are chopped into fragments using restriction
enzymes (e.g. restriction endonucleases), which cut the DNA
molecule at specific base sequences known as recognition
· The fragments are separated using gel electrophoresis. DNA
fragments are placed in wells in agarose gel medium in a
buffering solution to maintain a constant pH, along with
known DNA fragments.…read more

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this is very helpful, thanks :)




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