Download Cellular Division

DNA
The BIG show!
All animations are from Virtual CellAnimation Collection
http://vcell.ndsu.edu/animations/home.htm
Watson and Crick
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1953 the structure of
DNA was finally
described
Based on Roselind
Franklin and Maurice
Wilkins’ crystallography
of DNA (Wilkins shared
in Nobel prize 1962 –
Franklin had died)
http://www.odec.ca/projects/2007/knig7d2/images/WatsonCrick.jpg
Double Stranded Helix
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DNA is comprised of
two strands of nucleic
acids - bases
6 carbon sugar –
phosphate backbone
helix – twists around
each other, like the
stripes of a peppermint
stick
http://whyfiles.org/034clone/images/dna_molecule.gif
Structure of DNA
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Primary
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Secondary
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DNA is wrapped around
histones
Tertiary
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Sequence of base pairs
along one strand – ATGC
Histones are grouped into
bundles
Quaternary
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DNA located on pairs of
Chromosomes
http://employees.csbsju.edu/hjakubowski/classes/ch331/DNA/chromosome.gif
Nucleotides
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DNA is made up of subunits which scientists called nucleotides.
Each nucleotide is made up of a sugar, a phosphate and a base.
There are 4 different bases in a DNA molecule:
 adenine (a purine)
 cytosine (a pyrimidine)
 guanine (a purine)
 thymine (a pyrimidine)
The number of purine bases equals the number of pyrimidine
bases
The number of adenine bases equals the number of thymine
bases
The number of guanine bases equals the number of cytosine
bases
The basic structure of the DNA molecule is helical, with the
bases being stacked on top of each other
What does that mean?
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Adenine is hydrogen
bonded to Thymine
Guanine is hydrogen
bonded to Cytosine
DNA is directional from
5’ to 3’
http://porpax.bio.miami.edu/~cmallery/150/gene/c16x6base-pairs.jpg
Directional?
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The DNA is “read” from
the 5’ to the 3’ end, just
like we read words from
left to right
When DNA is
replicated, it is read
from 5’ to 3’
The two strands unzip
to allow room for
replication factors
https://eapbiofield.wikispaces.com/file/view/DNA-replication.jpg
Why is that important
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Double stranded adds
stability to DNA
Easy to find errors in
copying or transcribing
to RNA or mutations
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Easy to find T with a G or
C with an A
http://www.science.mcmaster.ca/mciars/Doug%20Boreham/Website_July2/Images_forwebsite/prymidine_dimer.jpg
Genes
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Areas of DNA have readable sequences
which code for genes
Many parts of the genome are “junk DNA”
Genes can have differences in the AT and
GC, which form alleles
If not detrimental, the mutation will continue
If advantageous, the allele will become more
common
Questions?
BJ Shaw Panochthus frenzelianus American Museum of Natural History 2004
DNA to RNA to Protein
Overview
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How it works
DNA – double stranded
to protect and reduce
the mutations
RNA – unstable, and
breaks down quickly in
the cell
Types of RNA
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mRNA (messenger
RNA) is transcribed
from DNA
tRNA (transfer RNA) is
the molecule that
carries amino acids
rRNA (ribosomal RNA)
reads mRNA and
matches tRNA to build
the protein in the
correct sequence
http://www.aps.anl.gov/Science/Highlights/2001/Images/ribomain.gif
Types of RNA
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cRNA (catalytic RNA)
catalyses many reactions in
the cytoplasm of the cell.
snRNA (small nuclear RNA)
have various roles in the
processing of the other
classes of RNA.
snoRNA (small nucleolar
RNA) over 100 of them
found in the nucleolus
where they are involved in
several functions including
making ribosomes
Amino Acids
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Four nucleotides
(Adenine, Thymine,
Guanine, and Cytosine)
translate into 20
different amino acids
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If 1 nucleotide = 1 amino
acid, only 4 amino acids
If 2 nucleotides = 1
amino acid, then 16
amino acids (still short)
If 3 nucleotides = 1
amino acid, then 64
amino acids (too many)
http://www.ccs.k12.in.us/chsTeachers/BYost/Biology%20Notes/translation_files/image007.jpg
Amino Acids
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Closer look…
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AUG = methionine, the
start of the protein
sequence
UAA = stop
UAG = stop
UGA = stop
Other codes allow for
“wobble” room
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For example, serine
starts with a UC, and
any other nucleotide
http://www.ccs.k12.in.us/chsTeachers/BYost/Biology%20Notes/translation_files/image007.jpg
Protein Synthesis
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DNA unzips
Similar to replication,
DNA is copied
(transcription)
Uracil is the molecule
that pairs with Adenine
rather than Thiamine
http://upload.wikimedia.org/wikipedia/commons/5/5e/RNA_polymerase_%281i6h%29.png
Protein Synthesis
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mRNA is edited
mRNA is spliced
mRNA exits the nucleus
of the cell and is
associate with the small
subunit of rRNA (a
ribosome) for
translation
The protein is
constructed one amino
acid at a time
Proteins
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Complex molecules
One of the four major types
of molecules found within
the cell
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DNA, RNA, and lipids are
the other three
These comprise the
variation found within
populations
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The amount of melanin will
determine the color of the
iris – or it is at least 74%
responsible
http://discovermagazine.com/2007/mar/eye-color-explained/eyes-400.jpg
Questions?
BJ Shaw Megatherium americanum Museo de La Plata 2008