Download Genetics 3 - MaxSkyFan

Of what are chromosomes
composed?
• Proteins (balls) and
nucleic acids (long
double-stranded strings)
• Nucleic acids of
chromosomes are called
DNA (deoxyribonucleic
acids)
• DNA is spooled around
proteins called histones ,
giving us chromosomes.
DNA
• Remember that Nucleotides consist of a
nitrogenous base, a pentose sugar
(deoxyribose for DNA and ribose for RNA), and
a phosphate group
• Nitrogenous bases are either purines (two rings)
or pyrimidines (a single ring)
• Purines include guanine and adenine
• Pyrimidines include cytosine, thymine, and
uracil (U is only in RNA)
• How did we figure this out?
Watson & Crick
•
•
•
•
Used X-ray diffraction data they obtained
from Rosalind Franklin.
They also used Chargaff’s rule: amount of
A=T and C=G
Used tinker toys to find a model that worked
with the data
Watson and Crick were awarded the Nobel
Prize in Physiology and Medicine in 1962 for
their work. They shared the honor with
Maurice Wilkins, the coworker of the then
deceased Rosalind Franklin, because the
Nobel Prize is never awarded posthumously.
Real Biologists of Genus : Watson
& Crick
• We salute you Watson & Crick. As a pair
of lonely guys and their tinker toys, you
were able to compile the work of others
and take it one step further. You found the
structure of DNA and you were able to win
the Nobel prize.
Chargaff’s Rule
• Erwin Chargaff noticed that the
percentage of Adenosine (A) always
equaled the percentage of Thymidine (T)
and that the percentage of Guanosine (G)
always equaled the percentage of
Cytidine (C ).
How does DNA code for genes?
• Alphabet with 4 letters
1. A (adenine)
2. T (thymine)
3. C (cytosine)
4. G (guanine)
• A stretch of DNA (gene)
codes for proteins
(enzymes).
• You have 30,000 genes.
Each is a recipe for an
enzyme.
• Proteins are strands of
amino acids (20 types).
• If each letter (A, T, C, G)
represented an amino
acid, for how many amino
acids could we code?
• Four
• But we need to code for
20!
• How about if we used 2
letter words (e.g., AA, AT,
AC, etc.)?
How DNA codes for proteins
• There would be 16
possible
combinations, but we
need to code for 20
different amino acids!
AA
AT
AC
AG
TA
TT
TC
TG
CA GA
CT GT
CC GC
CG GG
• How many
combinations are
there with 3 letter
‘words’?
• 64!
• So that’s how it
works!
• Soon, we’ll practice
translating proteins.
• DNA (deoxyribonucleic acid)
is a double strand of
nucleotide bases wound
around itself like yarn.
• The two strands of DNA are
complementary, as a base in
one strand bonds to the base
across from it.
• There are different four types
of bases: A (adenine), T
(thymine), G (guanine), and C
(cytosine). A always bonds to
T, and G always bonds to C.
• Thus if you know one strand,
you can determine the other
strand.
Let’s try it
C
T
A
A
T
G
T
•
•
•
•
•
•
•
G
A
T
T
A
C
A
Remember:
•Genes are stretches of
DNA that code for an
enzyme.
•Each enzyme helps make
a chemical reaction occur in
your body.
•That’s how genes affect
the way you are!
How genes code for us
• Why are identical twins
basically identical?
• Because they have the
same genes.
• Any differences you
can see between them
are termed
‘environmental’ as
opposed to ‘genetic’.
Why are traits linked?
• Remember that we only have 23 pairs of
chromosomes and thousands of genes.
• It’s a space issue. Each chromosome
codes for thousands of different genes.
• Genetic recombination: the cross-over of
genetic material for one chromosome to its
respective paired chromosome (ex. A
piece of one 21 trades with a piece of
another 21)
DNA never leaves the protection of
the nucleus
• DNA is protected by
the nucleus.
• If it left the nucleus
and got destroyed or
altered, the cell would
be different and every
cell created from this
cell would have the
same defect or
mutation.
• Thus we create
proteins from genes
by first making a copy
of the gene.
• That copy is called
RNA.
• Then the RNA leaves
the nucleus to be
translated into a
protein.
Mutation and Cancer
• Mutation: an alteration of the genetic code
• Tumor: a solid cell mass formed by the
inappropriate proliferation of cells
• Benign tumor: a tumor that remains
confined to one area
• Malignant tumor: a tumor that is able to
send out cells to proliferate somewhere
else in the body
Mutation
• neutral mutation: If just one nucleotide is
copied incorrectly and it makes no
difference to the amino acid chain.
• point mutation: If just one nucleotide is
copied incorrectly and it makes a major
difference to the amino acid chain.
DNA  RNA  protein
Transcription takes
place in the nucleus
nucleus
DNA
RNA
Cell
Transcription: DNA  RNA
Translation: RNA  protein
RNA
ribosome
Translation takes place
at the ribosome.
Roles of RNA:
•
•
•
•
mRNA: messenger RNA is a copy of the DNA to be
translated. The mRNA is transcribed from DNA and
then travels outside the nucleus to the ribosome.
rRNA: ribosomal RNA is the main machinery that
accomplishes translation by reading the mRNA and
getting the appropriate amino acid (the building block
of proteins) from tRNA.
tRNA: transfer RNA is set to grab a particular amino
acid based on its label. The rRNA reads the label and
knows that the appropriate amino acid is attached to
the tRNA. Don’t worry about tRNA for the exam.
RNA does serve as the genetic storage in some
viruses that do not have DNA.
Transcription: DNA  RNA
• Transcription takes place
in the nucleus.
• Scribes used to copy
books before the printing
press.
• RNA is like DNA except it
has U (uracil) instead of
T.
• GATTACA (DNA)
• CUAAUGU (RNA)
•
•
Before the gene can be
transcribed, the doublestranded DNA molecule
must be unwound a bit
so the two strands can
be separated. Then the
RNA bases are
matched to the DNA
strand to complete
transcription.
Now let’s try translation,
where we translate from
nucleic acid language to
amino acid language.
RNA translation
• Once an mRNA molecule reaches the
ribosome, it can be translated into a protein.
• The ribosome (constructed of rRNA) grabs the
mRNA and reads the molecule three nucleotide
bases at a time. Each set of three nucleotides is
called a codon.
• Each codon codes for a specific amino acid,
using a table.
• For the exam, you should be able to transcribe
DNA to RNA and then translate the RNA to an
amino acid sequence (i.e., a protein) using a
Table provided.
Translation Code
What is GGATTACCAATG?
The universal code of life
• All organisms use the
same code.
• Thus bacteria can read
our genes and produce
enzymes (proteins) we
need.
• Ex. Insulin.
1. Used to harvested from
corpses or pigs
2. Now we get bacteria to
make it for us.