Transcript DNA powerpoint

DNA
Discovery
• The scientists Watson and Crick
figured out the structure of DNA in
1953.
Structure
• DNA is in the shape of a twisted
ladder or a spiral staircase.
• We call it the double helix
Sides
• The sides of the “ladder” are
composed of a sugar (deoxyribose)
and a phosphate molecule
Rungs
• The “rungs” of the ladder contain
the nitrogen bases • Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)
Pairing of the Bases
• Adenine always pairs with Thymine
• Guanine always pairs with Cytosine
• A-T
• G-C
Replication
• When DNA replicates (or makes an exact
copy of itself) it must go through a few
steps:
• 1. The two sides unwind and “unzip”
• 2. The nitrogen bases (remember A, T, G,
& C) that are floating in the nucleus will
“hook up” with the now one sided DNA
strand.
• 3. The new copy will be an exact copy of
the original!!!!
Replication
Order of the Bases
• The order of the bases form a code that
specifies what type of protein will be
made.
• For example CGT always means make a
Alanine amino acid. The other pairings of
three letters code for other amino acids.
• Amino acids hook together like beads on a
necklace to make a protein (the protein is
the completed necklace).
Amino Acid Codes
DNA
• DNA is in the nucleus right?
• Well remember how ribosomes make
proteins? And they are floating in the
cytoplasm?
• How does the DNA
message get to the ribosome
when DNA is too big
• to fit out of the nucleus????
• A MESSENGER!!!!
Messenger RNA
• RNA is a lot like DNA, but it has only
one strand instead of two, so it is
“skinnier” and can fit out of the
nucleus.
• RNA has the same nitrogen bases as
DNA except it does not have
Thymine, it has URACIL instead. So
A pairs with U in DNA.
Instead of
Thymine!!!
Types of RNA
• Messenger RNA (mRNA) - takes the
message about what type of protein
to make out of the nucleus to the
ribosome.
• Transfer RNA (tRNA) takes the
amino acids (small parts that make
up proteins) to the ribosome and
adds them to the growing protein.
Protein Synthesis
(Making Proteins)
• DNA unzips and an RNA strand pairs
up with the DNA strand (G pairs
with C, but remember A pairs with
U b/c there is no T in RNA)
• The mRNA then leaves the nucleus
and attaches itself to a ribosome and
passes on the message
Protein Synthesis
(Cont’d)
• The tRNA attaches to mRNA and
hooks up the amino acids in the right
order. Then it goes back out to pick
up some more (like a taxi cab picking
up more people to bring to the
location)
• The amino acids get strung along
into a “necklace” and when it is
complete you have a protein
Mutations
• Sometimes mistakes happen during
the process of protein synthesis.
• The mistake is called a mutation.
• This may cause an incorrect protein
to be made which will cause a
different trait than intended in the
organism.
Mutations
• Sometimes they do not
affect the organism either way.
• Sometimes they can be helpful – like
resistance to an antibiotic if you
were a bacteria.
• Sometimes they can be harmful, like
if a rabbit were born as an albino and
lived in the forest.