A chemical found in the nucleus
DNA
What was the name of the scientist
who worked with mice, and what did
he discover?
Griffiths (1928):
– he studied pneumonia in mice
- he heated a deadly strain of pneumonia, injected it
into the mice and they lived
- the mice inherited material that transformed them
permanently
-he discovered that bacteria is capable of transferring
genetic information
In 1944, Avery expanded on Griffith’s
idea. What did he discover?
That DNA causes death NOT protein in viruses,
and DNA is the genetic material that is
responsible for being passed from one
generation to the next.
Why were scientists skeptical that DNA
was the root of genetics?
It seemed too simple because it only
had 4 nucleotides (ATCG)
Name the 4 nucleotides that are the
building blocks or monomers of
nucleic acid
Adenine, thymine, cytosine, guanine
– these are the rungs of the DNA
ladder
What does each nucleotide contain?
1 - a ring shaped structure called
deoxyribose
2 – a phosphate group
3 - they all have a single or double
ringed nitrogenous base
What is a virus?
1- it is not living
2- it is not made up of cells
3 - it needs a host to reproduce
4 – it injects DNA into a host cell and “hijacks” a
cell’s function
5 – they cannot survive on their own
Name the scientists who discovered that viruses
have protein coats that make up the outside
shell, and DNA on the inside
Hershey and Chase (1952) by using radioactive
materials to track a virus’ movement
-protein never got into a cell
-DNA was injected by the virus into the nucleus
of a cell and took it over
These viruses only attack bacteria
Bacteriophage
What is the shape of DNA?
Double helix
What are the full names of DNA and
RNA and what is the difference
between them?
Both are polymers:
Deoxyribonucleic Acid – double helix
that contains genetic codes
to make RNA
Ribonucleic Acid – 1/2 ladder that
contains codes to sequence amino
acids to make proteins
(picture on next slide)
Which nucleotides have single rings
(shorter) and which have double rings
(longer)?
guanine and adenine have double rings - longer
thymine + cytosine have single rings - shorter
Who is credited with the discovery of the shape
of DNA and its make up?
Cricks and Watson 1953
(stole Rosalind Franklin’s photo #51)
What is it called when nucleotides are
held together by covalent bonds that
connect the sugar of one nucleotide to
the phosphate group of another
nucleotide
sugar-phosphate backbone – the sides
of the ladder
How long are nucleotide chains?
They can vary from a a few hundred to
an infinite number
Why does adenine only pair with
thymine and cytosine only pair with
guanine?
The pairing is due to size—one long and one
short and their ability to form hydrogen bonds.
How does DNA replicate?
A complex of enzymes called helicase “unzip”
the base pairs - this occurs very quickly and
accurately, and always with the original set of
DNA
During DNA copying the two strands of the helix
separate. Each single strand acts as a “negative”
producing a new complimentary strand. What is
this called?
The Template Mechanism
What enzyme is responsible for the
“re-zipping” of a double helix?
DNA polymerase – it re-zips molecule
and proof reads
What kind of bond holds the base
pairs together?
Hydrogen bond