Lesson #9 (10?) Problem set
AGRO 315 Genetics
Questions Due Monday, March 8, 2012, 11:59
Questions from the lecture:
2. Based on classical cytogenetic staining, geneticists could determine that…
___ genes are made of protein
___ chromosomes contain DNA
___ genes are made of DNA
___ chromosomes contain protein
3. 20 amino acids are used to make proteins, 4 nucleotides are used to make
DNA. Based on this biochemistry fact….
_____DNA should be more complex than proteins in their structure.
_____Proteins should be more complex than DNA in their structure.
_____DNA is most likely to be the genetic material
_____Protein is most likely to be the genetic material
4. Based on the Griffith Experiment, which of the following conclusions is (are)
valid?
___The genetic material is stable once it leaves the cell
and can retain information storing functions.
___The genetic material is unstable once it leaves the cell
and loses it’s information storing function.
___The genetic material is alive.
___ DNA is the genetic material
5. Based on the Avery MacLeod and McCarty Experiment, which of the following
are valid conclusions?
___The genetic material is protein combined with DNA
___The genetic material is protein alone.
___The genetic material is DNA alone.
___ In vitro experiments are better for answering molecular level questions than
in vivo experiments
6. Going from knowing that the chromosomes were made of protein and DNA to
knowing that the DNA part of the chromosome was the genetic material took…
___ 2 years
___ 10 years
____ over 20 years
7. Why was determination of the structure of DNA the hot topic in biology in the
1950’s?
___ structure determines function, knowing DNA structure could reveal how it
works.
___ Bill Gates was offering prize money to the first scientists to figure this out.
___ knowing the structure was something companies could patent.
8. Match the discovery with it’s importance.
a. An American biochemist named Chargaff rips DNA out of many kinds of
living things, counts the A,T,G and C nucleotides and always gets about
the same number of A’s as T’s and G’s as C’s. This biochemist later kicks
Watson out of his office because Watson could not draw the structure of a
nitrogenous base.
b. A dedicated European scientist named Rosalind Franklin crystallizes DNA,
shoots X-rays at the crystals and examines the pattern of diffraction.
c. Pauling of Cal Tech fame, shows that biochemists can make discoveries
with legos, tinker toys or other model building kits as long as they have a
sharp mind and right chemical information about their molecule.
d. Two scientists, one a chemist the other a biologist, who were not even
hired to work on DNA structure have a knack for using the data and
strategies of other scientists, the chemical knowledge to do proper model
building and a capacity to keep the big biology picture in mind. Putting all
this together, along with time spent at the Pub, has a history making
result.
____ DNA is made of two chains and has a constant thickness
____ DNA structure makes ‘sense’ when a team considers both the chemistry and the biology
(the structure and the function) and has access to good data, time and motivation.
____ DNA has a symmetry and repetition, perfect for model building
____ ‘A’ nucleotides are opposite ‘T’ nucleotides and ‘G’ opposite ‘C’ in a double stranded DNA
molecule
9. Watson and Crick placed A nucleotides opposite T and C opposite G in their
structure, always a bigger nucleotide opposite a smaller. This placement was in
agreement with the data from which scientist(s) check the correct
___ Franklin
___Chargaff
___ both, meets A=T, G=C and constant thickness fact.
10. Gel electrophoresis: Answer this based on the electrophoresis stations and
animation in the lesson “Electrophoresis, how scientists look at DNA.”
A. Name two things that could be changed in the electrophoresis process so the
DNA fragments run faster?
B. Which chemical binds to the DNA so it is visible on a transilluminator?
___ tracking dye
___ ethidium bromide
C. A band you see in the gel is actually…
a) one piece of DNA
b) many pieces that are all the same length
D. Circle the band in lane 3 (image above) which contains the longest DNA.
E. An electrophoresis gel is mostly….
____agarose particles
___salts
____ water
___air
11.a. Label the four nucleotide pairs on the end of the DNA molecule above with
an A,T,C or G. Use the chemistry details in the picture above as your guide.
b. Assume that a geneticist grows a strain of bacteria in a nutrient rich culture. In
this environment, the bacteria replicates it’s double stranded DNA in 20 minutes.
They transfer the bacteria into a growth media that has a heavy isotope of N15,
instead of normal N14 .
They allow the bacteria to live in the growth media with the heavy N for about 20
minutes. They then extract the DNA out of the cells of these bacteria and weigh
the double stranded DNA. All the doubled stranded DNA molecules extracted
from these bacteria have a weight that is in between the weights of bacteria
growing in N15, or N14 .
Explain this result.
c. If the geneticist left the bacteria in heavy N for 40 minutes, then extracted
double stranded DNA molecules and weighed them they would find…
___ all the doubled stranded DNA would be heavy.
___ all the doubled stranded DNA would be medium weight
___1/2 the DNA would be medium, ½ would be heavy
___1/2 the DNA would be medium, ¼ would be light, ¼ would be heavy