Week 9 Application Questions Flashcards
Part A: DNA is the genetic material
1. A newly discovered alien unicellular species (the Blob) has a completely different chemical
makeup than we do. So no DNA, no RNA, no protein. Instead, they have the macromolecules ARG,
NAH and ZZZ.
Starting with a pair of cultures, you perform a series of experiments to determine the genetic material of the Blob. Culture 1 is white, and culture 2 is highlighter yellow.
When you lyse (break down the cells) culture 2 and mix the lysate (broken down cells in liquid) with intact culture 1, culture 1 turns highlighter yellow.
A table that describes the samples and their treatments. Fill in the blanks to identify the macromolecules in each sample, and to identify which macromolecule is required for transformation (and thus is the genetic material!)
Part A: DNA is the genetic material
2. Imagine you’re part of a lab that’s looking at groundwater contamination from an industrial process. The waste from the process has a different isotope ratio in several elements than the surrounding area, allowing detection of molecules produced by organisms affected by the waste.
a. One of the affected elements is nitrogen.
What biological macromolecules would you expect to be affected?
• DNA, RNA (nitrogenousbases), protein (amino…=N).
Part A: DNA is the genetic material
2. Imagine you’re part of a lab that’s looking at groundwater contamination from an industrial process. The waste from the process has a different isotope ratio in several elements than the surrounding area, allowing detection of molecules produced by organisms affected by the waste.
b. Another affected element is phosphorus.
What biological molecules is phosphorus part of?
• DNA, RNA = phosphate groups.
Part A: DNA is the genetic material
2. Imagine you’re part of a lab that’s looking at groundwater contamination from an industrial process. The waste from the process has a different isotope ratio in several elements than the surrounding area, allowing detection of molecules produced by organisms affected by the waste.
c. Some of the phosphorus from the industrial process is radioactive.
What consequences would this have for the organisms that ingest the radioactive phosphorus?
Effect of radioactive P: radioactive DNA but no direct effect on nitrogenous
bases
Mutagenic effects come from radiation, not all isotopes ‘radiate’
• Another radioactive element is carbon, what biological macromolecules would you expect to be affected when an organism ingests 14C?
• All biological macromolecules contain C so all would be labelled, 14C is not useful to differentiate between molecules, e.g. in Hershey and Chase experiment both, proteins and DNA would be labelled: some radioactivity inside the E.coli cell (DNA) and some outside (proteins)
Part A: DNA is the genetic material
2. Imagine you’re part of a lab that’s looking at groundwater contamination from an industrial process. The waste from the process has a different isotope ratio in several elements than the surrounding area, allowing detection of molecules produced by organisms affected by the waste.
d. A lab downstream has been looking into uptake of nutrients from contaminated water.
What element(s) should they examine if they want to look at compounds that are broken down and later incorporated into cellular proteins?
• Sulphur.
Nitrogen, oxygen and carbon are all present in other macromolecules, and amino acids don’t have phosphorus
Part B: Structure of DNA
- Look at all of the pieces of evidence that led to the model of the structure of DNA, and fit them together for yourself. Explain how the model is consistent with each piece of evidence.
a. Chargaff’s rules (all of them)
– All DNA is made of the same 4 bases
– Amount of purines = Amount of pyrimidines – Amount of adenine = Amount of thymine
– Amount of cytosine = Amount of guanine
• Can calculate all the bases if have 1 value of a base.
The structural model of DNA shows a
– double helix,
– fixed width of the double helix and
– antiparallel strand in the helix.
Part B: Structure of DNA
- Look at all of the pieces of evidence that led to the model of the structure of DNA, and fit them together for yourself. Explain how the model is consistent with each piece of evidence.
b. Rosalind Franklin’s X-ray diffraction results
• Double helix: X-ray crystallography, Rosalind Franklin
• Fixed width: from X-ray crystallography, Rosalind Franklin – same as width of double helix with purine and pyrimidine
– Also fits with Chargaff’s rules purines=pyrimidines
– A = T and C = G specifies which pyrimidines go with which purines
• Antiparallel: In order to get hydrogen bonding for A-T and C-G pairing, need the strands to be oriented opposite each other, Erwin Chargaff’s results
• Evidence together= model of Watson and Crick
Part B: Structure of DNA
- Look at all of the pieces of evidence that led to the model of the structure of DNA, and fit them together for yourself. Explain how the model is consistent with each piece of evidence.
c. The structure of nucleotides (and the number of rings in purines vs. pyrimidines)
DNA is a double helix of fixed width
– Fixed width = 1 purine + 1 pyrimidine
– Short name, ‘long’ molecule; long name, ‘short’ molecule
Part B: Structure of DNA
- Given what you know about the DNA double helix, why can’t we have AG or CT pairs?
• Purine: purine, Pyrimidine: pyrimidine pairs would result in different width of helix, base pairing rules described by Chargaff, contradict Rosalind Franklins results
• There could be no hydrogen bonding at the nitrogenous bases: partial charges do not match
Part B: Structure of DNA
- How does DNA fit the requirements for the hereditary molecule? Explain for each of the three requirements:
a. Storage of information
To function over life span and to be passed to next generation.
– Information encoded in nucleotide sequence; triplet code: 1 codon (3 bases) = 1 amino acid
Part B: Structure of DNA
- How does DNA fit the requirements for the hereditary molecule? Explain for each of the three requirements:
b. Capable of replication
So each daughter cell gets the same info in cell division.
– Hydrogen bonding-based base pairing directs specificity of replication.
Part B: Structure of DNA
- How does DNA fit the requirements for the hereditary molecule? Explain for each of the three requirements:
c. Ability to change
Important for evolution, mutations in DNA are passed on as well.
– Many known mechanisms for changes in nucleotide sequence (mutation, e.g. base substitutions)
