Genetics Lecture 1 Flashcards
Describe what occurs when the following bacteria are injected into mice. Living non-virulent Living virulent Heat killed non-virulent Heat killed virulent
Living non-virulent Mice lives, no bacteria recovered Living virulent Mice dies, virulent bacteria recovered Heat killed non-virulent Mice lives, no bacteria recovered Heat killed virulent Mice dies, live virulent bacteria recovered
How can transformation and digestive enzymes be used to prove DNA is genetic material?
Use enzymes to digest DNA, lipids, carbohydrates, and proteins one at a time.
Transformation only stops occurring when DNA is digested.
What is Chargraff’s rule?
A=T and G=C
Name the purines.
Adenine and guanine
Name the pyrimidines.
Thymine, uracil, and cytosine
How many rings do purines and pyrimidines have?
Purine - 2
Pyrimidine - 1
What group is present at C2 of DNA and RNA that differentiates them from each other?
DNA - has deoxy
RNA - has hydroxy
Which direction does the DNA chain grow in?
5’ to 3’ direction.
When a nucleic acid chain is being made, where does the phosphate group bind to?
3’ of the previous ribose, and 5’ of the incoming one.
Why are hydrogen bonds ideal for a double helix?
Easy to break, so not much energy required to open and close them.
Name and describe the 3 forms of DNA, including rotation, thickness, and length.
A – right handed, thicker, shorter than B
B – right handed – normal dna
Z – left handed, elongated and thin
What kinds of nucleic acids can viruses be (4)?
dsDNA
ssDNA
dsRNA
ssRNA
Do viruses have a segmented genome or a single chromosome?
Can be either.
Name the T even bacteriophages, and describe their genome structure.
T2, T4, T6
Has dsDNA, single chromosome, and linear
Whats special about the phage λ, and how does it achieve this? What purpose does it serve?
Genome can change from circular to linear and vice versa.
Has complimentary sticky ends to achieve this.
Becomes circular when infecting a host to avoid attack, as its easier to digest linear DNA.
What kind of DNA do most prokaryotes have?
ss or dsDNA
Circular
Where is the DNA arranged in prokaryotes?
In the nucleoid - a false nucleus.
How many chromosomes do humans have?
23, 46 2n
Name the 5 histone proteins. What do they form? Are they highly conserved?
H1, H2A, H2B, H3, H4. Latter 4 form an octamer. Are highly conserved.
What is a nucleosome?
When supercoiled DNA wraps around a histone octamer.
What is linker DNA?
DNA between nucleosomes.
What protein helps stabilise the supercoil in conjunction with linker DNA? What does it form?
H1 histone binds to the linker DNA, forming a chromatin fibre.
Describe the solenoid model.
Histones are stacked on top of each other and coiled, 6 nucleosomes per turn.
What are non-histone proteins called, and how many loops do they form?
Scaffold proteins, forming 8 loops.
What are the two forms of chromatin, and how do they stain? What kind of DNA are they?
Euchromatin - lightly-stained, non-repetitive transcribed DNA
Heterochromatin - darkstained, repetitive non-transcribed DNA.
Describe facultative heterochromatin.
Can become euchromatin if uncoiled, but does so at a partiuclar lifestage.
How many sequences do centromeres have, and what are they collectively called? How long are they?
3 different sequences, 112-120bp long.
What sequence repeat forms a telomere, and how many repeats per telomere? Are they highly conserved?
100-1000 repeats of TTAGGG
Highly conserved.
How do telomere repeats cap the ends of DNA to prevent exposure?
One strand has more repeats. Will form a loop by binding to one of the repeats at the beginning, forming a D loop, replacing the normal strand there, leaving it hanging. This second loop is the T loop.
Describe the D loop and the T loop.
The D loop is a large loop created when the telomere end binds to a previous repeat.
When it does so, it replaces the complimentary strand there, which is left hanging. This creates a smaller T loop.
