Unit 1 Flashcards
(48 cards)
What are the requirements of “genetic material”
- Can replicate
- Controls the expression of traits
- Ability to change/adapt
Do polypeptides or DNA have more potential variation/different combinations?
Polypeptides
What is the nucleotide? What are its 3 components? What bond links them together?
The repeating structural unit of DNA and RNA
Phosphate group, Pentose sugar, nitrogenous base
Phosphodiester bonds
What is Chargaff’s rule?
% adenine = % thymine
% cytosine = % guanine
adenine + guanine (purines) = thymine + cytosine (pyrimidines)
What did Rosalind Franklin discover about the structure of DNA?
X-ray diffraction showed that DNA is helical with more than one strand. 10 base pairs per complete turn.
What direction do DNA strands go in?
A phosphate connects the 5’ carbon of one nucleotide to the 3’ carbon of another
Therefore, strand goes 5’ to 3’
What are some general DNA structural features?
•10 base pairs per complete twist
•the two strands are antiparallel
-one runs in the 5’ to 3’ direction and the other goes 3’ to 5’
•the helix is primarily in right-handed in the B form
How is the double-bonded structure of DNA stabilized?
- Hydrogen bonding between complementary bases (A-T is 2 hydrogen bonds, C-G is 3 hydrogen bonds)
- Base stacking (flattened regions face each other)
What two asymmetrical grooves are on the outside of the helix?
- Major groove
- Minor groove
What different forms of the DNA double helix can form?
•B-DNA, the predominant form found in living cells
•A-DNA and Z-DNA, under certain in vitro conditions
What are some of the features of A-DNA?
•right handed helix
•11 bp per turn
•occurs under conditions of low humidity
•little evidence to suggest it is biologically important
What are some of the features of Z-DNA?
•left handed helix
•12 bp per turn
•may play a role in transcription and chromosome structure
What’s the difference between B-DNA and Z-DNA?
B-DNA
•bases relatively perpendicular to the central axis
Z-DNA
•bases substantially tilted relative to central axis
•sugar phosphate backbone follows zigzag pattern
Can DNA form a triple helix? If so, explain
Yes.
Synthetic DNA oligomers were found to complex to double stranded DNA to form a triplex.
Found to occur in nature during instances of recombination and inactivation of specific genes
Potential tool for therapeutic gene inactivation
Explain the structure of RNA
•RNA strands typically several hundred to thousand nucleotides in length
•Only one of two strands of DNA is used as template in RNA synthesis
Explain RNA secondary structure
•although usually single stranded, RNA molecules can form short double-stranded regions
•secondary structure due to complementary base pairing (A to U, C to G)
•RNA double helices are typically right handed (11-12 base pairs per turn)
What are the 4 RNA secondary structures possible?
- Bulge Loop ||>
- Internal Loop ()
- Multibranched Loop +
- Stem-loop 💡
How do viruses self-assemble?
Viruses with a simple structure can self-assemble when genetic material and capsid proteins spontaneously bind to each other
Explain directed assembly in viruses
Complex viruses undergo a process called directed assembly, requiring proteins not part of the virus itself. These noncapsid proteins help with packaging.
Explain the bacterial nucleoid
Bacterial chromosome is found in the nucleoid, not bounded by membrane so the DNA is direct contact with the cytoplasm
Bacterial chromosomal DNA is usually a circular molecule a few million nucleotides in length
Explain the types of genes found in bacterial chromosomes
- Structural gene sequences (encoding proteins) make up most
- Intergenic regions are non transcribed DNA between adjacent genes
How do loop domains form in bacterial chromosomal DNA?
DNA must be compacted about a 1000-fold in order to fit, causing the formation loop domains
What is additional compaction of bacterial chromosomes called?
DNA supercooling, where loop domains get even more compact
What two main enzymes control supercooling in bacteria
- DNA gyrase (topoisomerase II)
•introduced negative supercoils and relaxes positive supercoils - DNA topoisomerase I
•introduced positive supercoils and relaxes negative supercoils
