Genetic Material / Chromosome Organisation Flashcards
1
Q
Provide a brief history of DNA (prior to 1900s)
A
- Some substance must be responsible for passage of traits from parents to offspring
Substance must: - Be stable enough to store information for long periods
- Able to replicate accurately
- Capable of change to allow evolution (Darwinian concept)
2
Q
Who was Gregor Mendel
A
- Early 1900’s
- Chromosomes were shown to be the carriers of hereditary information
- Protein or nucleic acid
3
Q
What was the Griffith experiment
A
- Frederick Griffith (bacteriologist)
- Prepared a vaccine against pneumonia to protect body against future infections by disease causing agent
- Virulent and non-virulent lead to host dying and surviving respectively
- Heat inactivated and living non-virulent can lead to virulent and death
4
Q
What did Avery and Colleagues achieve
A
- Avery, Macleod and McCarty
- Published results identifying transforming principle
- Similar to Griffith experiment
- Chemically separate components (protein, nucleic acids) and determine which are capable of transforming live S. pneumoniae cells
- Only nucleic acid fraction was capable of transforming bacteria
- DNase treated samples showed no transformants
5
Q
What is the Hershey Chase Experiment
A
- Confirmed DNA as hereditary material
- Involved infection, blending and centrifugation
- Protein vs DNA
- Protein was found outside infected cells
- DNA was found inside infected cells
6
Q
What is genetic material
A
- Chemical Nature: Phosphate group, nitrogenous base and pentose sugar (deoxy / ribose)
- Size: DNA strand is 2 nm
- Shape: Double helix, two polynucleotide chains, anti parallel
- Strandedness: RNA (single) and DNA (double)
- Purines: Double-ring, nine-membered structures, adenine (A) and guanine (G)
- Pyrimidines: One-ring, six-membered structures), cytosine (C), thymine (T) in DNA and uracil (U) RNA
7
Q
What is Chargaff’s rule and pairing of bases
A
- 1949
- Total number or purines = total number of pyrimidines
- (A + G) = (C + T)
- Amount of G = C
- Amount of A = T
- Didn’t understand structure
- Understood basic chemistry / relationship between bases
8
Q
What did Wilkins and Franklin discover
A
- 1952
- Developed high-quality X-ray diffraction photographs of strands of DNA
- Suggested that DNA resembled a tightly coiled helix
- Composed of 2-3 chains of nucleotides
- Helical structure with regularities at 0.34 nm and 3.4 nm along axis of molecule
9
Q
What did Watson and Crick discover
A
- 1953
- Published double helix structure
- Discovery was assisted by Chargaff’s ratios and Franklins x-ray diffraction images of DNA
10
Q
Describe the structure of chromatin / chromosome
A
- Chromatin: DNA wrapped around histone octamers
- Chromosomes: Organisation of cellular DNA during division, contains a DNA molecule made up of many genes, numbered only based on size, histones
- Eukaryotic: Linear, multiple replication origins, telomeres at ends, coding / noncoding sequences
- 22 pairs of autosomes
- 1 pair of sex chromosomes
11
Q
How is DNA packaged inside the nucleus
A
- 2 m of DNA packed into 46 chromosomes, fits inside nucleus (0.006 mm)
- DNA wrapped around histone octamers
- Further packing involves action of histone H1
- Solenoid molecules interact with one another causing chromatin to spiral with 6-8 nucleosomes per turn
- Folded into loops (panels D and E)
- Cell Cycle: Affects packing, most condensed at metaphase, temporal form of regulation, not static
12
Q
What is a genome
A
- The chromosome or set of chromosomes that contains all the DNA of an organism
- Prokaryotes (single circular chromosome)
- Eukaryotes (haploid set of nuclear chromosomes)
13
Q
What are characteristics of a eukaryotic genome
A
- Multiple genomes (nuclear, plastic, mitochondria and chloroplast)
- 97% of DNA does not code for protein or RNA
- Increased size = increased complexity of gene structure
- Transcription and translation take place in different compartments
- Monocistronic transcription units
- Transcription and alternative splicing give rise to additional complexity
14
Q
What are transposon-derived repeats
A
- Constitute ~45% of the human genome
- Involve RNA intermediates (retrotransposons) or DNA intermediates (DNA transposons)
- Transposons: Mobile genetic elements, encode enzymes which insert sequence into sites in genomic DNA
- Contribute to spontaneous mutation, genetic rearrangements, horizontal transfer of genetic material
15
Q
What is the concept of base pairing
A
- Base Pairing: A purine on one strand of DNA is always paired with a pyrimidine on the opposite strand
- Base-Pairing Rule: C binds with G and A binds with T
- Complementary Base Pairs: Sequence of bases on strand determines sequence of N bases on other strand of DNA
