Unit 2: Lecture 2 Flashcards
In a set of 23 pairs of chromosomes, each chromosome has 2 chromatids. How many DNA double helices are there?
92
How many chromatids does a chromosome have?
each chromosome has 2 chromatids before the cell divides
How many pairs of homologous chromosomes do we have?
23
Where does each chromosome in a pair of chromosomes come from?
one chromosome from mother, one from father
What are the monomers of nucleic acids? What is its directionality?
nucleotides with 3’ and 5’ directionality based on numbering of ribose sugar
Whta is a nucleotide?
nucleoside + phosphate groups
What is a nucleoside?
ribose (in RNA) or deoxyribose (in DNA) sugar + base
What is the nucleoside of adenine?
adenosine
What is the nucleoside of guanine?
guanosine
What is the nucleoside of uracil?
uridine
What is the nucleoside of cytosine?
cytidine
What is the nucleoside of thymine?
thymidine
What is the nucleoside in ATP?
adenosine
What are nucleotides important carriers of?
chemical energy (ie. ATP)
What are nucleotides in DNA and RNA linked by?
phosphodiester bonds
Which carbon would a nucleoside triphosphate be added to a growing nucleic acid?
3’
What are the levels of structure of DNA?
primary (sequence)
secondary (double-helix)
tertiary (chromatin)
What is the double-stranded DNA structure due to?
non-covalent interactions:
- H-bonds between bases
- stacking hydrophobic reactions
What features of Watson and Crick’s double helix model of DNA are energetically favoured due to increased entropy of
water?
the base pair cluster inside the double helix
What do stacking interactions in a double helix do?
help stabilize the strands and support the H-bonds between the bases
Describe base stacking interactions.
purine and pyrimidine bases are essentially hydrophobic
Why is DNA a double helix?
- sugar phosphate backbone (negatively charged) is hydrophilic, so
they face the solution - bases project towards the center, stacked one on top of the other, form a hydrophobic core, away from aqueous solution
- bases can H-bond with each other.
What are Chargoff’s rules of DNA base pairing?
purines are based with pyrimidines
- AT base pairs form 2 H-bonds
- GC base pairs form 3 H-bonds
Which DNA sequences would denature at the lowest temperature?
AT has fewer H-bonds therefore, the sequences with more As and Ts will denature at the lowest temperature
What do mutations lead bases to?
mismatch, disturbed geometry
Why are purines and purines not paired?
not enough space
Why are pyrimidines and pyrimidines not paired?
too much space
Describe the uniform structure of the general geometry of Chargaff’s base pairs.
purine-pyrimidine pair
- same distance between bases on the two strands
- same, regular hydrogen bonding pattern
- same stacking interactions between bases above and below
What are the structural differences between RNA and DNA?
- RNA: 2’ hydroxyl (OH) group DNA: 2’ H, lacks an O –> “deoxy”ribose
- RNA: AUGC
DNA: ATGC
What does the hydroxyl group of RNA do?
the additional OH (reactive functional group) makes RNA less stable than deoxyribose
What is DNA replication?
copying DNA for cell division
hereditary information is transmitted from generation to generation
What is transcription and translation?
genes provide the information to synthesize RNA or proteins for the cell
transcription: gene expression, DNA template transcribed to RNA
translation: protein synthesis, mRNA codons translated into protein primary structure
