Molecular genetics - DNA Flashcards
What are the three components of nucleotides
Deoxyribose sugar, Phosphate group, nitrogenous base
What are purines?
Double ringed structures. Guanine and Adenine
What are purines?
Single ringed structures. Thymine, Uracil and Cytosine
What are the three bonds on DNA’s backbone?
Glycosyl, phosphodiester, hydrogen bonds
The 2 DNA strands are ______ but are ______
not identical, complementary
How do complementary bases bond?
Purine to pyrimidine
What are the complementary bases?
Adenine to Thymine (or Uracil in RNA), Cytosine to Guanine
What is Chargaff’s rule?
% composition of Adenine is the same as that of Thymine and % composition of Cytosine is the same as that of Guanine
What does it mean that DNA strands are antiparallel?
The two strands run in opposite directions, one runs 3’ to 5’ and the other 5’ to 3’
How big is one turn of the helix?
3.4nm
What is the distance between nucleotides?
0.34
How many nucleotides in one turn of the helix?
10
What is the diameter of the helix?
2nm
Genome
Complete genetic make-up of an organism
Gene
Basic unit of heredity. Functional units of DNA. The coding sequences for proteins.
Nucleoid
Structure in prokaryotes that contains the chromosomal DNA
Regulatory sequence
A sequence of DNA that regulates the activity of a gene
Where is DNA found in prokaryotes?
In one circular chromosome, the nucleoid
The nucleoid is made of supercoiled DNA. What controls that supercoiling?
Topoisomerase I and Topoisomerase II
What is the point of antibiotics
To inhibit topoisomerase
Where is eukaryotic DNA found
Nucleus
Histone
A protein that helps to compact DNA
Nucleosome
The condensed structure formed when double stranded DNA wraps around an octamer of histone
Chromatin
Non-condensed form of genetic material made of DNA and proteins. This is how DNA fits in a cell
What must DNA be able to do efficiently
Replicate with a high degree of accuracy and code for production of proteins by the cell
What happens during Mitosis?
Cells divide into 2 daughter cells with identical DNA
What method of replication does DNA use? Explain it
Semi-conservative replication. One strand of the DNA is used to create the second one
Explain the initiation phase of DNA replication
A portion of the double helix is unwound and the bases are exposed for base pairing
Explain the elongation phase
2 new strands of DNA are assembled using the parent DNA as a template. New strand and old strand for helices
Termination phase
Replication process completed & the two strands separate from each other. Replication machine disassembled.
Helicase
Unwinds parent DNA
DNA primase
Synthesizes DNA primer to generate Okazaki fragments
Single Stranded Binding Proteins (SSBPs)
Helps to stabilize single-stranded regions of DNA when it unwinds. Prevents annealing
Topoisomerase II
Relieves strain on parent chain generated by the unwinding of the two strands
DNA polymerases
Synthesizes new Daughter strands, removes RNA primers and fills the gaps from Okazaki fragments. Proofread new DNA
Ligase
Joins the ends of Okazaki fragments in lagging strand fragments
Primer
Short segment of RNA that is complementary to a part of the 3’ to 5’ DNA template strand and serves as a starting point for additional nucleotides.
Replication bubbles
There are many origins to DNA replication, which forms many replication forks. They end up looking like bubbles
In what direction is DNA synthesized? Why?
5’ to 3’ because the enzyme binds to the parent strand at the 3’ end
What is the role of DNA polymerase in the elongation phase?
To proofread
What is the role of ligase in the elongation phase?
To stitch together okazaki fragments
Okazaki fragments
Short DNA fragments generated during synthesis of the lagging strand in DNA replication
Mismatch repair
mechanism for repairing errors made during DNA replication. A group of proteins recognize an error and therefore replace the the nucleotide
Do prokaryotes or eukaryotes have a faster replication rate?
Prokaryotes, 1000 nucleotides per second added as opposed to eukaryotes’ 40 nucleotides per second
How many polymerase enzymes in prokaryotes?
5
How many polymerase enzymes in eukaryotes?
13
Telomere
Repetitive section of DNA near the end of each chromosome. This helps to prevent the loss of important genetic information during the replication of linear eukaryotic DNA
