DNA Intro Flashcards
What is heterochromatin and euchromatin?
Heterochromatin - (solenoid) tightly wound around histones - darker patches - genes not expressed
Euchromatin - loosely wound DNA - lighter patches - genes expressed
What are the 3 opponents of a nucleotide
Sugar, phosphate, base
What’s the difference between the major groove and minor groove?
The strand backbones are closer together on one side of the helix than on the other. The major groove occurs where the backbones are far apart, the minor groove occurs where they are close together. The grooves twist around the molecule on opposite sides
How much DNA is in one cell?
DNA width is 2nm but the total length is 2m per cell
Define histone
Histones are a family of basic proteins that associate with DNA in the nucleus and help condense it into chromatin. Nuclear DNA does not appear in free linear strands; it is highly condensed and wrapped around histones in order to fit inside of the nucleus and take part in the formation of chromosomes.
How does DNA bind to histones?
Histones are basic proteins, and their positive charges allow them to associate with DNA, which is negatively charged. Some histones function as spools for the thread-like DNA to wrap around.
What is a nucleosome?
Under the microscope in its extended form, chromatin looks like beads on a string. The beads are called nucleosomes. Each nucleosome is made of DNA wrapped around eight histone proteins that function like a spool and are called a histone octamer. Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3, and H4. The chain of nucleosomes is then wrapped into a 30 nm spiral called a solenoid, where additional H1 histone proteins are associated with each nucleosome to maintain the chromosome structure.
Describe genes
What? Genes carry the code for proteins Where? Genes have a chromosomal location How many? Humans have about 25,000 genes Fruitfly has about 15,000 genes E.coli has about 4,500 genes
What is a genome?
What? Genome is the entire DNA sequence Human Genome is 24 chromosomes (22 plus 2 sex chromosomes X and Y) Genes are on the same chromosome on the same location in each individual
How many chromosomes in the human genome
22 autosomal
2 sex chromosomes
What is a nucleic acid?
Nucleic acids are ‘polynucleotides’ = linear polymers of nucleotides
What’s the difference between a nucleotide and a nucleoside?
A nucleoside consists of a nitrogenous base covalently attached to a sugar (ribose or deoxyribose) but without the phosphate group. A nucleotide consists of a nitrogenous base, a sugar (ribose or deoxyribose) and one to three phosphate groups
What’s the difference between ribose and 2-deoxyribose?
2-deoxyribose has a H on C2 rather than OH
What charge does a phosphate group. Have
-ve
What are the 2 types of nitrogenous base?
Purine (2 C ring) - A and G
Pyrimidine (1 C ring) C T and U
Give an example of a ribonucleotide
AMP
Give an example of a deoxyribonucleotide
dAMP
Name each nucleotide/nucleoside of ATCGU using nucleic acid nomenclature
Base Nucleoside Nucleotide Adenine (A) Guanine (G) Uracil (U) Cytosine (C) Adenosine Guanosine Uridine Cytidine Adenosine monophosphate (AMP) Guanosine monophosphate (GMP) Uridine monophosphate (UMP) Cytidine monophosphate (CMP)
In DNA: Base Nucleoside Nucleotide Adenine (A) Guanine (G) Thymine (T) Cytosine (C) Deoxyadenosine Deoxyguanosine Deoxythymidine Deoxycytidine Deoxyadenosine monophosphate (dAMP) Deoxyguanosine monophosphate (dGMP) Deoxythymidine monophosphate (dTMP) Deoxycytidine monophosphate (dCMP)
What type of bonds join nucleotides?
Phosphodiester
What are the 2 ends of the chain
5’ P
3’ OH
How do base pairs bond?
A-T (2 H bonds)
C-G (3 H bonds)
A-U (2 H bonds)
What measures the length of a bond?
Angstroms
How do DNA strands run in relation to each other
Antiparallel
What is the convention of reading dna strands
5’ to 3’ left to right unless otherwise stated
What is an equation to explain DNA replication
(dNMP)n + dNTP —-> (dNMP)n+1 + PPi
D = dna N = any M = mono P = phosphate T = tri
Describe the model or dna replication
- separation of DNA strands
- stepwise reaction
- reaction driven by pyrophosphate hydrolysis
- chain growth is directional, from 5’ to 3’
Describe dna replication in prokaryotes
Initiation
• Recognition of origin of replication
• Requires recruitment of DNA polymerase plus other specific proteins
• Requires a ‘kick-start’ by primase (as DNA polymerase can only extend a 3’end)
Elongation • Moving replication forks • Helicase unwinds double helix • DNA polymerase extends 3’ ends only leading to leading strand (continuous), lagging strand (discontinuous) and Okazaki fragments • DNA ligase joins fragments
Termination
When two facing replication forks meet and DNA ligase joins the final fragments
