DNA and DNA packaging Flashcards
What is the chemical structure of guanine?
What is the chemical structure of cytosine?
What is the chemical structure of adenine?
What is the chemical structure of thymine?
What are pyrimidines?
A type of base derived from a six-membered pyrimidine ring i.e. C, T and U
What are purines?
Bases that have a second five-membered ring fused to the first six-membered ring, i.e. A and G
How many hydrogen bonds are there between adenine and thymine/uracil?
2
How many bonds are there between guanine and cytosine?
3
What is nucleic acid?
Any of a group of long, linear macromolecules, either DNA or various types of RNA, that carry genetic information directing all cellular functions: composed of linked nucleotides
What are the two main types of nucleic acid?
Ribonucleic acid and deoxyribonucleic acid
What is a nucleoside?
A sugar (ribose/deoxyribose) covalently attached to a base
What is the general chemical structure of a nucleotide?
What do the 5’ and 3’ ends correspond to in DNA?
The 5’ indicates the end with a phosphate group and the 3’ the end with the hydroxyl group
The two strands in DNA run _____ to one another
Antiparallel
What type of bonds link the sugars together in the sugar-phosphate backbone?
Phosphodiester bonds
What novel bases are involved in methylation and demethylation of DNA as a means of regulatory control?
5mC (5-Methylcytosine) and 5hmC (5-Hydroxymethylcytosine)
Approximately how many nucleotides are there in the human genome?
6x109in 46 chromosomes
What proteins assist in chromosome packaging?
**Histones **and non-histone chromosomal proteins
What is chromatin?
DNA that is wrapped around protein complexes
What type of packaging are histones associated with?
The nucleosome, which has a ‘beads on a string’
What is a nucleosome core particle?
One unit in the nucleosome, which consists of a histone octamer and DNA wrapped around it two times
How many proteins make up a histone?
8, two lots of:
- H2A
- H2B
- H3
- H4
What is the next stage of DNA packaging after the nucleosome?
Chromatin fiber
What does the chromatin fiber form of packaging depend on?
A 5th histone protein called **H1 **which is thought to pull the nucleosome into a regular repeating array
Chromatin fiber can be further condensed into _________ _________
Lampbrush chromosomes
What is the structure of a lampbrush chromosome?
The 30nm chromatin fiber loops out and attaches to a central scaffold.
During ________, lampbrush chromosomes condense even further into ________
During prometaphase, lampbrush chromosomes condense even further into chromatids
Define heterochromatin
Highly condensed chromatin visible by light microscopy in interphase eukaryotes
Define euchromatin
Less condensed chromatin that contains 30 nm fibers and loops.
At what stage do chromosomes become visible in the eukaryotic cell?
Metaphase
