Nucleic acids 1-2 Flashcards
What is a nucleotide?
A sugar, phosphate and base bonded together.
What kind of bond holds the nucleotides together?
Phosphodiester
What kind of bond is between the base and the sugar?
Covalent
What kind of bond is between the two DNA strands?
Hydrogen
How many hydrogen bonds between cytosine and guanine?
3
How many hydrogen bonds between adenine and thymine?
2
Why do the sugar and phosphate head point outwards?
Because they are negatively charged.
How large is the human genome?
6x10^9 base pairs
What is a karyotype?
Organised profile of an individual’s chromosomes, including 22 pairs of autosomes and 1 pair of sex chromosomes.
What is chromatin?
A tightly packed complex of DNA, RNA and protein found in eukaryotes.
What are nucleosomes?
Protein complexes (histone) that are used to condense DNA into chromosomes so that it is able to fit into the nucleus. Provides a 7-fold condensation of DNA.
How many histone proteins is a nucleosome made up of?
8 ( 2 each of the following: 2A, 2B, 3 and 4)
How do histone proteins interact with DNA?
Histone proteins are positively charged so interact with the negatively charged sugar-phosphate backbone.
What connects each nucleosome to one another?
Histone 1
How is DNA replication semi-conservative?
The daughter cell inherits half of one DNA strand from the parent (template) and a newly synthesised one that is complementary to the template strand.
How does DNA helicase work?
Unwinds the double helix by breaking the hydrogen bonds holding them together. Energy is taken from the hydrolysis of ATP to ADP.
What does the sliding clamp do?
Surrounds DNA polymerase to make sure it does not fall off the strand.
What are RNA primers?
Direct DNA polymerase to where replication is needed. Transient so removed before replication is completed by exonuclease activity.
What is proof-reading?
A mechanism that reduces the mutation rate during replication of DNA. Before the next nucleotide, the previous nucleotide is checked for correct base pairing. If it is incorrect it is removed and replaced.
What is the mutation rate among human DNA replication?
1 every 109 base pairs
What occurs during prophase?
Supercoiling of chromosomes so that they are visible under a microscope.
What occurs during metaphase?
The condensed chromosomes align along the equator of the nucleus, drawn in by spindle fibres attached to the centromeres of the chromosomes.
What occurs during anaphase?
Microtubule spindle fibres separate homologous chromosomes in two (forming chromatids) and draw them to opposite poles of the nucleus.
What occurs during telophase?
Sister chromatids (now chromosomes once again) reach the poles and the nuclear membrane reforms around them.
What happens in cytokinesis?
Separation into two daughter cells.
What happens in G1 phase?
DNA is prepared to be replicated and cell growth occurs. (10 hours)
What happens in S phase?
DNA replication (9 hours)
What happens in G2 phase?
Checking of DNA replication (4 hours)
What is Watson-Crick base pairing?
The theory that a purine base must bind with a pyrimidine base but that each purine base binds to a specific pyrimidine base.
How many rings does a purine base have?
2
How many rings does a pyrimidine base have?
1
Which bases are purine bases?
Adenine and guanine
Which bases are pyrimidine bases?
Cytosine, thymine and uracil
What genetic material is present in prokaryotes.
Circular ‘chromosome’ called a genophore present in the nucleoid. Plasmids are also present.
