Chromosomes, Genes and DNA Flashcards
Describe solenoid structures
Fibres compacted into several hierarchal loops to create highly condensed structures - chromosome visible under light microscope in nucleus during cell division. Genes cannot be expressed when solenoid (heterochromatin)
What are histones?
Proteins around which DNA molecules are wrapped. Positively charged in order to be complementary to negative P groups on DNA.
Which bonds link nucleotides?
Phosphodiester bonds
Distinguish between purines and pyrimidines
Purines - two ring structure e.g. G and A
Pyrimidines - one ring structure e.g. T, C and U
Number and type of bonds between nitrogenous bases?
A-T has two bonds, C-G has three bonds, A-U has two bonds. H bonds between them all
Which base pairs are responsible for major and minor grooves?
G and C
Outline the cell cycle
G1 - cell prepares for DNA replication
S - DNA replication
G2 - cell prepares for cell division (double checking DNA)
M - cell division (mitosis)
G0 - cell just performing its normal function
What does dNTP stand for?
Deoxyribonucleoside triphosphate
In which direction does DNA replication occur?
5’ to 3’ end
What does mitosis result in?
Two genetically identical daughter cells (identical chromosomal content)
What does meiosis result in?
Four genetically different haploid cells
Describe initiation in DNA replication
Recognition of origin of replication, DNA polymerase recruited alongside some other proteins, kick start by primase
Describe elongation in DNA replication
Moving replication forks, helicase unwinds double helix, DNA polymerase extends 3’ end only, DNA ligase joins fragments
How does variation arise in meiosis?
Independent assortment of chromosomes and crossing over
Describe termination in regards to DNA replication
DNA ligase joins final fragments, chromosome number stays the same, one replicated chromosome consists of the two sister chromatids
What is the main difference between spermatogenesis and oogenesis?
Spermatogenesis results in 4 sperm cells whereas oogenesis results in 1 mature ovum and 3 polar bodies
Draw out pedigree symbols
Square - male, circle - female, filled - affected, unfilled - unaffected, half filled/dot - carrier, diamond - unknown gender, diagonal line through - deceased
Describe characteristics of autosomal recessive traits
Heterozygotes are unaffected, males and females equally affected, 25% chance of affected offspring, two affected individuals will have affected offspring only, can skip generations, both parents have to be carriers e.g. CF
Describe the characteristics of autosomal dominant conditions
Heterozygotes are affected, males and females are affected equally, rarely found in homozygous state - too severe and sufferers die, every affected individual will have at least one affected parent, disease cannot skip generations
Describe the characteristics of X-linked conditions
Hemizygous males and homozygous females are affected, more common in males, heterozygous female carrier has 50% chance of getting, affected males cannot pass trait onto sons, daughters of affected males are heterozygous
What is linkage?
When genes on different chromosomes show independent assortment during meiosis - if two genes are close together then they can become linked and co-segregate
What is the RNA stem-loop structure?
Single stranded RNA loops back on itself, thus one side will run anti parallel and H bonds will form between complimentary bases
Describe the key features of DNA double helix
2 independent polymers, complementary, anti-parallel, one complete turn in 10 bases, 0.34nm space between base pairs, purine and pyrimidines are planar and unsaturated, major and minor grooves
Describe mitotic chromosomes
Highly condensed fibres. Unexpressed genomes - cannot replicate
