CHROMOSOMES, GENES AND THE CELL CYCLE Flashcards
how is human DNA packaged?
- into chromosomes within cells
what is a karyogram?
chromosomal constitution of a cell.
human karyogram constitution?
44 autosomes (22 pairs) and 2 sex chromosomes
describe the organisation of DNA
- made up of deoxyribose, phosphate, nitrogenous base
- double stranded, each complementary
- 5’ end = end of DNA or RNA chain, has phosphate attached to 5’ carbon
- 3’ end allows for synthesis of nucleic acid
- double helix shape
what is a gene?
all DNA sequences necessary to produce polypeptide
what is gene expression?
process by which sequence of bases in gene is converted to amino acid sequence
differences between DNA and RNA?
- RNA has uracil instead of thymine
- sugar is RNA is ribose not deoxyribose
- RNA is usually single stranded, DNA is double stranded
how is DNA arranged?
- double helix
- wrapped around nucleosomes, made up of core histones and link DNA
- twists around itself to form chromatic fibres
- loops around protein = scaffold
- chromatin fibre around scaffold loops around further to form chromosome
what are core histones?
histones can be associated with high conc of salt to form octameric histone core (histone proteins made of 8 subunits). these core histones are made of separate proteins; H2A,H2B, H3 and H4
What are the functions of chromosomes?
- dense packaging of DNA
- allows and coordinates DNA replication
- allows for correct division copies in mitosis
- allows recombination and correct independent assortment during meiosis
- allows for coordinated gene expression
homologous chromosomes
one chromosome from mother one from father. have same genes at same loci
sister chromatids
copy of the chromosome made during mitosis. when chromosomes doubled and joined at centromere = sister chromatids.
haploid
gametes; contain one pair homo chromosomes
telomeres
protective caps on chromosome ends consisting of 5-8bp tenderly repeating GC rich DNA sequences, prevent chromosomes fusing
telomerase
maintains telomere length in germ line cells
X-inactivation
one of the X chromosomes in females is inactivated for balanced gene expression. happens during development at blastocyte stage
G0 phase
cell left cell cycle and stops dividing.
interphase
changes take place in newly formed cells and its nucleus.
G1/S/G2
most of cell cycle
G1
increase proteins and organelles
S phase
synthesis. DNA doubled / DNA replicated.
G2 phase
period of protein synthesis and rapid cell growth
mitotic phase
nuclear division / karyokinesis.
prophase, metaphase, anaphase, telophase
cytokinesis
after mitosis, nuclei/cytoplasm divides
mitochondria
- oxidative phosphorylation
- cells have 200-100,000 mitochondria
- have own DNA, mostly coding
