Chromosomes, the cell cycle, and introduction to its regulation Flashcards
What does DNA form a complex with
RNA and proteins
What do DNA, RNA and proteins combine to form
chromatin
2 protein types in chromatin
Basic (mainly histones)
acidic
What else is chromatin associated with
PHospholipids
enzymes
other molecules
What is chromatin packed into
Bead like structures called nucleosomes
What does each nucleosome comprise of
2 loops of DNA double helix wrapped around a cluster of 8 histones
What are chromosomes formed from
The supercoiing and condensation of chromatin
What are genes
Specialised functional sites arranged along the chromosomes
Why are histones important
Important in compacting DNA and in chromatin regulation
What are the two forms of chromatin in interphase nuclei
Heterochromatin
Euchromatin
What’s heterochromatin
More condensed and densely staining.
Where is heterochromatin found
Near nuclear envelope
What does heterochromatin represent
Genes which are switched off
What are the two types of heterochromatin
Constitutive
Facultative
What’s euchromatin
less condensed and lightly staining
where is euchromatin found
more central location
What does euchromatin represent
genes which are switched on
What is constitutive heterochromatin
can’t get switched on
what’s facultative heterochromatin
can get switched on
What are the two stages of mitosis
karyokinesis
cytokinesis
Stages of karyokinesis
Prophase Prometaphase Metaphase Anaphase Telophase
What groups can the tissues of the body be divided into
Continuously renewing
Conditionally renewing (e.g. liver, kidney, endocrine glands)
Static or non-proliferative
How is the cell cycle regulated
1) Cyclin dependent kinases (CDK’s) bind to cyclin and become active
2) CDK’S cause phosphorylation to activate or inactivate target proteins
3) Proteins coordinate cell’s entry to next phase of cell cycle
How to inhibit cell cycle
the Kip family genes halt the cell cycle in G1 by binding and inactivating complex of cyclin and CDK (therefore its called a tumor suppressor)
In meiosis, what happens in prophase 1
leptotene zygotene pachytene diplotene diakinesis
what happens in leptotene
Chromosomes condense (not split into sister chromatids) -chromomeres are visible along their length
what happens in zygotene
- Homologous chromosomes (maternal-paternal) pair together to form bivalents
- chromosomes now split into sister chromatids and local sites of alignment (synapsis) develop between sister chromatids of homologous pairs
what’s a bivalent
pairing of homologous chromosomes
Another word for crossing over
chiasma formation
What happens in pachytene
synapsis is completed and crossing over occurs
- at chiasmata, genetic info exchanged between homologous pairs
- exchange more likely to happen between long stretches of chromatid arms than short ones
what’s diplotene
chromatids are held together by chiasmata as well as by the centromeres
What’s diakinesis
Chiasmata appear to move toward the ends of the chromatids
What’s the difference between male and female diplotene
In women, chromatids are held in this phase for decades
What’s metaphase 1
Each bivalent has 2 centromeres and these arrange themselves by chance on opposite sides of the metaphase plate
What happens in anaphase 1
- Chromosomes move to opposite poles of the cell.
- Each pole has a mixture of maternal and paternal chromosomes
What happens in telophase 1
- Each daughter cell has half the diploid number of chromosomes
- The nuclear envelope may reassemble before prophase 2 of the second meiotic division (meiosis 2)
What happens in meiosis 2
Similar to what happens in mitosis 2
-Centromeres now split at kinetochores. and sister chromatids move to opposite cells
Difference between gametogenesis in M AND F
sperm; four gametes produced
egg; forms one egg and 3 polar bodies
When is genetic variation introduced
- Pachytene; between homologous chromosomes at chiasmata
- Anaphase 1; Independent assortment
- Fertilisation
Different types of chromosome
Metacentric- when centromere is in middle of chromosome
Acrocentric- when centromere is not at middle
What’s a karyotype
Sum of all chromosomes in a nucleus arranged in size, location of centromere and arranged in homologous pairs
Main chromosomal abnormalities
Trisomy 21- 3x chromosome 21
Kleinfelters- HAve xxy sex
Turner’s syndrome- Xo have only one sex chromosome
