Lecture 4 Flashcards
What are the stages of the cell cycle
M, interphase
What is interphase?
S stage g stage
M stage
Mitosis, cell division
S stage
Synthesis, rep of DNA
G stage
Gap stage
G1 - cell grows after mitosis
G2 - prepare for mitosis
G0 - after G1, a resting phase
Purpose of cell division
Single celled - increase cell number
Multicellular - build tissues and organs
What is Binary fission
cell division in bacteria
How does binary fission work?
After replication, chromosomes are transported to poles
Tubulin like molecule forms a ring in equatorial plate of cell
Ring grows inwand and separates mother cell into 2 daughter cells
Stages of mitosis
Interphase Prophase Metaphase Anaphase Telophase
What do chromosomes look like during interphase
Decondensed, look strand like
Referred to as chromatin
T/F in interphase, chromatin are all orderly structured into territories
True
Transcription factories
active genes from several chromo-somes may be localized to specific regions with high transcription activity
Describe DNA condensation
After dna replication, a lnear strand of dna coils around histone proteins which coild more and more and forms a chromatid
What does a replicated chromosome look like
Like an x, with two sister chromatids
Each chromatid are identical
Held together at centromeres
Centromere
specialized regions of a chromosome
Has kinetochores on outside
kinetochore
Acts as docking platform for mitotic spindles to attach to
Cohesin
hold sister chromatids together
Centrosomes
Microtubule organizing centres in animals
What do mitotic spindles do?
attach to centromere and pull chromatids to the poles
What happens in interphase
Chromosomes are decondensed chromatin
Dna replcates
Nuclear membrane exists
What happens in prophase
Chromatin condensed into chromosomes
Nuclear membrane dissolves
Cohesin holds sister chromatids together
What happens in metaphase
Mitotic spindle formation completes
Microtubules attach to chromatids
Condensin further compacts the chromatin
What happens in anaphase
Cohesin degrades, sister chromatds are pulled apart, move to opposite ends of cell
n value
Number of chromosomes in a cell
C value
Amount of dna in base pairs
What is 1c?
The amount of dna in a haploid cell
In somatic cell, whats the c value during g1 phase?
2c
In somatic cell, whats the c value during s phase?
Gradually rises to 4c, because dna is replicated, amount doubles
In somatic cell, whats the c value during g2 phase?
4c
In somatic cell, whats the c value during m phase?
Stays 4c until very end, where it becomes 2c, since the chromosomes separate
How many chromosomes in human somatic cells
46
Describe gametocytes before meiosis in terms of c value and n value
2n and 4c
So their chromosomes are duplicated, have 2 identical sister chromatids
What happens in meiosis 1
Homologous chromosomes are paired into tetrads
These tetrads are pulled apart, 1 duplicated chromosome goes to each pole
2 daughter cells form, with half the number of chromosomes as the parent cell
Describe daughter cells after meiosis 1 in terms of c value and n value
1n and 2c
What happens in meiosis 2
Same as mitosis, chromosomes are lined on equatorial plate, sister chromatids pulled apart into different daughter cells
Describe daughter cells after meiosis 1 in terms of c value and n value
1n and 1c
Describe crossing over during meiosis 1
Nonsister chromatids of homologous chromosomes are held together
Chiasma forms
The chromosomes exchange genetic information
Chiasma
Spot where nonsister chromosomes of homologs attach to each other
