Lecture 10 Flashcards
Bacterial cell division called
Binary fission
Cell cycle
Grow and replicate DNa> divide , repeat
Cell division in a nutshell
Replicate DNA then divide
Eukaryotic cell cycle
Grow> replicate DNA> grow some more> divide
Repeat
Interphase stages
G1- cell grows and prepares for S phase (G stands for Gap”
S- synthesis of DNA. DNA replicated to make a complete copy
G2- cell grows and prepares for mitosis
G1
Cell grows and prepares for S phase
G stands for gap
Interphase stage
S stage interphase
Synthesis of DNA. DNA replicated to make a complete copy
G2 interphase
Cell grows and prepares for mitosis
G0 aka G naught
Resting state. Not actively dividing or preparing to divide
Prokaryotic cell cycle
Single circular chromosome is pulled apart during replication
During cytokinesis, membrane constricts and new cell wall is formed between daughters
Very fast (as little as 10 minutes), so the stages basically overlap instead of being separated over time like in eukaryotes
Replication of eukaryotic chromosomes create what
2 sister chromatids
Centromères
Hold together chromosomes and chromatids at the center
Haploid vs diploid
1 set of DNA ( purple)
Vs
1 set of homologous chromosomes. 1 from mom (red) and 1 from dad (blue)
Mitosis phases
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis
Prophases
Chromosomes condense and become visible
Nuclear envelope begins to break down
Spindle starts to form
Prometaphase
Nuclear envelope breaks down
Chromosomes attach to microtubules and moved to mid zone
Metaphase
Chromosomes attached to microtubules and align at the metaphase plate
Anaphase
Sister chromatids separate and move to opposite poles of the cell
“Aaaaaaahhhh naphase. Ripping apart”
Telophase
Chromosomes decondense
Nuclear envelope reforms around daughter nuclei
Spindle fibers disappear
Cytokinesis
Division of the cytoplasm. Typically begins during late anaphase or telophase. Resulting in 2 daughter cells
Nucleosome
A protein complex consisting of histone proteins that DNA wraps around
Microtubules in the animal spindle
Kinetochore microtubules- move chromosomes around
Non-kinetochore- hold spindle together and control its length
Astral microtubules- spindle positioning and length control
Where at the spindles Positive and negative?
+ in equator
- at the poles
Kinetochore microtubules attach to what
Kinetochore of each sister chromatid
Centromere
Constricted region of chromosome linking sister chromatids
Kinetochore
Complex of proteins
2 mechanisms of anaphase
Anaphase A: kinetochore MTs shorten (chromatids move to poles)
Anaphase B: non Kinetochore MTs slide apart (spindle elongates)
Mechanism of poleward chromosome movement during anaphase
Microtubules motor protein “walks” along microtubules and it disassembles as the Kinetochore passes over it
Mitosis things to pay attention to. To determine what phase
Chromatin: condensed or not?
Nuclear envelope: present or not?
Centrosomeres(animals): replicated? Position?
Chromosomes: position? Attachment to microtubules? Sister chromatids attached?
Cell cycle / mitosis
Interphase G1
Interphase G2
Prophase
Prometaphase
Metaphase
Anaphase
Telophase+ cytokinesis
Repeat
Cytokinesis in animal cells
Cleavage furrow forms as the contractile ring pulls membrane in like a drawstring until it eventually pinches the 2 cells apart
Contractile ring consists of microfilaments
Prophase summary
DNA condensed
Nuclear envelope begins to break down
Centrosomes (animal cells) duplicated and migrating to poles
Prometaphase summary
Nuclear envelope gone
MTs “search and capture” chromosomal kinetochores
Move them towards spindle midzone
Centrosomes migrating to create 2 poles
Metaphase summary
Replicated chromosomes are attached to MTs
Aligned at metaphase plate
Spindle is bipolar
Anaphase summary
Sister chromatids separate
Pulled towards poles (as Kinetochore fibers shorten)
Spindle elongates (as Kinetochore MTs slide apart)
Telophase summary
Nuclear division (karyokinesis) is complete
Spindle disassembles
Chromosomes decondense
Nuclear envelope reforms in each daughter cell
Cytokinesis summary
Overlaps with telophase / late anaphase
Ends when daughter cell completely separated (each having own plasma membrane and cytoplasm)
Mitotic spindle in plants
No centrosomes, so spindles tend to be broader at poles
“Acentrosomal spindles”
Cytokinesis animals vs plants
Animal divides out to in (Luke a rubber band around it)
Plant divides in to out: cell plate starts growing in the middle and cuts across
Sexual reproduction
-produces genetic variation which is the basis for evolution
Genetic diversity in a population allows adaptation to changes in environment
Meiosis is the source of this genetic variation
Meiosis purpose
Generate genetic variability by shuffling DNA
Creates egg and sperm (gametes)
Gametes only have one copy of each chromosome (haploid)
Diploid life cycle
1n > fertilization > 2n > meiosis
Repeat
Diploid life cycle in most animals
Meiosis> gametes 1n > fertilization > zygote 2n > mature 2n > meiosis
Repeat
Meiosis vs mitosis
Mitosis: 2n > creates 2 2n cells
Meiosis: 2n > 2 1n cells > each producing 2 1n (4total)
Naming convention for chromosome numbers
Haploid vs diploid numbers
1 chromosome:
*1 haploid number (1n)
* 2 diploid number (2n)
2 chromosome:
* 2 haploid number (1n)
* 4 diploid number (2n)
And so on
How does meiosis increase genetic diversity
By mixing/ recombining chromosomes
