Bio 120 Unit 4 Flashcards
Intro to the Cell Cycle
Cells arise through cell division of preexisting cells
Observations of newly developing organisms, or embryos, confirmed that plants and animals
-Start life as a single-celled embryo
-Grow through a series of cells divisions
Meiosis produces reproductive
cells called gametes
Mitosis produces all other cell types= somatic cells
Mitosis
Mitosis and meiosis are usually accompanied by cytokinesis- division of cytoplasm into daughter cells» Mitosis: Genetic material is copied and divided equally between 2 cells» Daughter cells are identical to the parent cell and to each other
Meiosis
Mitosis and meiosis are usually accompanied by cytokinesis- division of cytoplasm into daughter cells»Meiosis: Produces cells with half the amount of hereditary material as the parent cell» Daughter cells are genetically different
How do cells replicate?
Cells mush replicate for life to exist
1. Copying the DNA
2. Separating the copies
3. Dividing the cytoplasm to create 2 complete cells
The Cell Cycle has 4 Phases
The cell cycle is the
orderly sequence of events
that occurs from the
formation of a eukaryotic
cell through the
duplication of its
chromosomes to the time
it undergoes cell division
Cells alternate between M Phase & Interphase
M( mitotic) phase: Dividing
-Chromosomes are condensed into compact structures
Interphase: Nondividing
-G1+S+G2
-Chromosomes are uncoiled
-Cells are growing, preparing and fulfilling their specialized functions
-Cells spend most of their time in interphase
-The gap phase allow cells to grow and replicate organelles
Discovery of S Phase
Chromosomes replication occurs during the S(synthesis) phase of interphase
DNA Replication: S Phase of Interphase Chromosomes Condensation: M Phase
This is chromatin but by convention we still refer to this as the replication of chromosomes
What is a chromosome? A single long double helix of DNA
-Wrapped around proteins called histones
-DNA-Protein materiel is called chromatin
-DNA encodes the cells genetic info
A gene is a section of DNA
-Codes for s specific RNA
-Therefore codes for a specific protein
What happens during M Phase?
M Phase consist of 2 distinct events:
1. Mitosis- the division of the replicated chromosomes
2. Cytokinesis- the division of the cytoplasm
Every species has a characteristic number of chromosomes Humans have 46 chromosomes
Mitosis (M phase) is a continuous process with 5 subphases
- Prophase
- Prometaphase
- Metaphase
4.Anaphase
5.Telophase
Prophase: Chromosomes condense and first become visible in the light microscope
The spindle apparatus forms
-Move replicated chromosomes during early mitosis
- Pull chromatids apart in late mitosis
Prometaphase
-The nuclear envelope breaks down
-Microtubules attach to chromosomes at kinetochores
-Structure that form at the centromere
-2 form of the opposite side of each chromosome
-Microtubules that attach to chromosomes are called kinetochore microtubules
Chromosome are pushed and pulled by microtubules until they reach the middle of the spindle
Metaphase
-Mitotic spindle is complete
-Chromosomes are lined up on the metaphase plate
-Each chromosomes is held by kinetochore microtubules from opposite poles
-Astral microtubules hold spindle poles in place
Anaphase: Cohesins holding sister chromatids together split
-Sister chromatids are pulled by the spindle fiber toward opposite pole of the cell
-Creates 2 identical sets of daughter chromosomes
2 forces pull chromosomes apart:
-Kinetochore microtubules shrink
-Motor proteins of the polar microtubules push the 2 poles of the cell away from each other
Telophase
- A new nuclear envelop begins to from around each set of chromosomes
-The chromosomes begin to decondense
-Mitosis is complete when 2 independent nuclei have formed
Cytokinesis: Typically occurs immediately after mitosis
The cytoplasm divides to from 2 daughter cells
Cytokinesis in Plants
-Vesicles from the Golgi apparatus bring membrane and cell wall components to the middle of the cell
-These vesicles fuse to form a cell plate
Cytokinesis in Animals
-A ring of actin & myosin filaments contract inside the cell
-Pinches in to form a cleavage furrow and the ring shrinks and tighten until division is complete
Bacterial Cell Replication: Bacteria divide via binary fission
-This is a process similar to eukaryotes M Phase
-Bacterial chromosomes are replicated
-Proteins attach to chromosomes and separate them
-Other proteins divide the cytoplasm
Control of the Cell Cycle: Cycle length varies around cell types
-Mostly due to variation in G1
-Rapidly dividing cells essentially eliminate G1 Phase
-Non dividing cells are permanently in G1 phase( G0 state, highway exist)
Division rate can also vary in response to changing conditions
Kinase
Adds a phosphate group
Turns on protein
Phosphatase
Removes a phosphate group
Turns off a protein
Key regulator of cell cycle? MPF (M Phase Promoting Factor)
Kinases
-Cyclin Dependent Kinases(Cdk)
-They depend on cyclin to get activated
Cyclin
-Protein whose concentration cycles up and down during the cell cycle