Unit 2 Chapter 11: The Cell Cycle + Mitosis Flashcards
What are the 3 mysteries of heredity
- all organisms come from other organisms
- children resemble their parents
- siblings are not identical
What is the cell theory (3 points)
- all organisms consist of cells
- cells divide to produce new cells
- higher organisms fuse their cells to produce a new organism
What are mitosis and cytokinesis responsible for (3 events)
- growth
- wound repair
- reproduction
What is asexual reproduction
produces offspring that are genetically identical from the parent, ie. mitosis
What is a chromosome
- a single string of DNA
- linear in eukaryotes
- circular in bacteria
What does DNA do
stores the cell’s heredity info or genetic material
What is a gene
a length of DNA that codes for a particular protein or RNA found in the cell
Why can we see chromosomes
they condense by associating with histones (proteins) and forming chromatin
What is a chromatid
one of the DNA copies in a replicated chromosome
What is a centromere
the specialized region that joins 2 chromatids togethe
What are sister chromatids
chromatids from the same chromosome
What is a karyotype
a way of organizing and identifying chromosomes
What are homologs
nearly identical pairs of chromosomes
What are mitotic chromosomes
2 chromosomes bound by a centromere (technically thats 2 pieces of DNA but we still call them chromosomes)
What does “segregating is exacting mean”
- organisms need at least 1 of each chromosome because each has specific genetic material
- usually we need EXACTLY one of each
What is the cause of down syndrome
3 chromosome 21
What is interphase
DNA is found in nucleus associated with histones (as chromatin)
- active time: cell is either growing and preparing to divide or performing its specialized function
- includes S phase
What is S-phase
- in interphase
- DNA is replicated
What is G2
the time lag that occurs after S phase and before M phase
What is G1
the time lag that occurs after M phase and before S phase (longer than G2)
Why are G2 and G1 necessary
the cells need to grow and synthesize enough organelles so its daughter cells will be normal in size and function
What is mitosis
the process where cells divide to make identical copies of themselves and each daughter cell inherits one copy of each chromosome
What do cohesins do
protein rings made of 3 subunits that encircle 2 pieces of DNA to keep them together until they receive the division signal
What do condesins do
protein rings made of 3 subunits that encircle DNA and stabilize loops in the same piece of DNA (to make them smaller/more condensed)
What are the steps of mitosis
IPPMAT
- interphase
- prophase
- prometaphase
- metaphase
- anaphase
- telophase/cytokinesis
What happens in prophase
-chromosomes condense
-spindle apparatus forms
(centrosomes move to poles)
What is the spindle apparatus
- consists of microtubules (polar and kinetochore)
- produces forces that pull chromosomes to poles and push cell poles away from eachother
What are polar microtubules
extend from each spindle (centrosome which contains centrioles) and overlap each other in middle of cell
What are kinetochore microtubules
attach to chromosomes (kinetochore, at centromere region)
-each chromosome has 2 kinetochores
What happens in prometaphase
- nuclear envelope disappears
- kinetochore microtubules attach to one of the 2 sister chromatids of each chromosome at the kinetochore
- centrosomes continue moving to poles, kinetochore microtubules start moving chromosomes to center
What happens in metaphase
- cells line up in centre (metaphase plate)
- polar microtubules create this pole to pole connection by overlapping
What happens in anaphase
- cohesins split
- sister chromatids are pulled apart to opposite poles (replicated chromosomes separate into 2 identical sets of unreplicated chromosomes)
What happens in telophase/cytokinesis
- nuclear envelope reforms
- spindle apparatus disappears
- chromosomes decondense
- 2 nuclei form
- cell pinches off and divides (cleavage furrow) (actin and myosin)
What is cytokinesis like in plants
vesicles from golgi line up and from a cell plate which builds up and divides the 2 cells
Which ends of the microtubule attach to the kinetochore
plus end
How do chromosomes move during mitosis
- the kinetochore microtubules shorten because tubulin subunits are lost from plus ends
- as anaphase occurs, proteins in kinetochore catalyze the loss of tubulin subunits at plus ends of the tubules, while proteins walk towards minus end
- this pulls chromosomes to opposite sides of the cell
What type of cells does mitosis produce
diploid
How is the cell cycle regulated
various cyclins which are the second MPF (mitosis promoting factor)subunit
- cyclin concentrations fluctuate throughout the cell
- protein kinase subunit of MPF is cyclin-dependent kinase
- cyclin functions as regulatory protein and kinase catalyzes the phosphorylation of other proteins to start mitosis
How is MPF activated
when one of the phosphate groups on the Cdk subunit drops off in G2 and causes shape to change
How is MPF deactivated
during anaphase, enzymes degrade MPF’s cyclin subunit which leads to its own destruction
What is the G1 checkpoint
-between G1 and S phase
-establishes whether cell will continue through cycle and divide or go to G0
factors:
-size-cells are arrested if too small
-availability of nutrients-arrested if nutrient conditions are poor
-social signals
-damage to DNA
-if damaged DNA is not stopped, can lead to uncontrolled cell division, cells will enter cell cycle without growing getting smaller each time
What is the G2 checkpoint
-after S phase and between G2 and M phase
-if DNA is damaged or not replicated correctly, cells can’t pass
-size could also be a factor
-
What is the S to G2 checkpoint
- ensures cells are replicated
- hydroxyurea blocks chromosome replication so cells stay in S phase
- caffeine disables this checkpoint
What happens when both hydroxyurea and caffeine are added
DNA cannot replicate, still enters mitosis and then everything dies
What is the metaphase checkpoint
- if not all chromosomes attach to spindle properly, mitosis stops at metaphase
- anaphase delayed until everything attaches properly
What is cancer and how does it arise
- the uncontrolled division of cells
- arise from cells in which cell checkpoints have failed
What are the 2 defects of cancerous cells
- defects that make proteins required for cell growth active when they shouldn’t be
- defects that prevent tumor suppressing genes from shutting down the cell cycle
How do cells become malignant and cancerous
if they can detach from the original tumour and invade other tissues
What is the G0 phase
-where mature cells go, when their cell cycle is arrested in G1
Which check point is most crucial when it comes to cancer
G1 because it looks for external signals which can be manipulated
What is cancer characterized by
- loss of control at G1 checkpoint which leads to crazy cell division
- metastasis
Progression through the cell cycle is regulated by oscillations in the concentration of
cyclins
What signals a cell to divide
the binding of Cyclin D (only in G1) and Cdk4 (always in cell)
Which cells don’t bother with cytokinesis
muscle cells
How many chromosomes do humans have
46, 23 pairs
