Module 5 obj.15
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How do cells renew themselves?
through cell division
True or false: all cells make copies of themselves in a growing embryo
What types of cells are constanly regenerating through cell division?
- Bone marrow
- Red and white blood cell
- and intestinal lining
What cells cannot divide after birth ?
- Heart muscle
What are the steps of the Cell cycle?
- Mitosis (actual, active cell division)
- -G1 ("growth-1" or "gap-1")
- --G0 (quiescence)
- -S (replication of DNA)
- -G2 ("growth-2" or "gap-2")
G1 phase (first growth phase)
- After mitosis, a dividing cell enters this stage
- G1 takes 8-10 hours to complete
- if the cell is activelyt dividing, it prepares for the next division
- Cell duplicates organelles and cytoplasmic components
- In order to enter S phase, cell in must pass a checkpiont
- If a cell cannot pass the G1/S checkpoint, or if cell is quiescent (not actively dividing), cell remains in G0
- For example brain cells (neurons) spend a lifetime in G0
- Cells that take longe than the totalof 24 hours to pas through the cycle also wait in G0
- A liver cell divides onces every seven years spending all that time in G0 before passing onto S phase.
S phase (synthesis)
- DNA is replicated (copied)
- All DNA must be duplicated in preparation for cell division
- this proccess takes about 8 hours
- The cell finalizes its preparations for mitosis
- Cell now carries dougle the amount of normal DNA
- -in G1 had 46 DNA molecules, now has 92
- Duplication of centromeres
- Second checkpoint (G2/M) must be crossed
- -no normal cells are locked in G2
- After 4-6 hours cell enter mitosis
What is Mitosis?
- Mitosis is the actual active division of the cell
- Interphase is not a true phaseof mitosis, but all other parts of cell cycle
- -G1, G0, S, G2 are interphase
- mitosis has 4 stages
What is the difference between Mitosis and Cytokinesis?
- Mitosis is the process of nuclear division
- genetic material must be parcelled equally between cells
- chromosomes form, get pulled apart, dissolve
- Cytokinesis is the process of cell division
- plasma membrane between cells tightens like a rubber band and pinches of two cells where there was one before
- this separates the genetic material, cytoplasm and organelles into two equal daughter cells
What is DNA replication and which phase of the the cell cycle does it occur?
this is the copying of all the cells DNA molecules and it occurs in S phase.
Cells which have only one copy of each chromosome are called
- Only reproductive cells (spermand eggs) are haploids
What is the number of a chromosome called?
What is an example of a Diploid ?
Each daughter cell must have an appropriate amount of DNA: two copies of each gene
True or False: The number of chromosomes (n) is related to, but not necessarily the same as, the DNA content.
- 92 molecules are packed int 46 chromosomes
- When the chromatids are ripped apart at anaphase, each daughter cell gets 46 DNA molecules
- DNA strands separate
- Two New DNA strands (teal) constucted using orginal strands as template
- Same base paringa rules allow new strands to be made with exact fidelity.
Okazaki fagments and DNA Replication
- The two strands of DNA double helix are anti-parallel
- -One runs 5'--3' left to right; other runs 5'--3' right to left
- DNA is only "built" 5'--3'
- As DNA is copied (replicated), two different strategies are used
- -Leading strand built continuously 5'--3'
- -Lagging strand uses Okazaki fragments to build short segments which are then stitched together
Whar is the term used for all parts of the cell cycle except mitosis?
During interphase, the DNA is loosely packed sot that it may be transcribed to RNA as needed. this is called
Euchromatin ("perfect" or "good" chromatin; chromatin refers to the colored material in the cell).
True or false : all parts of interphase involve prepartation for, or recovery from mitosis.
- DNA is tightly packed into chromosomes
- The nuclear envelope breaks down
- The mitotic spindles form (grow out of the centrosome, made of microtubles uste to move chromososmes
- The middle phase of mitosis in which everything in the parent cell lines up in the middle
- Chromosomes move to the middleof the parent cell
- Microtubles of the mititic spindle attach to anchors(centromeres) found in the middle of each chromosome
- Phase of cell cycle use t create a karyotype- a pictuer of the chromosomes that is used to diagnose trisomy 21 (Downs syndrome)
- The chromatids (arms of chromosomes) are torn apart into two equal pieces by the action to the mitotic spindles
- The chromatids then back up and take their places in either ent of the elongating cell.
- Mitosis is completed
- A cleavage furrow appears in the middle f the parent cell
- As the furrow deepens, the cell is split into two daughter cells.
- In each of the daughter cells, the nuclear envelope refrom and the mitotic spindle comes apart.
What is Meiosis?
- a slightly different mechanism of cell division pertaining to germ cellsGerm cells are those that can make new little humans
- these join at fertilization
- if fertilized egg has normal DNA complement, then each germ cell needs 1/2 normal DNA
- Normal DNA content of all non-germs cells in the body are diploid
- Germ cells with 1/2 normal DNA: haploid
How does Meiosis differ from Mitosis?
- 1.Meiosis is a reduction division
- -in mitosis, normal DNA complement is preserved
- -in meiosis I, DNA content of each daughter cell is halved
- 2. Crossing over is an important feature
- -chromatids from the same region of the same chromosome "swap"and the DNA is scrambled in this way.
_________ are points where homologous chromatids cross over.
True or false: Crossing over results in exchange of genetic information between member of homologous pairs.
Why is crossing over a major advantage of sexual reproduction?
- This scambles the genetid materal so that each sibling, even in a large family, has a different compliment of DNA.
- A "suffleing" of genetic material.
- Without it, some siblings woudl be identical twins just born in different years.
True or false: there is virtually a 100% chance that crossing over will occur at one or more locations on the chromosome.
What is the physical distance between genes called?
- Centimorgan (cM)
- A distance between gene a and gene b of one centimorgan is a 1% chance that crossing over will occur
- In physical terms a centimorgan is about 1 million bases of DNA.
How does gene maping relate to Meiosis?
- Crossing over is also used as a tool to determin the physical location of genes.
- if they are close together then crossing over almost never occurs between two neighbor genes
- If they are far apart, it almost always occurs
- A 1% chance of crossing-over (recombination) is called 1 centimorgan (1cM)
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