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How do cells renew themselves?
through cell division
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True or false: all cells make copies of themselves in a growing embryo
True
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What types of cells are constanly regenerating through cell division?
- Skin
- Bone marrow
- Red and white blood cell
- and intestinal lining
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What cells cannot divide after birth ?
- Muscles
- Heart muscle
- Brain
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What are the steps of the Cell cycle?
- Mitosis (actual, active cell division)
- -prophase
- -metaphase
- -anaphase
- -telophase
- Interphase
- -G1 ("growth-1" or "gap-1")
- --G0 (quiescence)
- -S (replication of DNA)
- -G2 ("growth-2" or "gap-2")
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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
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G0 phase
- 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.
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S phase (synthesis)
- DNA is replicated (copied)
- All DNA must be duplicated in preparation for cell division
- this proccess takes about 8 hours
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G2 Phase
- 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
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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
- -prophase
- -metaphase
- -anaphase
- -telophase
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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
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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.
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Cells which have only one copy of each chromosome are called
- Haploid
- Only reproductive cells (spermand eggs) are haploids
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What is the number of a chromosome called?
"n"
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What is an example of a Diploid ?
Each daughter cell must have an appropriate amount of DNA: two copies of each gene
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True or False: The number of chromosomes (n) is related to, but not necessarily the same as, the DNA content.
True
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DNA Replication
- 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.
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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
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Whar is the term used for all parts of the cell cycle except mitosis?
Interphase
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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).
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True or false : all parts of interphase involve prepartation for, or recovery from mitosis.
True
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Prophase
- 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
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Metaphase
- 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)
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Anaphase
- 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.
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Telophase
- 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.
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What is Meiosis?
- a slightly different mechanism of cell division pertaining to germ cells
- Germ cells are those that can make new little humans
- -oocytes--ovum
- -spermatozoa
- 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
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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.
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_________ are points where homologous chromatids cross over.
Chriasmata
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True or false: Crossing over results in exchange of genetic information between member of homologous pairs.
true.
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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.
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True or false: there is virtually a 100% chance that crossing over will occur at one or more locations on the chromosome.
True.
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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.
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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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