Transcript Centrosomes and Centrioles

Centrosomes and Centrioles
• Centrosomes organize microtubules
• Centrioles: bundles of microtubules
– Pull chromosomes, form core in cilia
Cilia and Flagella
• Motor proteins
• 2:9 microtubule
pattern
• Cilia move fluids
• Flagella move sperm
cell
Membranous Organelles: Create cell
compartments
• Internal lumen and membranes for protected reactions
• Mitochondria: Generates cell energy (ATP) , have DNA
Endoplasmic Reticulum (ER) & Ribosomes
• Smooth ER: Lipid synthesis & conversion
• Rough ER: Ribosomes, protein assembly & transport
vesicles
Cell Growth and Reproduction
• Cell Cycle- the series of changes
• Two Phases
– Interphase: Cell grows and carries on its usual
activities
– Cell division or mitotic phase: cell divides into two
daughter cells
Cell Life Cycle:
Interphase or Growth Phase (G1, S, G2) - “betweenphases”, prepares for mitosis by duplicating DNA and
organelles
S phase: DNA replication. New
histones are made and
assembled into chromatin
G1 : The cell is
metabolically
active,
synthesizing
proteins and
growing
G2 Very brief.
Enzymes and
other proteins
synthesized. By
the end,
centriole
replication is
completed
Mitosis: Reproduction of DNA
• nuclear division for all somatic or body cells
• diploid cells (2N) result in making 2 diploid daughter
cells (2N).
• Four stages
–
–
–
–
Prophase
Metaphase
Anaphase
Telophase
Prophase = puddle of DNA
• “before-phase”
• chromatin shorten into
chromosomes
• centrioles move to opposite
ends, spindle fibers form
• nuclear envelope and nucleolus
disappear
Metaphase: Middle
• “middle-phase”
• chromosomes line up
on equatorial plate
• centromeres attach to
fibers
Anaphase: Apart
• “apart phase”
• chromosomes split
and chromatid is
pulled to opposite
centrioles
• spindle fibers shorten
Telophase: Tearing
• “end phase”
• chromosomes elongate to
chromatin
• nuclear envelope and
nucleolus reappear
• Cytokinesis: allows cell
membrane to pinch in to
separate 2 new daughter cells
– Separate from Telophase
Cell Division
• Mitosis: division of the nucleus
• Cytokinesis: division of the cytoplasm
• The amount of nutrients a growing cell requires
is directly related to its volume
Regulators of Cell Division
1. Chemical signals ( growth factors, hormones)
released by other cells
2. Availability of space: Normal cells stop
proliferating when they begin touching (
contact inhibition)
3. Cyclins and Cdks: proteins that allow the cell
to enter S phase
Meiosis: Reproduction of Sex Cells
A. Provides genetic variation in offspring
because daughter cells are haploid (1N),
where parent cells were diploid (2N).
B. Chromosomes exist in pairs called
homologous pairs; one from each parent.
1. Two kinds of chromosomes:
1. *autosomes- #s 1-22; determine body
characteristics
2. *sex chromosomes- #23; determine if male
(XY) or female (XX)
2. Somatic cells contain the diploid number of
chromosomes, 2N = 46 for humans.
3. Gametes contain the haploid number of
chromosomes, which is ½ the diploid number, 1N
= 23 for humans.
Meiosis I – reduction of chromosomes
4 phases1. Prophase I- homologous chromosomes pair up,
called tetrads; crossing-over?
2. Metaphase I- homologous pairs line up on equatorial
plate
3. Anaphase I- homologous pairs split, each
chromosome moves to opposite centrioles
4. Telophase I – cytokinesis occurs to separate into 2
daughter cells
Meiosis II
• division of chromosomes, similar to mitosis
except the 4 phases are II.
Result  4 haploids cells (1N).
In male, generate 4 sperm. In female, generate 1 large
egg
Diploid Cells (2N)  Meiosis  Haploid Cells (1N) 
Fertilization of 1N Egg + 1N Sperm = 2N Zygote
Three sources of genetic
variability:
1. Independent assortment of homologuescombination of maternal and paternal
chromosomes in gametes is 2 23 or 8
million.
2. Crossing over- genes on other
chromosomes can stick
3. Random fertilization – which sperm wins?