Transcript Chapter 6 Chromosomes and Cell Reproduction

Chapter 6
Chromosomes and Cell Reproduction
Section 6-1
Cell division (cell reproduction)
•Occurs in humans and LT at diff times in their life
•Formation of gametes (egg/sperm) involves special types
of cell ÷ (this will be covered in chapter 7)
•When cells ÷, DNA is 1st copied and then ÷
Section 6-1
Prokaryotic (Bacteria) Cell Reproduction:
Binary fission:
•Form of asexual reproduction in bacteria cells that
produces identical offspring
•Binary fission occurs in 2 stages: 1st, DNA is copied, then
cell ÷, eventually the ÷ prokaryote is pinched into 2
independent cells
Section 6-1
Eukaryotic Cell Reproduction:
Gene: piece of DNA that codes for a protein or RNA
•As eukaryotic cell prepares to ÷, DNA and proteins
associated w/ DNA coil into chromosomes
Chromatids: 2 exact copies of DNA that make up each
chromo
Centromere: where 2 chromatids of chromo are attached
Section 6-1
•Homologous chromosomes: chromo similar in size,
shape, genetic content
•Each homologue in a pair of homologous chromosomes
comes from 1 of the 2 parents
•46 chromosomes in human somatic (body) cells are actually
two sets of 23 chromosomes (23 from mom, 23 from dad)
•Diploid: cell w/ 46 chromo (23 from mom, 23 from dad)
•Haploid: cell w/ only 23 chromo, such as gametes
•Zygote: fusion of 2 haploid gametes (fertilization) to form
1 diploid fertilized egg cell (mom’s 23 w/ dad’s 23 = 46)
Section 6-1
•Autosomes: chromo not directly involved in determining
sex (gender) of an individual; pairs #1-22
•Sex chromosomes: 1 pair of chromo in humans, contain
genes that determine sex of individual; pair #23 referred to
X and Y; XX = female, XY = male
Section 6-1
Change in Chromo #:
•Humans missing 1 of 46 chromosomes usually don’t survive
•Trisomy: more than 2 copies of a chromosome, will not
develop properly; 3 copies of #21= Down’s Syndrome
•Karyotype: photo of chromo in a dividing cell showing
chromo arranged by size
Section 6-1
Change in Chromo Structure:
• ∆ in organism’s chromo structure are mutations
• Breakage of chromo can lead to 4 types of mutations:
1. deletion mutation: piece missing
2. duplication mutation: piece added
3. inversion mutation: piece turned upside down
4. translocation mutation: piece from chromo is
put on a different chromo
Section 6-2
Cell Cycle:
•Repeating sequence of cellular growth/÷ during life of
organism
Interphase:
•1st 3 phases of cell cycle, 90% of cell’s time is in this phase
Section 6-2
5 Phases of Cell Cycle:
1. 1st growth (G1) phase: cell grows rapidly and carries
out routine functions
2. Synthesis (S) phase: DNA is copied
3. 2nd growth (G2) phase: preparations made for nucleus
to ÷
4. Mitosis: nucleus of cell ÷ into 2 nuclei
5. Cytokinesis: cytoplasm ÷
Section 6-2
Control of Cell Cycle:
•Checkpoints at which feedback signals from cell can trigger
or delay next phase of cell cycle
•1. Cell growth (G1) checkpoint makes decision of
whether cell will ÷
•2. DNA synthesis (G2) checkpoint DNA replication is
checked by DNA repair enzymes
•3. Mitosis checkpoint triggers exit from mitosis
Section 6-2
When Control Is Lost: Cancer!
•If a gene that controls cell growth/÷ is mutated, then
regulation of cell growth/÷ can be disrupted = cancer and
uncontrolled cell growth results!
Bladder cancer
Section 6-3
Mitosis - Division of the Nucleus in 4 phases:
•1. Prophase: Nuclear envelope dissolves; spindle forms
•2. Metaphase: Chromo move to center and line up along
the equator
•3. Anaphase: Centromeres ÷; chromo move to opposite
ends of cell
• 4. Telophase: Nuclear envelope forms around chromo at
each pole; Mitosis is complete
Section 6-3
Cytokinesis – Division of the Cytoplasm:
• As mitosis ends, cytokinesis begins
• Cytoplasm of cell ÷ in 1/2, cell membrane grows to
enclose each new cell, forming 2 separate genetically
identical cells from 1 cell