Chapter 6Chromosomes and Cell

Reproduction

Section 6-1Cell 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 6-1Prokaryotic (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 6-1Eukaryotic 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 chromosomesChromatids: 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

missing2. duplication mutation: piece

added3. inversion mutation: piece

turned upside down4. translocation mutation: piece

from chromo is put on a different chromo

Section 6-2Cell Cycle:•Repeating sequence of cellular growth/÷ during life of organismInterphase: •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 functions2. Synthesis (S) phase: DNA is copied 3. 2nd growth (G2) phase: preparations made for nucleus to ÷4. Mitosis: nucleus of cell ÷ into 2 nuclei5. Cytokinesis: cytoplasm ÷

Section 6-2Control 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 6-3Mitosis - 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