Cell Reproduction/Cell Cycle

DNA

• DNA deoxyribonucleic acid– a long, thin molecule that contains info to run cell

• DNA is organized into genes• Genes is a segment of DNA that contains

information; passed from parent to offspring– Genes code for proteins• Proteins determine traits

Chromosomes• Chromosome a rod-shaped

structure that forms when a single DNA molecule is coiled tightly before cell division.

• Chromatid a copy of a chromosome

• Centromere protein disk that attaches two chromatids around the middle.

Chromosomes

• The DNA in eukaryotic cells wraps around proteins called histones. – They aid in shaping and maintaining the tight

packing of DNA

I. Prokaryotic Cell Cycle

A. Bacterial cells contain single, simple, circular strands of “naked” DNA.

B. Binary Fission- asexual reproduction of prokaryotic cells.1. Cells replicate DNA2. DNA copies attach to opposite sides of the cell membrane3. Cell membrane pinches in creating 2 identical cells.

Binary Fission

II. Eukaryotic Cell Cycle

Life cycle of a cell that begins when a cell is formed and ends when it divides.

G1 growth phase of the cell-cell grows and carries out major functions of cell-majority of cell life.

S When the DNA is copied-G2 Mitochondria and other organelles replicate-prepare

for nuclear divisionM Mitosis occurs-nucleus of cell divides into two nucleiC cytoplasm divides-called cytokinesis

HW Question

• In binary fission, how does the offspring’s genetic code compare to the parent’s? Explain.

• Using your knowledge of prokaryotic and eukaryotic cells, why do you think the eukaryotic cell cycle is longer/has more steps than the prokaryotic cell cycle?

A. Interphase – normal growth phase of the cell.- the majority of the cell cycle is spent in interphase1. G1 phase- growth of the cell immediately following cell division2. S phase- DNA replication3. G2 phase- final preparations for mitosis

• Cells that don’t reproduce don’t have an S or G2 phase. (ex. Red blood cells)

• Genetic material is in loose tangles of DNA and associated proteins (Histones) called Chromatin.

• Chromatin is invisible to most light microscopes.

B. Mitosis- the production of 2 new, identical nuclei.1. Prophase (pairing)

a. Chromatin coils to form thick, compact structures called Chromosomes.

b. Each chromosome is composed of two identical copies of DNA (Sister Chromatids) held together by a centromere.

c. Nuclear membrane and nucleolus begin to breakdown.

d. Centrioles (bundles of microtubules) begin to migrate to opposite poles of the cell.

e. Long microtubules called Spindle fibers extend from the centrioles across the cell

Chromosome

Prophase

2. Metaphase (midline)a. Spindles fully form and attach to the centromeres of each chromosome.b. Chromosomes are pulled to the equator of the cell forming a line.

3. Anaphase (away)a. Centromeres are split and sister chromatids are pulled towards opposite poles of the cell.

** At this point each chromatid is now called a Chromosome.

4. Telophase (two nuclei)a. Identical chromosomes sets reach opposite poles of the cell.b. Spindle fibers break down.c. Two new nuclear membranes begin to form around the chromosome sets.d. Chromosomes begin to uncoil into chromatin.

** This ends mitosis, but not the cell cycle.

Telophase

C. Cytokinesis- the splitting of the cytoplasm into two identical daughter cells.- In animal cells, the cell membrane is pinched in by constricting microtubules creating a cleavage furrow.- In plant cells, secretion vesicles form a cell plate between the chromosome sets splitting the cell membrane and cell wall.- Can begin as early as Anaphase- Each new cell immediately begins the G1

phase of Interphase.

Plant cell mitosis

Animal cell mitosis

Mitosis Rap

• https://www.youtube.com/watch?v=pOsAbTi9tHw

III. Meiosis- production of haploid gametes (sex cells)

A. Homologous chromosomes- matching pairs of chromosomes that are the same size, shape and code for the same hereditary traits, but are not genetically identical.

Chromosome numbers

• Sex chromosomes – are chromosomes that determine the sex of an organism.– XX – female (mom gives X, dad gives X)– XY – male (mom gives X, dad gives Y)

• Autosomes – All the other chromosomes other than the sex chromosomes (humans have 22 pairs).

1. Diploid cells- contain a full set of homologous pairs ( 1 set of maternal and 1 set of paternal chromosomes).

a. Diploid # (2n) is the total # of chromosomes in a normal body cell.

ex. Human diploid # is 46; Chimps is 48

2. Haploid cells- contain a half set of homologous pairs or 1 of each homologous pair.

a. Haploid # (n) is half of the diploid #.ex. Human haploid # is 23; chimps is 24b. Gametes (sex cells) are haploid.- male sperm- female egg- fusion of egg and sperm produces a

diploid (2n) cell called a zygote

B. Meiosis I*All DNA is replicated1. Prophase I

a. Chromatin coils to form chromosomes.b. Nucleus disappearsc. Homologous chromosomes pair up to form

tetrads.d. The chromatid arms of the homologous

pairs can become intermingled and exchange genetic material. (Crossing Over)

e. The random exchange of genes caused by crossing over creates chromosomes w/ a unique combination of genes. (Genetic Recombination)

2. Metaphase Ia. Homologous pairs of

chromosomes line up at the equator of the cell.

b. Spindle fibers attach to the centromeres.

3. Anaphase Ia. Homologous chromosomes are

randomly separated from each other and pulled to opposite sides of the cell. (Independent Assortment)

- Centromeres are not divided, sister chromatids remain attached

- Chromosome number is reduced from diploid(2n) to haploid(n).

4. Telophase I/ Cytokinesisa. New nuclei may form.b. Cell splits into two haploid cells (not

genetically identical).

C. Meiosis II1. Similar steps to mitosis, but w/ haploid cells.2. Sister chromatids are separated during Anaphase II.3. Telophase/ Cytokinesis produces 4 genetically diverse, haploid gametes.4. Males produce 4 functional sperm.5. In most female organisms, 1 large gamete (egg) and 3 smaller non-functional gametes (polar bodies) are produced.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html

Questions

• What are the differences between mitosis and meiosis? (Overall and in each phase)