Chapter 8 Biology CPA Thank you, Miss Colabelli! Cell Reproduction Chapter 8 Biology CPA Thank you, Miss Colabelli!

Chromosomes Rod shaped structures made of DNA and proteins Chromosomes are visible in cells undergoing division Chromosomes are made by DNA coiling into tight structures Consist of two identical halves

Chromosome Structure Histones are proteins that DNA wraps around to make the chromosome shape Chromosomes are made of two sister chromatids Identical to each other

Chromosome Structure Each chromosome is made of two “sister” chromatids Near center of the chromosome is the centromere Chromosomes are tightly coiled strings of DNA called chromatin

Chromosome Numbers There is a specific number of chromosomes in each organism Ex: Humans have 46, chimpanzees have 48 Humans have autosomes and sex chromosomes We have 2 sex chromosomes Either X or Y We also have 44 autosomes Which do not code for gender

Chromosome Numbers Every cell of an organism produced by sexual reproduction has two copies of each autosome One copy from mom and one copy from dad The two copies of each pair is called homologous chromosomes Same size and shape Carry genes for the same traits

Karyotype A karyotype is a picture of one set of chromosomes Shows you sex of organism Shows your any chromosomal disorders

Chromosome Numbers A diploid cell contains 2 sets of each chromosome Prefix di = 2 Abbreviated as 2n n = number of chromosomes A haploid cell contains only 1 set of each chromosome Half of the total number Usually sex cells

Cell Division in Prokaryotes No nucleus No organelles Ex: Bacteria Reproduction is very fast Copy DNA Split into two identical daughter cells Cell division is called binary fission

Cell Division in Eukaryotes Have a nucleus Have organelles Ex: Humans, plants Both nucleus and cytoplasm need to divide Process of making new cells is called mitosis Makes two identical daughter cells Complex reproduction Everything needs to be regulated! Much more complex process – about 18 hours!

Cell Division and Reproduction Asexual Reproduction Produces identical offspring from a single parent Used by many single-celled organisms Ex: bacteria Occurs very quickly Sexual Reproduction Produces genetically different offspring from two parents Fusion of two parent cells Creates haploid gametes (sex cells)

The cell Cycle A repeating set of events in the life of a cell A cell splits to make 2 identical copies This occurs in 3 main stages Interphase – growth Mitosis – division of the cell Cytokinesis – Splitting of the cytoplasm

Interphase Cell growth Majority of cell’s life span is spent in this phase 3 Part of Interphase: G1, S, G2

G1 Phase Gap 1 Phase The cell is growing to mature size

S Phase S = synthesis of DNA DNA is copied so there is a set for each new cell

G2 Phase Gap 2 Phase Cell grows again Replication of organelles Cell prepares for cell division

mitosis Cell Division

mitosis The part of a cell’s life cycle when the cell’s nucleus divides into 2 identical nuclei 4 steps: Prophase Metaphase Anaphase Telophase

Prophase Shortening and tight coiling of chromatin into chromosomes Nucleus breaks down and disappears Centrioles separate and move to opposite poles of the cell Centrosomes in plant cells Centrioles shoot off spindle fibers

metaphase Spindle fibers are connected to centromere of chromosomes Spindle fibers move chromosomes Chromosomes line up at the equator of the cell Chromosomes are in the MIDDLE

anaphase Sister chromatids attach to the short spindle fibers Chromatids of each chromosome separate at the centromere Chromosomes are pulled APART Spindle fibers shorten and bring the sister chromatids to opposite poles After chromatids separate, they are called individual chromosomes

Telophase Chromatids become chromatin Spindle fibers disassemble Nuclear envelope forms around each set of chromatin Nucleolus reappears

Cytokinesis Once mitosis has finished! Last stage of cell cycle Process is when the cytoplasm splits apart

Cytokinesis in Plant Cells A cell plate forms between the two nuclei The cytoplasm divides A cell wall forms two daughter cells

Cytokinesis in Animal Cells Cell membrane pinches in at equator Cleavage furrow

Cells in Various Stages of the Cell Cycle

Control of Cell Division Checkpoints (Regulatory Proteins) Repair enzymes fix any mutations G1 Checkpoint Proteins check to see if cell will be able to divide Check for cell size G2 Checkpoint DNA repair enzymes check results of DNA replication during S phase Mitosis checkpoint If all is correct, proteins will signal cell to exit mitosis Cell will renter interphase after cytokinesis and start process over again If a cell does not meet requirements for checkpoints, the cell will be programmed to die Apoptosis is controlled cell death

The Cell Cycle Clock: Cyclins and Cyclin-Dependent Kinases Two types of regulatory proteins are involved in cell cycle control: cyclins and cyclin-dependent kinases (Cdks) Cdks activity fluctuates during the cell cycle because it is controled by cyclins, so named because their concentrations vary with the cell cycle MPF (maturation-promoting factor) is a cyclin-Cdk complex that triggers a cell’s passage past the G2 checkpoint into the M phase

(b) Molecular mechanisms that help regulate the cell cycle Figure 12.17 M G1 S G2 M G1 S G2 M G1 MPF activity Cyclin concentration Time (a) Fluctuation of MPF activity and cyclin concentration during the cell cycle G1 S Cdk Figure 12.17 Molecular control of the cell cycle at the G2 checkpoint. Cyclin accumulation Degraded cyclin M G2 G2 checkpoint Cdk Cyclin is degraded Cyclin MPF (b) Molecular mechanisms that help regulate the cell cycle

Stop and Go Signs: Internal and External Signals at the Checkpoints An example of an internal signal is that kinetochores not attached to spindle microtubules send a molecular signal that delays anaphase Some external signals are growth factors, proteins released by certain cells that stimulate other cells to divide For example, platelet-derived growth factor (PDGF) stimulates the division of human fibroblast cells in culture

A clear example of external signals is density-dependent inhibition, in which crowded cells stop dividing Most animal cells also exhibit anchorage dependence, in which they must be attached to a substratum in order to divide Cancer cells exhibit neither density- dependent inhibition nor anchorage dependence

Density-dependent inhibition Figure 12.19 Anchorage dependence Density-dependent inhibition Density-dependent inhibition Figure 12.19 Density-dependent inhibition and anchorage dependence of cell division. 20 m 20 m (a) Normal mammalian cells (b) Cancer cells

Loss of Cell Cycle Controls in Cancer Cells Cancer cells do not respond normally to the body’s control mechanisms Cancer cells may not need growth factors to grow and divide They may make their own growth factor They may convey a growth factor’s signal without the presence of the growth factor They may have an abnormal cell cycle control system

A normal cell is converted to a cancerous cell by a process called transformation Cancer cells that are not eliminated by the immune system, form tumors, masses of abnormal cells within otherwise normal tissue If abnormal cells remain at the original site, the lump is called a benign tumor Malignant tumors invade surrounding tissues and can metastasize, exporting cancer cells to other parts of the body, where they may form additional tumors

A tumor grows from a single cancer cell. Figure 12.20 Lymph vessel Tumor Blood vessel Cancer cell Glandular tissue Metastatic tumor 1 A tumor grows from a single cancer cell. 2 Cancer cells invade neighboring tissue. 3 Cancer cells spread through lymph and blood vessels to other parts of the body. 4 Cancer cells may survive and establish a new tumor in another part of the body. Figure 12.20 The growth and metastasis of a malignant breast tumor.

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