Chapter 5: Cell Growth and Division

5.1 Cell Cycle The Cell Cycle has four main stages  What is the cell cycle? Cell Cycle is the regular pattern of growth, DNA duplication and cell division.

Gap 1 (G1 Phase) During the Gap 1 phase, a cell carries out its normal functions. Cells increase in size and organelles increase in number There is a check point to move forward.

 Synthesis Phase (S Phase) The cell makes a copy of its own DNA

 Gap 2 (G2 Phase) Cells continue to carry out their normal functions and additional growth occurs. There is another checkpoint at the end of the cycle.

 Mitosis (M Phase) Mitosis – division of the cell nucleus and its contents. Nuclear membrane disappears, the duplicated DNA separates and two new nuclei form. Cytokinesis – process that divides the cell cytoplasm to produce 2 new daughter cells. Occurs in all body cells except the sex cells.

 Cells Divide At Different Rates Prokaryotic Cells – typically divide quicker because they are simpler than eukaryotic cells Cells that divide rarely go into G0 phase where they will continue to function but do not divide.

5.2 Mitosis and Cytokinesis Chromosomes condense at the start of mitosis.  How many nucleotides make up DNA? DNA is made up of four nucleotides.  What is a chromosome? A chromosome is one long continuous thread of DNA that consists of numerous genes along with regulatory information. Your body cells have 46 chromosomes.

Design of a Chromosome During mitosis DNA is condensed so that it can be properly separated.  What are histones? DNA wraps around histones which are a group of proteins.  What is chromatin? Chromatin is the loose combination of histones and DNA.

Chromatid are formed when chromatin is supercoiled and forms the X shaped chromosome. Chromatid is half of a chromosome.  What are centromeres? Centromeres hold together the two chromatids.  What are telomeres? At the end of the chromatids are telomeres which are repeating nucleotides that do not form genes.

 Interphase Interphase includes the G1, S and G2 phase of the cell cycle. At the end of the G2 phase an individual cell has two full sets of DNA (or chromosomes) and is large enough to divide.

 What are the four phases of mitosis? Prophase Metaphase Anaphase Telophase

 Prophase Chromatin condenses into tightly coiled chromosomes. Nuclear membrane disappears, centrioles move to the opposite sides and spindle fibers form.

 Metaphase Spindle fibers attach to each chromosomes. The chromosomes line up in the middle of the cell.

 Anaphase Chromatids separate to opposite sides of the pole.

 Telophase A complete set of chromosomes are positioned at each pole of the cell. The nuclear membrane reforms and chromosomes begin to unwind.

 Cytokinesis Divides the cytoplasm into two cells and completes a full stage of the cell cycle. In animal cells, the membrane forms a furrow and is pulled inward. In plant cells, a cell plate forms between the two nuclei and then a new cell wall grows.

5.4 Asexual Reproduction Binary fission is similar in function to mitosis.  What is sexual reproduction? Sexual reproduction – the joining of the gametes from two different parents.  What is asexual reproduction? Asexual reproduction – the creation of offspring from one parent and does not involve the joining of gametes.

 What is Binary Fission? Binary fission – is the asexual reproduction of a single-celled organism by division into two roughly equal parts. Advantages of asexual reproduction is that it is more efficient. Disadvantages is the possibility of a change in environment and there are no variations to survive.

 Other types of Asexual Reproduction Budding – a small projection grows on the surface of a parent organism Ex. Hydra and yeast Fragmentation – a parent organism splits into two pieces each which can grow into a new organism Some organisms reproduce sexually and asexually such as sea anemone.