Cellular Transport and the Cell Cycle Chapter 8

Cellular Transport and the Cell Cycle Chapter 8

Chapter 8 Sections ► 8. 1 Cellular Transport § Osmosis § Passive Transport § Active Transport ► 8. 2 Cell Growth and Reproduction § Cell Size limitations § Cell Reproduction § Cell Cycle ► 8. 3 Control of the Cell Cycle § Normal § Cancer

Cellular Transport Section 8. 1

Cellular Transport ► Substances two ways: move into and out of the cell in 1. ) Passive Transport – No energy is used. ►Diffusion ►Osmosis ►Facilitated Diffusion 2. ) Active Transport – Energy is used. ►Endocytosis ►Exocytosis

► Diffusion is the movement of molecules from high to low concentrations. § Diffusion continues until dynamic equilibrium is reached (the same concentration throughout). ► Osmosis – diffusion of water across a cell membrane § The cell membrane does NOT limit water movement. Water crosses the membrane freely. § It stops molecules that are dissolved in water from entering the cell.

Osmosis ► What determines whether water flows into or out of a cell? § The amount of dissolved substances inside the cell compared to outside the cell. ► Isotonic Environment ► Hypertonic Environment § Amount of substances outside the cell is the same as inside cell. § Water flows into and out of the cell at the same rate. § Amount of substances outside the cell is less than inside the cell. § Water flows into cell. § Amount of substances outside the cell is more than inside the cell. § Water flows out of cell.

Facilitated Diffusion Facilitated diffusion § Diffusion of substances into or out of the cell with the help of transport proteins. § Substances move from high to low concentrations during facilitated diffusion. § There are two types of transport proteins: ► Channel proteins ► Carrier Proteins

Active Transport ► Active Transport – Movement of substances across the cell membrane from areas of lower to higher concentration § Active transport requires energy! ► The substances move across the cell membrane against the concentration gradient (from low to high concentration) § This is the opposite of diffusion (passive transport) ► Like facilitated diffusion (a type of passive transport), active transport occurs with the help of carrier proteins.

Channel and Carrier Proteins

Transport of Large Substances ► Sometimes substances are too large to cross the cell membrane or move through a transport protein. ► Endocytosis § Cell surrounds and takes in material that is too large for transport through the membrane ► Exocytosis § Expulsion or secretion of materials § The opposite of endocytosis ► Both endocytosis and exocytosis require energy. § Are they types of passive or active transport?

Classwork ► Section Assessment page 200 (1 -4)

Section 8. 2 Cell Growth and Reproduction

Cell Size Limitations ► Why are cells so small? ► Cell size is limited by 3 things: ► Diffusion Limits cell size ► DNA Limits cell size ► Surface area to volume ratio limits cell size § It would be very difficult to get things into and out of the cell because diffusion is slow and inefficient over large areas § It would take too long to construct the # of proteins necessary to support a large cell because there is a limit to how quickly DNA can be copied and read § Volume increases faster than surface area ► (it gets bigger inside than it does outside) § It would require more nutrients, and have to get rid of more wastes, but through a smaller surface area (cell membrane)

Cell Division ► All cells come from other cells. (Schleiden and Schwann - Cell Theory)

Cells divide to maintain their sizes ► Cells cannot become too large, so they divide to form more cells……. they reproduce. ► When organisms grow, new cells are made. ► When cells are damaged or die, they are replaced by new cells. ► The process of cell reproduction is called cell division.

Chromosomes ► Chromosomes can only be seen just before a cell divides and they disappear after it divides. ► Chromosomes are tightly wound DNA molecules. § (They normally exist as chromatin) ► Chromosomes (DNA) are copied during cell division and are passed on from one generation of cells to the next.

► Chromatin- long strands of DNA ► Before division, the long strands must be reorganized and recoiled ► The chromatin becomes tightly packed

The Cell Cycle ► Is the sequence of growth and division of a cell

The Cell Cycle ► There are two primary parts of the cell cycle. ► The first part is called interphase. § Cells spend most of their lifetime in this phase growing and metabolizing. § Chromosomes are duplicated ► The second part is called mitosis. § Mitosis is a very short compared to interphase. § Where division occurs- 2 daughter cells formed § Each containing a complete set of chromosomes

The Cell Cycle ► G 1 ►S INTERPHASE ► G 2 ► PROPHASE ► METAPHASE ► ANAPHASE ► TELOPHASE ► CYTOKENISIS MITOSIS

The Cell Cycle ► Interphase is divided into three parts. ► G 1 –Rapid Growth. Protein production is high. Chromosome not visible. ► S – DNA copied. ► G 2 –Organelles produced. the cell goes into mitosis (cell division) Plant Cell ► Then Animal Cell

► Steps of mitosis: 1 - Prophase: Chromosomes form

Prophase ► Chromatin coils up and becomes the visible chromosomes. ► Chromosomes consist of two halves (which are copies of one another) called sister chromatids. ► A structure called a centromere holds the sister chromatids together. ► The nucleus of the cell disappears. ► Centrioles migrate to opposite poles (they help pull the chromatids apart when the cell divides). ► Spindle fibers made of microtubules form between centrioles (help pull sisters apart too).

2 - Metaphase: Metaphase Chromosomes line up

Metaphase ► Chromosomes become attached to spindle fibers at centromeres. ► Chromosomes are pulled to middle of cell (equator) by spindle fibers. They all line up. ► Each sister chromatid is attached to its own spindle fiber which is connected to the opposite pole of the cell.

3 - Anaphase: Chromosomes begin to be pulled apart by spindle fibers.

4 - Telophase: Sister chromatids reach opposite ends of the cell

Telophase ► The is the reverse of Prophase. cells nucleus reforms. ► Chromosomes ► Spindle ►A unwind into Chromatin. breaks down. new nuclear envelope is formed around each set of chromosomes.

5 - Cytokenisis: Cytokenisis Cell splits into two cells. The plasma membrane is pinched into two parts to form the new animal cells Plants- cell plate is laid down along the equator

The Cell Cycle ► G 1 ►S INTERPHASE ► G 2 ► PROPHASE ► METAPHASE ► ANAPHASE ► TELOPHASE ► CYTOKENISIS MITOSIS

Results ► Daughter cells carry out the same cellular processes and functions as the parent cell ► Will grow and divide like parent

Levels of Organization

Section 8. 3 Control of the Cell Cycle

Control of the Cell Cycle ► Proteins called Cyclins and enzymes that attach to the cyclins control the timing of the cell cycle. § They are in charge of the cell cycle. ► Sometimes there is a failure in protein and enzyme production and cancer results. ► Cancer ► There is uncontrolled cell division. are many different possible causes of cancer including environmental factors and viral infections.

► Enzyme production is directed by genes located on chromosomes ► Genes are segments of DNA that controls the enzyme production

Cancer ► Cancerous cells form masses of tissue called tumors. § Tumors deprive normal cells of nutrients. ► Cancer can affect any tissue in the body. ► 2 nd leading cause of death in US.

Cancer Prevention ► Diets low in fat and high in fiber content. ► Vitamins cancer. ► Daily and minerals may also prevent exercise and control of environmental conditions.