Cellular Transport & the Cell Cycle Chapter 8 Cellular Transport & the Cell Cycle

8.1 Cellular Transport-Osmosis Diffusion- the movement of particles from an area of higher concentration to an area of lower concentration (review) Osmosis-the diffusion of water across a selectively permeable membrane The water will move from the area of higher water concentration to an area of lower water concentration The difference in concentrations across the semi-permeable membrane is called a concentration gradient

8.1 Osmosis & Solution Types Isotonic Solution- a solution in which the concentration of dissolved substances outside the cell is the same as the concentration of the dissolved substances in the cell Hypotonic solution- a solution in which the concentration of dissolved substances outside the cell is lower than the concentration of the dissolved substances in the cell Hypertonic Solution- a solution in which the concentration of dissolved substances outside the cell is higher than the concentration of the dissolved substances in the cell

8.1 Cell Response The cell will respond differently depending on the type of solution it is in: In an isotonic solution, there will be no visible changes because water is moving in both directions across the membrane at the same rate In a hypotonic solution, the water will move into the cell, causing the cell to increase in size In a hypertonic solution, the water will move out of the cell, causing the cell to decrease in size

8.1 Passive Transport Passive transport is the movement of substances across the cell membrane without the use of energy Water moving across the plasma membrane is considered to be simple diffusion and is classified as passive transport In facilitated diffusion, carrier or channel proteins move substances across the membrane with the concentration gradient and is also considered passive transport

8.1 Active Transport Active transport is the movement of materials across a membrane that requires energy Carrier proteins that move substances across a membrane against the concentration gradient are exhibiting active transport In this process, carrier proteins bind to the substance, then change shape in order to release the substance on the other side, before returning to their original shape.

8.1 Transport of Large Particles Cells can also absorb or release substances without using the plasma membrane to do so: Both are considered to be active transport, as they require energy Endocytosis: a process by which a cell surrounds and takes in a material from its environment Exocytosis: a process by which materials are expelled or secreted from a cell

8.2 Cell Growth & Reproduction Most cells are between 2 and 200 micrometers (1 micrometer = 1 millionth of a meter) Cell efficiency is related to cell size Larger cells are less efficient This is because they have a smaller surface area to volume ratio Smaller cells are more efficient This is because they have a larger surface area to volume ratio

8.2 Cell Size The amount of DNA can limit the size of a cell If there is not enough DNA to support the needs of the cell, the cell does not grow As a cell gets bigger, the plasma membrane has to move exponentially increasing amounts of substances into and out of the cell Eventually, the plasma membrane won’t be able to keep up

8.2 Cell Division Cells will divide before they get too big in order to prevent the problems associated with being too big Cell division is the process by which new cells are produced from one cell It results in 2 cells that are identical to the first cell Cell division must take place in order to replace the cells that are dying

8.2 Chromosomes Chromosomes were first observed as short, stringy structures that appeared suddenly and vanished right after cell division These structures contain DNA, which is copied and passed from generation to generation Most of the time, they are chromatin, strands of DNA wrapped around histones, a type of protein The chromatin must organize before cell division can occur

8.2 The Cell Cycle The cell cycle is the sequence of growth and division of a cell There are 2 general phases in the cell cycle Interphase- when a cell grows and carries on metabolism Interphase occurs during most of a cell’s lifespan Mitosis- cell division when 2 daughter cells are formed The cytoplasm divides after mitosis to separate the 2 new cells

8.2 Interphase Interphase is divided into 3 parts: The cell grows rapidly and produces lots of protein The cell copies its chromosomes (DNA synthesis & replication) The cell manufactures organelles, and Centrioles replicate

8.2 Mitosis When cells reach their maximum size, they undergo mitosis Mitosis has 4 phases: Prophase Metaphase Anaphase Telophase

8.2 Prophase Prophase is the 1st phase of mitosis (and the longest) In prophase: The chromatin coils into chromosomes, which have 2 halves, called sister chromatids, held together by a centromere Sister chromatids contain 2 exact copies of the DNA The nucleus, nucleolus, and nuclear envelope begin to disappear By the end of prophase, they are gone In animal cells: centrioles move to opposite ends of the cell and the spindle forms between them In plant cells: the spindle forms without the presence of centrioles

8.2 Metaphase Metaphase is the 2nd phase of mitosis In metaphase: The doubled chromosomes attach to the spindle fibers by the centromeres The chromosomes line up at the middle of the spindle with one sister chromatid pointing to each side of the cell

8.2 Anaphase Anaphase is the 3rd phase of mitosis Anaphase starts with the separation of the sister chromatids In anaphase: The centromeres split apart and the chromatid pairs separate They are pulled apart due to the shortening of the microtubules in the spindle fibers

8.2 Telophase Telophase is the 4th phase of mitosis In telophase: It starts when the chromatids reach the opposite sides of the cell The chromosomes unwind The spindle disappears The nucleolus reappears and the nuclear envelope starts forming around each set of chromosomes A new membrane starts to form between the 2 new nuclei

8.2 Cytokinesis Following telophase, the cell undergoes cytokinesis, when the cell’s cytoplasm divides In plants: a cell plate forms in telophase and forms new cell walls In animals: the plasma membrane folds in to touch in the center

8.2 Results of Mitosis In unicellular organisms: after mitosis, they remain as single cells In multi-cellular organisms: after mitosis, cell growth and reproduction results in the specialization of cells to form tissues, which form organs, which work together to form organ systems, which are necessary for multi-cellular organisms

8.3 Regulating the Cell Cycle The cell cycle is regulated by a combination of enzymes, called cyclins, and proteins that are activated when they attach to the cyclin The cell cycle can run out of control if the body does not produce the right enzymes, produces too much or too little of a certain enzyme, or produces enzymes at the wrong time

8.3 Cancer Cancer is the result of uncontrolled cell division Scientists believe that one or more of the genes that produce the enzymes or proteins involved in the cell cycle changes This uncontrolled cell division usually starves surrounding cells of their nutrients While scientists can’t pinpoint a cause of cancer, it appears to be a combination of environmental and genetic factors They do agree, however that a diet low in fats and high in fiber can reduce the risk