Unit 1 Chapter 3 Cells

Cell Membrane: (plasma membrane)

The cell membrane regulates the movement of substances in and out of the cell, participates in signal transduction, and helps cells adhere to other cells. -The cell membrane is extremely thin, flexible, and selectively permeable. -It has a complex surface with adaptations to increase surface area

Cilia and flagella

are motile extensions from the cell; shorter cilia are abundant on the free surfaces of certain epithelial cells and move in a wave (respiratory linings, for example), and a lengthy flagellum can be found on sperm cells.

Lysosomes

are the "garbage disposals" of the cell and contain digestive enzymes to break up old cell components, bacteria, nutrient molecules, cholesterol, toxins, and drugs.

Mitochondria

are the powerhouses of the cell and contain enzymes needed for cellular respiration. 1) The inner membrane of the mitochondrion is folded into cristae which hold the enzymes needed in energy transformations to make ATP. 2) Very active cells contain thousands of mitochondria. 3) Mitochondria have their own DNA and reproduce by dividing.

endocytosis

molecules that are too large to be transported by other means are conveyed inside a vesicle that forms from a section of the cell membrane

Types of osmotic Solutions

-A solution with the same osmotic pressure as body fluids is called isotonic; 0.9% NaCl solution is isotonic to human cells -one with higher osmotic pressure than body fluids is hypertonic -One with lower osmotic pressure is hypotonic.

Filtration

-Because of hydrostatic pressure, molecules can be forced through membranes by the process of filtration. -Blood pressure is a type of hydrostatic pressure. -Particles are generally limited in movement by their size.

Diffusion (passive Mechanism)

-Caused by the random motion of particles and involves the movement of particles from an area of greater concentration to one of lesser concentration until diffusional equilibrium is reached (down a concentration gradient). -At equilibrium, particles continue to move but there is no net change in concentration. -Diffusion enables oxygen and carbon dioxide molecules to be exchanged between the air and the blood in the lungs, and between blood and tissue cells

Cell Membrane Structure

-The basic framework of the cell membrane consists of a double layer (bilayer) of phospholipids, with fatty acid tails turned inward and the water-soluble heads toward the surfaces. -The phospholipids can move, forming a stable fluid film. -Molecules that are soluble in lipids (gases, steroid hormones) can pass through the lipid portion of the membrane, while it is impermeable to water-soluble molecules -Embedded cholesterol molecules strengthen the membrane and help make the membrane less permeable to water-soluble substances. -Many types of proteins are found in the cell membrane, including integral, transmembrane, and peripheral membrane proteins. 1) Membrane proteins perform a variety of functions and vary in shape. 2) Some proteins function as receptors on the cell surface, starting signal transduction. 3) Other proteins aid the passage of molecules and ions as transport molecules or channels. 4) Proteins that protrude into the cell will anchor supportive rods and tubules (cytoskeleton). 5) Other proteins have carbohydrates attached (glycoproteins) and are used for cell identification. 6) Membrane proteins called cellular adhesion molecules (CAMs) help determine one cell's interactions with other cells.

Cells

-The human body consists of 75 trillion cells that vary considerably in shape and size yet have much in common. -Differences in cell shape make different functions possible. -A cell continually carries out activities essential for life, as well as specialized functions, and adapts to changing conditions. -Genes control a cell's actions and responses.

Osmosis

-is a special case of diffusion in which water moves from an area of greater water concentration (where there is less osmotic pressure and fewer solutes) across a selectively permeable membrane to an area of lower water concentration (where there is greater osmotic pressure and more solutes). -The membrane is soluble to water but insoluble to the solutes. -Osmotic pressure is the pressure needed to lift a volume of water; more impermeable solutes creates more pressure.

Facilitated diffusion

-uses membrane proteins that function as carriers to move molecules (such as glucose and amino acids) across the cell membrane. -The number of carrier molecules in the cell membrane limits the rate of this process.

Three various forms of endocytosis

1) Pinocytosis is in which cells engulf liquids; cell drinking 2) Phagocytosis is in which the cell takes in larger particles, such as when a white blood cell engulfs a bacterium; cell eating -Once the vesicle enters the cell, it will combine with a lysosome and the contents will be digested by lysosomal enzymes. 3) Receptor-mediated endocytosis allows the cell to take in very specific molecules (ligands) that pair up with specific receptors on the cell surface.

Movement through cell membranes

1) The cell membrane is a selectively permeable membrane so it controls what passes through it. 2) Mechanisms of movement across the membrane may be passive, requiring no energy from the cell (diffusion, facilitated diffusion, osmosis, and filtration) or active mechanisms, requiring cellular energy (active transport, endocytosis, and exocytosis).

Cell Nucleus

1) The fairly large nucleus is bounded by a double-layered nuclear envelope containing relatively large nuclear pores that allow the passage of certain substances. 2) Contains a fluid called nucleoplasm 3) The nucleolus is composed of RNA and protein and is the site of ribosome production. 4) Chromatin consists of loosely coiled fibers of protein and DNA. Condensed DNA is referred to as chromosomes.

Composite Cell

A cell consists of three main parts the nucleus, the cytoplasm, and the cell membrane. (Within the cytoplasm are specialized organelles (little organs) that perform specific functions for the cell.)

Meiosis

Four cells (sperm or ova) are produced, each of which contains half of the parent cell's genetic information (gametogenesis).

Cytoplasm

The cytoplasm consists of a clear liquid (cytosol), a supportive cytoskeleton, and networks of membranes and organelles.

Cell Cycle

The series of changes a cell undergoes from the time it is formed until it reproduces -consists of interphase, mitosis, and cytokinesis. -is controlled by special protein checkpoints. Most cells do not divide continually. Cells have a maximum number of times they can divide because of built-in "clocks" (telomeres) on the tips of chromosomes. - Restriction checkpoint - the spot where a cell would continue in the cell cycle and divide, move into a non-dividing stage, or die.

Microfilaments and microtubules

are thin, threadlike structures that serve as the cytoskeleton of the cell. 1) Microfilaments, made of actin, cause various cellular movements; they group together to form myofibrils in muscle. 2) Microtubules, made of the globular protein tubulin, are attached in a spiral to form a long tube; important in cell division 3) Intermediate fibers, made of different proteins in different cells, are abundant in skin cells and neurons.

The centrosome

centrosome is a structure made up of two hollow cylinders called centrioles that function in the separation of chromosomes during cell division; made of nine groups of three microtubules.

Peroxisomes

contain enzymes that function in the breakdown of lipids and hydrogen peroxide, and detoxification of alcohol.

Vesicles

form from part of the cell membrane or the Golgi apparatus and store or transport materials.

Mitosis

is a carefully orchestrated division of the nucleus of the cell that results in each of two daughter cell receiving an exact copy of the mother cell's genetic material

Interphase

is a period of great metabolic activity in which the cell grows and synthesizes new molecules and organelles. 2) During the G1 and G2 phases of interphase, the cell grows and other structures are duplicated. 3) During the S phase of interphase, the DNA of the cell is replicated in preparation for cell division.

The Golgi apparatus

is composed of flattened sacs, and refines, packages, and transports proteins formed in the rough ER. 1) Vesicles formed in the ER travel to the Golgi apparatus which modifies their contents by adding sugar molecules to the proteins to stabilize their structure or to enable folding. 2) A new vesicle pinches off the Golgi apparatus and may then move to the cell membrane and secrete its contents to the outside (exocytosis).

Endoplasmic reticulum (ER)

is made up of membranes, flattened sacs, and vesicles, and provides a tubular transport system inside the cell. 1) With ribosomes, endoplasmic reticulum (ER) is rough ER, and functions in protein synthesis and processing. 2) Without ribosomes, it is smooth ER, and functions in lipid synthesis, absorption of fats, and metabolism of drugs -Ribosomes are found with ER and are scattered throughout the cytoplasm. 1) They are composed of protein and RNA and provide a structural support and enzymatic activity for the RNA molecules that come together in protein synthesis. 2) Clusters of ribosomes in the cytoplasm are called polysomes.

Cytokinesis

is the division of the cytoplasm and organelles and occurs in both processes.

Exocytosis

is the movement of materials out of the cell in a vesicle that fuses with the cell membrane and opens up to the outside to secrete the material.

Active Transport (Active Mechanisms)

uses ATP to move molecules from areas of low concentration to areas of high concentration through carrier molecules in cell membranes. -May also be called pumps. -As much as 40% of a cell's energy supply may be used to fuel this process. -The union of the specific particle to be transported with its carrier protein triggers the release of cellular energy (ATP), which in turn alters the shape of the carrier protein, releasing the particle to the other side of the membrane. -Particles that are actively transported include sugars, amino acids, and sodium, potassium, calcium, and hydrogen ions, as well as nutrient molecules in the intestines.