Cell Structure and Function Plasma Membrane Cell Membrane

Cell Structure and Function

Plasma Membrane (Cell Membrane) • Contains cell contents • Double layer of phospholipids & proteins regulates the passage or transport of certain molecules into and out of the cell, while preventing the passage of others. • Called Semi-permeable

Phospholipids • Polar – Hydrophylic head – Hydrophobic tail • Interacts with water

Nucleus • Control center of cell • Double membrane • Contains – Chromosomes – Nucleolus

DNA • Hereditary material • Chromosomes – DNA – Protiens – Form for cell division • Chromatin

Nuclear Envelope • Separates nucleus from rest of cell • Double membrane • Has pores

Nucleolus • Most cells have 2 or more • Directs synthesis of RNA • Forms ribosomes

Cytoplasm • Viscous fluid containing organelles • components of cytoplasm – – Interconnected filaments & fibers Fluid = cytosol Organelles (not nucleus) storage substances

Centrioles • Pairs of microtubular structures • Play a role in cell division

Endoplasmic Reticulum • Helps move substances within cells • Network of interconnected membranes • Two types – Rough endoplasmic reticulum – Smooth endoplasmic reticulum

Rough Endoplasmic Reticulum • Ribosomes attached to surface – Manufacture protiens – Not all ribosomes attached to rough ER • May modify proteins from ribosomes

Smooth Endoplasmic Reticulum • No attached ribosomes • Has enzymes that help build molecules – Carbohydrates – Lipids

Mitochondria • Have their own DNA • Bound by double membrane

Mitochondria • Break down fuel molecules (cellular respiration) – Glucose – Fatty acids • Release energy – ATP

Golgi Apparatus • Involved in synthesis of plant cell wall • Packaging & shipping station of cell

Golgi Apparatus Function 1. Molecules come in vesicles 2. Vesicles fuse with Golgi membrane 3. Molecules may be modified by Golgi

Golgi Apparatus Function (Continued) 4. Molecules pinched-off in separate vesicle 5. Vesicle leaves Golgi apparatus 6. Vesicles may combine with plasma membrane to secrete contents

Lysosomes • Contain digestive enzymes • Functions – Aid in cell renewal – Break down old cell parts – Digests invaders

Cytoskeleton • Filaments & fibers • Made of 3 fiber types – Microfilaments – Microtubules – Intermediate filaments • 3 functions: – mechanical support – anchor organelles – help move substances

Pinocytic Vesicles • Also called cell drinking • Large pocket where large molecules such as proteins and lipids, which cannot pass through the cell membrane, will enter the cell • The edges close and pinch away forming a bubble or vacuole in the cytoplasm.

Meiosis • The process of cell division of the sex cell or gamete • When fertilization occurs, the two sex cells combine to form a simple cell called a zygote

Mitosis • Divides into two distinct process – Division of the nucleus – Division of the cytoplasm • Its an orderly series of steps by which the DNA in the nucleus of the cell is equally distributed to two daughter or identical nuclei • Not all cells reproduce at the same rate: – Blood forming cells in the bone marrow, cells of the skin, cells of the intestinal tract reproduce continuously. – Muscle cells reproduce every few years.

Interphase • “Resting Stage” • An exact duplicate of each nuclear chromosome is made (replication) • At the start of mitosis, each chromosome has already replicated and called a chromatid – Joined by a structure called a centromere • Two Centrioles are found in the Centrosome and they replicate in preparation for next step

Prophase • Two pairs of Centrioles start to separate toward the opposite ends or poles of the cell – Microtubules form between them – Nuclear membrane starts to dissolve – Nucleolus disappears – DNA becomes highly coiled

Metaphase • Nuclear membranes completely dissolves • Chromatid arrange themselves in a single file – Equatorial plate

Anaphase • Chromatid pairs separate and pulled by the spindle fiber toward the Centrioles • Two chromatids or each replicated chromosome are now fully separated

Telophase • Chromosomes migrate to the opposite poles of the cell – They start to uncoil to become loosely arranged chromatin granules • Nuclear membrane and nucleolus reappear to help reestablish the nucleus as the definite organelle – Two new daughter cells are formed

Molecule Movement & Cells • Passive Transport • Active Transport • Endocytosis (phagocytosis & pinocytosis) • Exocytosis

Passive Transport • No energy required • Move due to gradient – differences in concentration, pressure, charge • Move to equalize gradient – High moves toward low

Types of Passive Transport 1. Diffusion 2. Osmosis 3. Facilitated diffusion

Diffusion • Molecules move to equalize concentration

Osmosis • Special form of diffusion • Fluid flows from lower solute concentration • Often involves movement of water – Into cell – Out of cell

Solution Differences & Cells • solvent + solute = solution • Hypotonic – Solutes in cell more than outside – Outside solvent will flow into cell • Isotonic – Solutes equal inside & out of cell • Hypertonic – Solutes greater outside cell – Fluid will flow out of cell

Facilitated Diffusion • Differentially permeable membrane • Channels (are specific) help molecule or ions enter or leave the cell • Channels usually are transport proteins (aquaporins facilitate the movement of water) • No energy is used

Process of Facilitated Transport • Protein binds with molecule • Shape of protein changes • Molecule moves across membrane

Active Transport • Molecular movement • Requires energy (against gradient) • Example is sodium-potassium pump

Endocytosis • Movement of large material – Particles – Organisms – Large molecules • Movement is into cells • Types of endocytosis – bulk-phase (nonspecific) – receptor-mediated (specific)

Process of Endocytosis • Plasma membrane surrounds material • Edges of membrane meet • Membranes fuse to form vesicle

Forms of Endocytosis • Phagocytosis – cell eating • Pinocytosis – cell drinking

Exocytosis • Reverse of endocytosis • Cell discharges material

Exocytosis • Vesicle moves to cell surface • Membrane of vesicle fuses • Materials expelled

Disorders of the cell structure • Cells may decrease in size- atrophy – Due to aging or disease • Cells may increase in size- hypertrophy – Caused by an increase in workload • Cells can increase in number- hyperplasia • Cells have the ability to change into another type of cell- metaplasia – A protective response to a stimulus such as smoking

Disorders of the cell structure (continued) • The change to the size, shape, and organization of cells as a result of a stimulus- dysplasia • Then progresses to Neoplasia – Change in the cell structure with an uncontrolled growth pattern

Trauma or Injury • Hypoxia- a decreased blood flow to cellular structures • Anoxia- a lack of oxygen flow to the cellular structures

Tumor • Results when cell division does not occur in the usual pattern – Also known as neoplasms • Can be divided into two groups: – Benign – Malignant

Benign • Composed of cells contained to the local area. – Other names: wart, papilloma • Most can be surgically removed

Malignant • Called cancer • Continue to grow, crowding out healthy cells, interfering with body functions and drawing nutrients away from the body tissue • Can spread through a process called metastasis

Symptoms of Cancer • • • Changes in bowel or bladder habits Sores that do not heal Obvious changes in mole or wart Unusual bleeding or discharge A new lump or thickening in the breast or elsewhere • Difficulty in swallowing or frequent indigestion • Persistent cough or hoarseness

How to detect • • X-ray Mammogram Sonogram Biopsy