Chapter 3 Cells Copyright  The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Introduction The basic organizational structure of the human body is the cell. There are about 75 trillion cells in the human body. Cell size is measured in micrometers. Differentiation is when cells specialize. As a result of differentiation, cells vary in size and shape due to their unique function.

A Composite Cell Also called a ‘typical’ cell Major parts include: Nucleus Cytoplasm Cell membrane Within the cytoplasm are specialized organelles that perform specific functions for the cell. Phospholipid bilayer Flagellum Nucleus Nuclear envelope Chromatin Nucleolus Ribosomes Microtubules Basal body Cell membrane Centrioles Rough Endoplasmic reticulum Mitochondrion Smooth Endoplasmic reticulum Microvilli Secretory vesicles Cilia Golgi apparatus Microtubule Microtubules L ysosomes

Cell Membrane (aka Plasma Membrane) Outer limit of the cell Controls what moves in and out of the cell, participates in signal transduction, and helps cells adhere to other cells Selectively permeable Phospholipid bilayer Water-soluble “heads” form surfaces (hydrophilic) Water-insoluble “tails” form interior (hydrophobic) Permeable to lipid-soluble substances (gases, steroid hormones) Cholesterol strengthens and stabilizes the membrane and makes it less permeable to water-soluble substances Proteins: Receptors Pores, channels and carriers Enzymes CAMS (cellular adhesion molecules) Self-markers

Cell Membrane

Cell Adhesion Molecules (CAMs) Guide cells on the move Selectin – allows white blood cells to “anchor” White blood cell Attachment (rolling) Selectin Integrin – guides white blood cells through capillary walls Carbohydrates on capillary wall Adhesion Adhesion receptor proteins Integrin Important for growth of embryonic tissue Blood vessel lining cell Exit Splinter Important for growth of nerve cells

Cytoplasm Cytoplasm - networks of membranes and organelles suspended in the cytosol (clear liquid) Cytoskeleton forms supportive framework and is made of protein rods and tubules

Organelles Endoplasmic Reticulum (ER) Connected, membrane-bound sacs, canals, and vesicles Transport system Rough ER Studded with ribosomes Functions in protein synthesis Smooth ER Lipid synthesis Added to proteins arriving from rough ER Break down of drugs ER membrane Ribosomes (a) Membranes Membranes Ribosomes Ribosomes Free floating in cytoplasm or connected to ER Composed of protein and RNA and provide structural support and enzyme activity to amino acids to form protein (b) (c)

Organelles Golgi apparatus Stack of flattened, membranous sacs Modifies, refines, packages and delivers proteins Vesicles Vesicles formed on ER travel to the Golgi apparatus which modifies their contents chemically. The vesicle may then move to the cell membrane and secrete its contents to the outside. Vesicles form a “delivery service,” carrying chemicals throughout the cell (vesicle trafficking).

Organelles Nuclear envelope Nucleus Cytosol Rough endoplasmic reticulum Golgi apparatus Secretion Transport vesicle Cell membrane (a) (b)

Organelles Mitochondria the powerhouses of the cell and contain enzymes needed for aerobic respiration. The inner membrane of the mitochondrion is folded into cristae which hold the enzymes needed in energy transformations to make ATP. Very active cells contain thousands of mitochondria.

Organelles Inner membrane Cristae Outer membrane (a) (b)

Organelles Lysosomes Centrosome Enzyme-containing sacs Digest worn out cell parts or unwanted substances “garbage disposals” Centrosome Two rod-like centrioles Used to produce cilia and flagella Distributes chromosomes during cell division Peroxisomes Enzyme-containing sacs that function in the synthesis of bile acids Break down organic molecules

Organelles Cilia Short hair-like projections abundant on the free surfaces of certain epithelial cells Propel substances on cell surface Flagellum Long tail-like projection Provides motility to sperm

Organelles Microfilaments and microtubules Thin rods and tubules Support cytoplasm Allows for movement of organelles Microfilaments: made of actin, cause various cellular movements. Microtubules: made of the globular protein tubulin, are attached in a spiral to form a long tube. Mitochondrion Nucleus Vesicle Rough endoplasmic reticulum Cell membrane (a) Microfilaments Ribosome Microtubules (b)

Cell Nucleus Control center of the cell Nuclear envelope Porous double membrane Separates nucleoplasm from cytoplasm Nucleolus Dense collection of RNA and proteins Site of ribosome production Nucleus Nuclear envelope Chromatin Consists of all the cell’s chromosomes, each containing DNA wound around proteins Fibers of DNA and proteins Stores information for synthesis of proteins Nucleolus Chromatin Nuclear pores (a)