A&P 1 Ch 3 PP: Cells

Cells

Cells are the smallest units that possess the characteristics of life

Cells and homeostasis

Maintain homeostasis of the internal environment

Cell

The cell is the basic unit of structure and function in the body.

Differentiated

Cells that have developed specialized characteristics are said to be differentiated.

Cell size and shape

Cells vary in size and shape; structure and function are inter-related.

A Composite Cell

There is no typical cell, but a composite cell shows the components found in most cells.

3 Major Parts Found in Most Cells

Nucleus; Cytoplasm; Cell membrane

Cytoplasm

Cytoplasm consists of organelles, with specific functions, suspended in a liquid called cytosol.

Cell Membrane

Maintains the integrity of the cell, is fluid (moves), controls entry and exit of substances

Cell membrane framework

Cell membrane framework is a phospholipid bilayer:

Hydrophilic heads

Water-soluble (hydrophilic) heads form surfaces.

Hydrophobic tails

Water-insoluble (hydrophobic) tails form interior.

Phospholipid bilayer permeability

Bilayer is permeable to lipid-soluble substances, but impermeable to water-soluble substances.

Cholesterol

Cholesterol stabilizes membrane, helps keep it impermeable to water-soluble substances.

Fluid mosaic

Some lipids and proteins can move; “fluid mosaic” properties.

Membrane proteins

Membrane proteins have many functions:

Membrane protein functions

Pores, channels, receptors, enzymes, cell contact and identification, CAMs (Cell Adhesion Molecules).

Carbohydrates

Cell recognition and interaction, self markers.

Cytoplasm

Cytoplasm consists of networks of membranes and organelles suspended in cytosol.

Cytoplasm

Cytoplasm = cytosol + organelles

Cytosol

Fluid portion of the cytoplasm.

Organelles

Tiny solid structures with specific functions in the cell.

Cytoskeleton

Cytoplasm contains the cytoskeleton, a supporting framework of protein rods and tubules.

Ribosomes

Composed of protein and R N A.

Ribosomes location

Free in cytoplasm or on R E R.

Ribosomes function

Provide structural support and enzyme activity to link amino acids in protein synthesis.

Endoplasmic Reticulum (E R)

Membrane-bound sacs that are interconnected with canals, vesicles.

Endoplasmic Reticulum function

Tubular transport system.

Rough E R

Rough E R contains ribosomes, conducts protein synthesis.

Smooth E R

Smooth E R does not have ribosomes; conducts lipid synthesis.

Vesicles

Membranous sacs.

Vesicles function

Store or transport substances.

Golgi Apparatus

Sacs of flattened, membranous sacs.

Golgi Apparatus function

Refines, packages, and delivers proteins made on the R E R.

Mitochondria

Membrane-bound, fluid-filled sacs

Mitochondria function

House chemical reactions that extract energy from nutrients (cellular respiration, which produces A T P)

Mitochondria

Called the “powerhouse of the cell”.

Lysosomes

Small membranous sacs

Lysosomes function

Contain enzymes that digest proteins, carbohydrates, nucleic acids, bacteria, debris, worn out cell parts

Lysosomes

“Garbage disposals” of cell.

Peroxisomes

Membranous sacs similar to lysosomes

Peroxisomes function

Contain enzymes that digest lipids, alcohol, hydrogen peroxide.

Microfilaments, Microtubules & Intermediate Filaments

Thread-like structures in cytoplasm.

Microfilaments, Microtubules & Intermediate Filaments function

Create the cytoskeleton.

Microfilaments

Tiny rods of actin; provide cellular movement, such as muscle contraction.

Microtubules

Larger tubes of tubulin.

Microtubules function

Rigidity maintains cell shape.

Microtubules

Make up cilia, flagella, and centrioles.

Microtubules function

Help move organelles.

Intermediate filaments

Composed of several proteins.

Intermediate filaments

A cytoskeletal structure.

Intermediate filaments function

Support nuclear envelope.

Centrosome

“Central body;” consists of 2 centrioles.

Centrosome location

In cytoplasm, near nucleus.

Centrioles

Centrioles are cylindrical, composed of microtubules.

Centrioles function

Centrioles produce spindle fibers during cell division, which distribute chromosomes to forming daughter cells.

Cilia

Motile extensions of cell membrane.

Cilia structure

Consist of microtubules

Cilia movement

Beat back and forth in coordinated manner.

Cilia function

Propel mucus in respiratory tract, propel egg toward uterus.

Flagella

Another type of motile extension from cell membrane.

Flagella structure

Similar in structure to cilia, but much longer.

Flagellum function

Flagellum causes the entire cell to move.

Flagellum in human cells

Tail of a sperm cell is the only flagellum in a human cells.

Number of flagella

Each cell has only 1 flagellum.

Cell Nucleus

Contains genetic material and controls cell activities.

Nuclear envelope

Porous double-layered membrane.

Nuclear envelope function

Separates nucleoplasm from cytoplasm.

Nuclear pores

Nuclear pores allow passage of certain substances.

Nucleolus

Dense body of R N A and protein.

Nucleolus function

Site of ribosome production.

Chromatin

Consists of cell’s chromosomes, each containing D N A wound around proteins.

Chromatin function

Stores information for protein synthesis.

Physical (Passive) Processes

Do not require A T P

Simple Diffusion

Movement of atoms, molecules, or ions, from region of higher concentration to region of lower concentration.

Facilitated diffusion

Diffusion across the cell membrane through ion channels or transporters.

Simple and Facilitated diffusion

Simple and Facilitated diffusion move substances from an area of high concentration to an area of low concentration.

Osmosis

Movement of water across a selectively permeable membrane from region of higher water concentration to region of lower water concentration

Osmosis

Movement of low solute concentration to high

Filtration

Process that forces molecules through membranes by exerting pressure.

Osmotic Pressure

Ability of osmosis to generate enough pressure to lift a volume of water

Osmotic pressure

Osmotic pressure increases as the concentration of impermeant solutes increases.

Isotonic Solution

Same osmotic pressure

Cells in an isotonic solution

Cells in an isotonic solution have no net gain or loss of water.

Hypertonic Solution

Higher osmotic pressure

Cells in a hypertonic solution

Cells in a hypertonic solution lose water and shrink

Hypotonic Solution

Lower osmotic pressure

Cells in a hypotonic solution

Cells in a hypotonic solution gain water and enlarge

Physiological (Active) Processes

Require A T P

Active transport

Movement from an area of low concentration to high concentration

Active transport

Active transport

Endocytosis

Endocytosis

Types of endocytosis

There are 3 types of endocytosis:

Pinocytosis

Membrane engulfs droplets of liquid.

Phagocytosis

Membrane engulfs solid particles.

Receptor-mediated endocytosis

Membrane engulfs specific substances, which have bound to receptor proteins on the membrane.

Exocytosis

Exocytosis

Transcytosis

Transcytosis

Interphase

A very active period in cell cycle.

Interphase

Cell grows.