Eukaryotic Cells

Animals & Plants

The Cell

Building block of the all organisms, from single-celled to human.

200 Types of cells in the human body, categorized by cell shape.

Cell size limited by the volume and surface area ratio. If the cell is too big, it cannot support itself or

absorb nutrients/excrete wastes effeciently.

Classes of Cell Shapes

Squamous: Thin & flat cells covering surfaces or lining “tubes” Example: Skin, lining of the esophagus

Cuboidal: Square or cube shaped; approximately as wide as they are tall. Example: Liver cells

Columnar: Much taller than they are wide. Example: Lining of the intestines

Spheroid: Egg cells and fat cells; round or oval. Fusiform: Thick in the middle and tapered towards the

ends. Example: Smooth muscle cells

Stellate: Star-shaped cells. Example: Some nerve cells

Cell Theory

Based on Robert Hook, Theordore Schwann, & Louis Pasteur

Modern Cell Theories’ Generalizations: All organisms are composed of cells and cell products. The cell is the simplest structural and functional unit of

life. All functions and structures are ultimately due to the

activities of cells. Cells come only from pre-existing cells. The cells of all species have many fundamental

similarities.

General Cell Structure Eukaryotic cells all

have the following general structures: Cell Membrane Cytoplasm Nucleus Intracellular Organelles

Cell Membrane All cells are

surrounded by a plasma membrane made up of proteins and lipids

Bilayer of lipids with diverse proteins embedded in it

98% of membrane molecules are lipids 75% of these are

phospholipids

Cell Membrane Phospholipid Bilayer:

Two phospholipid layers thick

Hydrophilic heads facing the water on each side of the cell membrane.

Hydrophobic tails directed toward the center of the membrane (avoiding the water)

Membrane is dynamic and “fluid”

Cell Membrane Cell Membrane is the target site of many

pharmaceutical agents Proteins only make up 2% of the

molecules in a plasma membrane, but are larger then lipids and make up around 50% of the membrane weight.

Cell Membranes

Integral or Transmembrane Proteins: Pass across the plasma membrane and are responsible for many functions. Integral proteins function as… Receptors: Specific for one messenger Second-messenger Systems: Triggered by

messengers that bind with surface receptors Enzymes: Produce second messengers and help with

digestion in the small intestine Channel Proteins: These molecules have “pores” &

allow passage of water & other solutes through the membrane

Carriers: Also called “PUMPS” they actively transport molecules into the cell utilizing ATP in the process

Glycocalyx The “fuzzy” coat

external to the plasma membrane on all animal cells, including humans

Acts as an “identification” tag that enables the body to distinguish its own healthy cells from transplanted tissue, invading organism, and diseased cells.

Surface Extensions Surface extensions

aid in absorption, movement, and sensory processes.

Microvilli: Extensions of the plasma membrane; serve primarily to increase a cell’s surface area; best developed in cells that specialized in absorption (e.g. the cells lining the small intestine)

Surface Extensions Cilia: Multiple hair-

like processes that project from the surface of the cell Nonmotile Primary

Cilium: Nearly every human cell has a single nonmotile primary cilium.

Motile Cilia: Less widespread but occur widely in respiratory tract and fallopian tubes; “wave” to help move materials through internal tubes

Surface Extensions Flagella: A single

whip-like structure much longer than cilia. The only functional

flagellum in humans is the tail of the sperm cell.

Cytoplasm Cytoplasm: The fluid

that is contained inside the plasma membrane. Crowded with fibers,

tubules, passageways, and compartments.

Contains cytoskeleton (supportive framework) and intracellular organelles embedded in the cytosol or Intracellular fluid (ICF).

Extracellular Fluid Extracellular fluid

(ECF) is the fluid outside the cell.

Nucleus Nucleus: The

structure at the center of the cell containing the genetic information for the organism.

Nucleus Nucleic Acid: DNA or

RNA. DNA is the principle

type of nucleic acid contained in the cell nucleus.

DNA contains the genetic code for organisms and is involved in protein synthesis, cell division (mitosis), and reproduction of the organism.

Plasma Membrane Plasma Membrane:

Acts as a barrier and gateway between the cytoplasm and the extracellular fluid.

Selectively Semi-Permeable: The plasma membrane lets some things through and blocks other things; this is tremendously important in clinical practice!

Plasma Membrane

Methods of Transporting Substances: Passive and Active transport.

Passive Transport includes… Filtration Diffusion Osmosis

Active Transport requires ATP and includes… Active transport Vesicular transport

Filtration

Filtration: The process by which particles are driven through a filter, or selectively permeable membrane, via hydrostatic pressure exerted on a membrane by water. Example: Coffee Filter

Weight of water forces water through the grounds and coffee filter.

Filter holds back the larger particles (coffee grounds) Most important filtration in the human body occurs in

the capillary wall – transfer of water, salts, nutrients, etc. from blood stream to tissue and extracellular fluid & wastes to kidneys

Simple Diffusion Simple Diffusion: The net

movement of particles from an area of higher concentration to an area of lower concentration.

The result of constant, spontaneous movement of molecules known as Brownian Movement.

Concentration Gradient: When the concentration of a substance differs from one point to another.

Movement occurring down or with the concentration gradient is movement from the higher concentration area to the lower.

Simple Diffusion IF the membrane is semi-permeable and

permeable to that substance, than diffusion will occur.

IF the membrane is not permeable to the substance, it will not diffuse across the membrane.

Diffusion Rates

Diffusion Rates: Important to cell survival because they determine how quickly a cell can acquire nutrients or rid itself of wastes.

Factors affecting diffusion rate: Temperature: The higher the temp, the faster the diffusion

rate. Molecular Weight: Heavy molecules diffuse more slowly. Membrane Surface Area: The more surface area the faster

the diffusion rate. “Steepness” Of Concentration Gradient: The greater the

concentration difference, the faster the diffusion. Membrane Permeability: The permeability of the

membrane. Diffusion Distance: Distance diffusion occurs across. Facilitated Diffusion: Whether a solute binds to a specific

transporter (changes the shape and releases the solute on the other side of the membrane).

Osmosis Osmosis: The

diffusion of water through a selectively permeable membrane from the area of higher concentration to the area of lower concentration. The higher solvent

(water) concentration area has a low solute concentration.

The higher solute concentration has a low solvent concentration.

Tonicity Tonicity: The ability of a solution to affect

the fluid volume and the pressure in a cell. If a solute cannot pass through a plasma

membrane, but remains more concentrated on one side of the membrane than on the other, it triggers osmosis.

Tonicity

Hypotonic Solution: Area surrounding a cell has a lower concentration of nonpermeating solutes than the intracellular fluid. Cells absorb water, swell, and lyse (burst).

Hypertonic Solution: Area surrounding cell has a higher concentration of nonpermeating solutes than the intracellular fluid. Cells will lose water and crenate (shrivel).

Isotonic Solution: The area surrounding the cell has the same total concentration of nonpermeating solutes as the intracellular fluid. Cells will neither loose nor gain water molecules & do

not change size or shape.

Active Transport

Active Transport: The carrier-mediated transport of a solute through a plasma membrane but against a concentration gradient. Utilizes ATP and energy to move against the

normal concentration gradient from an area of low concentration to high concentration.

Example: The sodium-potassium pump.

Sodium-Potassium Pump

Used to regulate the balance of sodium and potassium within the cell.

1 ATP molecule exchanges 3 sodium atoms (Na+) for 2 potassium (K+) atoms. Keeps the potassium higher and sodium lower within the

cell. Plasma membrane continuously leaks Na+ and K+, so

the pump keeps the balance corrected. Na+ and K+ play a critical part in nerve impulses and

cardiac function.

Vesicular Transport

Vesicular transport moves large particles and droplets of fluid or numerous molecules through the plasma membrane all at once.

Endocytosis: Vesicular processes that bring matter into the cell. Two types: Phagocytosis: “Cell eating” where foreign particles are

engulfed (e.g. monocytes) Pinocytosis: “Cell drinking” where droplets of

extracellular fluid containing molecules used by cells are taken in.

Exocytosis: Vesicular processes that release matter from the cell.

Organelles

Organelles: The internal structures within a cell that carry out specific functions. Some are surrounded by one or two layers of a unit

membrane and are therefore referred to as “membranous organelles.”

Membranous Organelles: Nucleus, mitochondria, lysosomes, endoplasmic reticulum, golgi complex.

Non-Membranous Organelles: Ribosomes, centrosome, centrioles, basal bodies.

Membranous Organelles: Nucleus

Nucleus: The largest organelle, spheroid in shape. Most cells have a single

nucleus Nucleus surrounded by

nuclear envelope or membrane

Nucleoplasm: The material contained within the nucleus. Includes…

Chromatin (DNA and protein)

Nucleoli (produces ribosomes)

Membranous Organelles: Endoplasmic Reticulum (ER)

Endoplasmic Reticulum: “Little network within the cytoplasm”

A system of interconnected channels that extend through the cytoplasm and reach the nuclear membrane. Channels called Cisternae

Membranous Organelles: Endoplasmic Reticulum (ER)

Two Types: Rough Endoplasmic

Reticulum: Channels are covered with ribosomes (synthesize proteins).

Smooth Endoplasmic Reticulum: Extends from the Rough ER to form membranous tubules network.

Smooth ER synthesizes steroids & lipids

Rough ER is responsible for detoxifying alcohol and other drugs

Rough ER most abundant in cells that produce large amounts of proteins – such as those in the digestive glands

Membranous Organelles: Golgi Complex

Golgi Complex: The small system of cisternae which synthesize carbohydrates and put the finishing touches on protein and glycoprotein synthesis.

Membranous Organelles: Golgi Complex

Primary function is to package protein into membrane-bound golgi vesicles

Some become secretory vesicles and store cell products such as breast milk & digestive enzymes

Some of these can become lysosomes

Membranous Organelles: Lysosomes

Lysosomes: A package of enzymes which are bounded by a single unit membrane – usually produced by the Golgi complex Primary function is to

hydrolyze or digest proteins, nucleic acids, complex carbohydrates, and phospholipids

Autophagy: The digestion of surplus cells by their own lysosomal enzymes (as in the liver).

Membranous Organelles: Peroxisomes

Peroxisomes: Resemble lysosomes but are smaller and contain different enzymes (oxidase) and are not produced by the Golgi Complex\

Membranous Organelles: Mitochondria

Mitochondria: Organelles specialized for synthesizing ATP Power-house of cells Bean shaped Outer and inner membranes Generate most of the cell’s

ATP Cristae contain enzymes for

aerobic respiration Matrix enclosed in the

inner membrane; site of oxidation of organic molecules; contains DNA and ribosomes.

Non-Membranous Organelles: Ribosomes

Ribosomes: Small granules of protein and ribosomal RNA found in several places in the cytoplasm: On Rough ER In the Nuclear Envelope Floating freely in

cytoplasm Primary function is

protein synthesis.

Non-Membranous Organelles: Ribosomes

Responsible for assembling amino acids based on messenger RNA codes.

Non-Membranous Organelles: Centrioles

Centrioles: A short cylindrical assembly of microtubules. 2 centrioles lie at right

angles to each other within a small clear area of cytoplasm called the centrosome

Play a role in cell division – Mitosis

Cytoskeleton

Cytoskeleton: A collection of protein filaments and cylinders that determine the shape of a cell. Lend structural support Organize cellular contents Help move stuff through the cell Contribute to movements of the cell Connected to integral proteins of the plasma

membrane Made up of microfilaments and microtubules

Inclusions

Inclusions: 2 Kinds Stored cellular products such as glycogen

granules or fat droplets OR foreign bodies such as dust particles

NO unit membrane Not essential to cell survival Not organelles Temporary structures; not permanent

Mitosis Mitosis: The process by

which cells divide to grow or to repair damage. 4 Stages: Prophase Metaphase Anaphase Telophase

Mitosis Prophase:

Condensing of chromatin fibers into chromatid pairs

Mitosis Metaphase: The

chromatid pairs line up along the metaphase plate

Mitosis Anaphase: The

centromeres joining the chromatids split, identical sets move to opposite sides of the cell

Mitosis Telophase: Nucleoli

reappear around two new sets of chromosomes and cell begins to split for cytokinesis – the division of the cell material.