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CELLSThe basic living, structural, and functional unit of all

organisms.

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Basic Cell Structure

Cell (Plasma) Membrane

Cytosol

Organelles

Nucleus

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Basic Cell

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Basic Cell Structures

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Cytosol

The semi-fluid material outside the nucleus and inside the plasma membrane

Suspends other elements

75% - 95% water

May contain organelles, large carbohydrates, fat, and protein molecules

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Function of Cytosol

Location of chemical reactions (anaerobic energy metabolism)

Synthesis of cellular substances

Packaging of chemicals for transport

Facilitates excretion of waste material

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The Cell (Plasma) Membrane

Thin structure that separates the internal cellular components from the external environment (acts as a barrier)

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Cell Membrane

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Structure of the Cell Membrane

Phospholipid bilayer

Hydrophilic phosphoric heads face outward

Hydrophobic fatty acid tails face inward

Also contains protein, cholesterol, and glycoproteins

Carbohydrates assist in cell identification/communication

Cholesterol increases strength of cell membrane

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Cell Membrane Proteins

Integral Proteins are proteins imbedded in the phospholipid bilayer

gates or channels are transport proteins

receptor sites for hormones

enzymes

cellular identity markers

Peripheral Proteins are loosely bound to plasma membrane

function not completely understood

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Cell Membrane Structures

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Cell Membrane Proteins

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Functions of the Cell Membrane

Flexible boundary

Facilitates contact with other cells and environment

Receptor sites - hormones, enzymes, neurotransmitters, nutrients, antibodies

Selectively permeable - mediates entrance and exit of material into and out of cell.

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Factors Influencing Permeability of Plasma Membrane

Size of molecules

Solubility in lipids

Charge on ions

Presence of carrier molecules

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Movement Across the Cell Membrane

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Intracellular Fluid

Fluid found in living cells

Comprises > 66% of body’s total water

Mostly water

may also contain potassium, phosphates, magnesium, chloride, and other ions

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The Extracellular Environment

Interstitial Fluid (Intercellular Fluid)

Fluid found in the microscopic spaces between cells

Plasma

Extracellular fluid within blood and lymph vessels

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Movement Across the Plasma Membrane

Passive Processes

No energy expenditure

Moves down a concentration gradient

High → low concentration

Active Processes

Requires energy expenditure

Moves against a concentration gradient

Low → high concentration

May utilize 40% of cells ATP supply

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Movement Across the Cell Membrane

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Passive Transport

Diffusion

Facilitated Diffusion

Osmosis

Dialysis

Filtration

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Diffusion

The movement of molecules from a higher concentration to a lower concentration. Does not require energy.

Particles tend to distribute themselves evenly within a solution

Ex: perfume, electrolytes

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Simple Diffusion

Unassisted process

Solutes are lipid-soluble materials or small enough to pass through membrane pores

Simple Diffusion

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Osmosis

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Simple diffusion of water

Highly polar water easily crosses the plasma membrane

Osmosis

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Osmosis

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Effects of Osmosis

Isotonic Solutions

Hypotonic Solutions

Hypertonic Solutions

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Tonic Solutions

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Tonic Solutions

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Facilitated Diffusion

Facilitated diffusion is the process of diffusion through the protein channels of the cell membrane

Substances require a carrier protein for passive transport

Ex: glucose

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Facilitated Diffusion

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Facilitated Diffusion

Dialysis

Dialysis is the diffusion of small solute particles through a selectively permeable membrane resulting in the separation of large and small solutes

Movement occurs from an area of high concentration to lower concentration

Example: Kidney dialysis

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Filtration

Filtration is the process of removing particles from a solution by allowing the liquid to pass through a membrane. It is influenced by gravity and hydrostatic pressure.

Water and solutes are forced through a membrane by fluid (hydrostatic pressure)

A pressure gradient must exist

solute-containing fluid is pushed from an area of high pressure to a lower pressure area

Example: Filtration in the glomerulus of the kidney nephron

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Dialysis vs. Filtration

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Dialysis

Filatration

Active Transport Processes

Transport substances that are unable to pass by diffusion

They may be too large

They may not be able to dissolve in the fat core of the membrane

They may have to move against a concentration gradient

Two common forms of active transport

Solute pumping

Bulk transport

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Active Transport Processes

Solute pumping

Amino acids, some sugars, and ions are transported by solute pumps

ATP energizes protein carriers, and in most cases, moves substances against concentration gradients

Ex: Sodium/Potassium Pump

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Active Transport Processes

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Active Transport Processes

Bulk Transport

Exocytosis

Endocytosis

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Active Transport Processes

Endocytosis occurs when the molecules are too big to enter the cell by diffusion or active transport, a vesicle is formed from the cell membrane.

Extracellular substances are engulfed by being enclosed in a membranous vesicle

Types:

Phagocytosis—cell eating

Pinocytosis—cell drinking

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Active Transport Processes

Endocytosis

Phagocytosis—cell eating

Large particles brought into cell by vacuole formation

Pinocytosis—cell drinking

Liquid material brought into cell by vacuole formation

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Active Transport Processes

Exocytosis

Any remaining particles from phagocytosis may be expelled from the cell when the vesicle joins with the cell membrane and the contents are removed from the cell.

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Nucleus

The “control center” of the cell

Usually the largest structure in the cell

Contains genetic information

Controls cellular function and structure

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Nuclear Structures

Nuclear Membrane

Nucleoplasm

Nucleolus

site of ribosome synthesis

Genetic Material DNA

Chromatin contains DNA in thread-like form (cell is not dividing)

Chromosomes contains DNA in short, rod-like structures (cell is reproducing)

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Cell Nucleus

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Organelles

Specialized structures and portions of the cell with characteristic shapes that assume specific roles:

growth

repair

maintenance

control of cellular functions

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Organelles and Structures

Ribosomes

Endoplasmic Reticulum

Golgi Complex

Mitochondria

Lysosomes

Vacuoles

Peroxisomes

Microfilaments

Microtubules

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Organelles and Structures continued

Centrioles

Centrosomes

Flagella

Cilia

Microvilli

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Ribosomes

Appear as small, round, granular structures within the cell

Sites of protein synthesis by assembling the amino acids in the correct order.

Made up of special type of RNA called ribosomal RNA (rRNA)

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Ribosomes

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Endoplasmic Reticulum

Double membranous channels which are continuous with the nuclear membrane

Granular (Rough) Endoplasmic Reticulum

studded with ribosomes

site of protein synthesis

Agranular (Smooth) Endoplasmic Reticulum

free of ribosomes

site of lipid synthesis

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Functions of Endoplasmic Reticulum

Mechanical support and distribution of cytoplasm

Surface area for chemical reactions

Intracellular transport system

Storage of synthesized molecules

Protein (RER) and lipid (SER) synthesis

Detoxification of certain molecules

Release of calcium ions in muscles

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Endoplasmic Reticulum

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Golgi Complex (Bodies)

Flattened membranous sacs (4 - 8) stacked upon one another

Processes, packages, sorts, and delivers proteins to various parts of the cell

Secretion of lipid molecules from the cell

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Golgi Complex

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Mitochondria

Powerhouse of the cell

Small, spherical or rod-shaped structures

Sites of cellular respiration

conversion of glucose and lipids to ATP

aerobic energy metabolism

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Mitochondria

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Lysosomes

Nicknamed “suicide packets”

Small membrane enclosed spheres of digestive enzymes

Intracellular digestion

Autophagy is the process by which old worn out organelles are digested

Autolysis is the process by which lysosomes digest themselves

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Lysosomes

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Vacuoles

Fluid filled organelles enclosed by a membrane

Used to store digested cellular food or water

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Peroxisomes

Similar to lysosomes but much smaller

Usually found in the liver and kidney

Must have metabolic oxygen present to function properly

Role in detoxifying molecules (alcohol)

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The Cytoskeleton

Complex internal structure of cytoplasm that consists of small lattice-like or web-like structures

Provides support and maintains shape of the cell

Provides organization for chemical reactions

Assists in transport of substances through the cytosol

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Structures of the Cytoskeleton

Microfilaments fine, thread-like protein fibers

composed predominantly of a contractile protein called actin (association with the protein myosin is responsible for muscle contraction)

can also carry out cellular movements including gliding, contraction, and cytokinesis.

Intermediate Filaments provide tensile strength for the cell

Microtubules cylindrical tubes

composed of subunits of the protein tubulin

act as a scaffold to determine cell shape, and provide a set of "tracks" for cell organelles and vesicles to move on

form the spindle fibers for separating chromosomes during mitosis

when arranged in geometric patterns inside flagella and cilia, they are used for locomotion.

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Cytoskeleton Structures

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Centrioles

A pair of cylindrical structures located within the centrosome which serves as center of chromosome movement during cell division (mitosis)

Made of 9 microtubules in a cylindrical arrangement

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Centrosomes

Dense area of spherical cytoplasm generally located near the nucleus

Key to the division of cells and produce the spindle fibers that are required during metaphase of mitosis

Consists of two centrioles that are orientated at right-angles to each other

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Centrosomes/Centrioles

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Modifications of the Plasma Membrane

Microvilli

folds in the cell membrane

increase surface area for absorption of nutrients

Cilia

slender projections of the cell membrane

move substances across surface of the cell

Flagellum

single whip-like projection

used for cellular locomotion

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Flagellum/Cilium

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Cell Division

Process by which cells reproduce themselves

Results in increased number of cells or HYPERPLASIA

Nuclear Division

Somatic cell nuclear division (MITOSIS)

Sex cell nuclear division (MEIOSIS)

Cytoplasmic Division - Cytokinesis

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Results of Mitosis

Formation of two new daughter cells with identical genetic make up of parent cell

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Mitosis Overview

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Interphase

metabolic phase - between cell division

replication of chromosomes

replication of centrioles

time - highly variable from:

non existent

years

normally about 18 to 24 hours

Review of mitosis70

Cytokinesis

Division of the cytoplasm into two distinct cells each daughter cell will have their own plasma membrane, nucleus,

and organelles

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Meiosis

mechanism by which sperm and egg cells are produced

results in the production of sex cells GAMETES

Ovary ---> Oogenesis ---> Ovum

Testes ---> Spermatogenesis ---> Sperm

union and fusion of gametes is called fertilization

cell produced by fertilization - Zygote

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Meiosis vs Mitosis

Comparison of mitosis and meiosis

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