cell structure & function idea that cells are the basic units of living things began in 1800’s...

Cell Structure & Function

• Idea that cells are the basic units of living things began in 1800’s

• Cell theory:– All living things are composed of one or more

cells– Cells are organisms’ basic units of structure

and function– All cells come from pre-existing cellsAdvances in microscope technology have made

advances in cell biology possible

Chapter 7- Cell Structure & Function

• History-17th century:– Hooke first observed “cells” – van Leeuwenhoek used microscope to

observe living microscopic organisms


19th century: – Brown observed “nucleus”– Schleiden observes plants are made of cells– Schwann observes animals are made of cells– Virchow brings it all together: “All cells come

from cells”

Cell Size Limitations• Wide variety of cell sizes and shapes• Plasma membrane allows nutrients in and

wastes to leave (diffusion)• Within cell, both move by diffusion• Diffusion- fast and efficient over short

distances– Slow and inefficient as distances increase– Why can’t organisms be just one giant-sized

cell?

• Cube 1mm Cube 2mm Cube 4mm• SA- 6mm2 SA- 24mm2 SA- 96mm2

• V- 1mm3 V- 8mm3 V- 64mm3

• SA increase 4x 4x• Vol. increase 8x 8x

• As cell size increases, its volume increases faster than its surface area

• If cell size doubles, cell would require 8x more nutrients and produce 8x more wastes

• Surface area only 4x larger- not enough area for diffusion to take place efficiently (nutrients and wastes)

• Cell would either starve or poison itself

Cell Structure & Function

• Two basic cell types:– Prokaryotes: bacteria; found on every

continent, in every environment; range in size from 0.3 µm to 5 µm in diameter

– Eukaryotes: some unicellular and all multicellular organisms; 10-50 µm in diameter

– Difference? Eukaryotes contain membrane-bound organelles


• Prokaryotic cell structure:– No membrane bound organelles– Have organelles associated with protein

formation– (Most) Have rigid cell wall composed of

lipids, carbohydrates, and proteins– Have plasma membrane composed of

phospholipids– Have one circular chromosome


• May also contain plasmids: short, circular segments of DNA coding for a few genes

• Some have flagella, some have cilia; both used for locomotion (and sometimes feeding)

• Extremely diverse in metabolic processes– Many are autotrophs, some are

heterotrophs

Rod-shaped (Bacilli)

Sphere-shaped (cocci)

Spiral-shaped (spirochetes)


• Eukaryotic cell structure:Have specialized compartments

(organelles)Makes cells more efficient; enables a

division of labor within cells

Xvivo site


All have plasma membrane composed of phospholipids, proteins, and carbohydrates website

Some (plants, fungi, and some unicellular eukaryotes) have a cell wall composed of fibers of cellulose and other complex carbs

Chapter 6- Cell Structures


Within the plasma membrane, but outside the nucleus, is the cytoplasm

An organized gel of water, salts, and organic compounds

Supports cell functions and structure


Contains a system of protein fibers called the cytoskeleton– Microtubules- hollow protein tubes– Microfilaments- solid, flexible protein

fibers


Scattered throughout cytoplasm (in both cell types) are ribosomes

Composed of protein and RNA“Protein factories” of the cellHave major role in protein synthesis


Endoplasmic Reticulum (ER)- system of membranes; form tubes and channels throughout cell

Two types:Smooth ER- lipid synthesis; no ribosomesRough ER- surface ribosomes; protein

synthesis (cell membrane proteins)


Golgi Apparatus- series of membranous sacs that look like a stack of pancakes

Function:-Modification-Sorting-Packagingof proteins, lipids, carbohydrates“UPS” of the cell


Vesicles- spherical, membrane enclosed sacs

Transport materials around cell (and out of)Formed from Golgi apparatus and ER

membranes


Lysosomes- special vesicles found in animal cells and some other eukaryotes

Contain digestive enzymesBreak down macromolecules, old

organelles, foreign particlesRole in cell death


Chloroplasts- double-membrane organelles found in plant cells

Mitochondria- double-membrane organelles found in plant and animal cells

Both involved in energy production within the cell

Mitochondria: “Powerhouse” of the cell


Both organelles carry their own genetic information (DNA)

Evidence for Endosymbiont TheoryLynn Margulis-Stated that eukaryotes evolved from a

symbiosis btw two (or more) prokaryotes


Centrioles- tubular structures found in animal cells and some fungi and algae

Made up of microtubules

Function in cell division


Flagella- long bundles of microtubules

Function in movement of the cell“Whip-like”

Can have one, two, or many


Cilia- similar structure to flagella, but much shorter and more numerous

“Finger-like” cell projectionsFunctions:MovementFeeding


Nucleus-“Control center” of the cellDirects all cellular activityContains cell’s DNA (coded instructions for

making proteins)


Nuclear envelope-Double membrane surrounding nucleusNuclear pores-Allow material to pass back and forth

through envelopeChromatin-DNA bound to proteinsNucleolus- Site of ribosome synthesis & assembly

Plant-specific organelles- Cell Wall- Vacuoles: fluid-filled; store enzymes and

metabolic wastesCan take up to 90% of space of cell- Plastids: double-membrane bound

organelles; contain DNASome store starch or fats; others pigments


Cell interior (cytoplasm) surrounded by a cell membrane made of phospholipidsIn prokaryotes, plants and fungi:- is surrounded by a cell wall made of

carbohydrates and proteinsMaterials needed for functioning must

pass through these barriers and enter the cell


Functions:Cell Wall- protection and supportCell Membrane- regulation of materials

into and out of the cell; protection and support


Cell membrane structure:Phospholipid bilayer with surface and

embedded proteinsCell Membrane is Selectively PermeableAllows certain material through, and other

materials are kept out/in


Diversity of Cellular LifeUnicellular organisms = single celled

organismsCarry out all life processes

Ex.-Yeast Bacteria Some Algae

Colonial OrganismsCollection of genetically identical cells that

live together in a closely connected groupSome cells may specialize in performing

certain functions, such as energy conversion

Volvox modern day exampleOn the border btw unicellular and true

multicellular organisms


Multicellular organismsMany different cell types exist in complex

multicellular organismsAll cells carry out basic life functions, but

each type of cell often specializes as wellCell specialization-Cells develop in different ways to perform

different tasks


Examples of specialized cells:Animal cells-Blood Muscle Bone Nerve

Plant cells-Stomata Guard cells


Levels of OrganizationGroups of specialized cells working

together: tissueDifferent tissues may be organized into

organsOrgans may be grouped into organ

systemsSpecialized systems account for most of the

complexity of multicellular organisms


Systems necessary because:– A division of labor occurs among cells– Many individual cells cannot work

together without regulation and coordination

– Most cells are not in direct contact with outside environment


Concentration:Amount of solute (dissolved substance) per

amount of solvent (material solute is dissolved in)

12g of salt dissolved in 3 Liters waterConcentration = 4g/L


Concentration Gradient- difference in conc. between two areas in close proximity

Gradients occur across cell membranes (either naturally or cell makes gradient)


Molecules and atoms are in constant, random motion

Diffusion- movement of molecules from area of high concentration to an area of low concentration

Will continue until equilibrium (balance) is reached in concentration throughout solution


Osmosis- movement of water down a concentration gradient through a selectively permeable membrane

Rate depends on:– Size of the conc. gradient– Surface area of membrane


How Osmosis WorksIsotonic- solutions (across membrane) are

of equal concentrationsHypertonic- solution of higher concentration

Hypotonic- solution of lower concentration

Examples


Osmotic Pressure in Plant Cells


Osmotic Pressure in Animal Cells


Organisms must establish and maintain conc. of materials inside and outside the cell

Passive Transport- diffusion without input of energy

Active Transport- movement of material against the concentration gradient; requires energy


Passive TransportProcesses that do not require energy from

the cell:• Diffusion

- Simple Diffusion (thru the membrane)-Facilitated Diffusion (using membrane proteins as channels; molecule specific)

• Osmosis

Facilitated TransportUsed for molecules that cannot diffuse rapidly,

even when a conc. gradient presentMovement of these molecules across membrane

assisted by specific membrane proteins called carrier proteins

Molecules still move from high conc. to lower conc.Passive transport process (no energy involved)


Active TransportMovement of molecules/ions against their

concentration gradientRequires energy and use of transport

proteins or “pumps” in the membraneChange in protein shape makes this possibleMany substances could not enter or leave

cells without active transport process

Sodium-Potassium PumpWorks to move Na+ and K+ up their conc.gradientsOther pumps work in similar ways to moveimportant metabolicmaterials acrossmembranes


Exocytosis/EndocytosisVery large molecules moved into or out of

cell through special active transport mechanisms

Endocytosis- from environment to interiorExocytosis- from interior to environmentInvolves cell membrane either engulfing or

releasing material

cell structure & function idea that cells are the basic units of living things began in 1800’s...

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