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CELLS. Cell Theory, Microscopy,Prokaryotes, Eukaryotes, Animal Cell, Plant Cell. CELL THEORY. All living things are composed of cells and their products. New cells are formed only by the division of existing cells.

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Cells

CELLS

Cell Theory, Microscopy,Prokaryotes, Eukaryotes, Animal Cell, Plant Cell


Cell theory

CELL THEORY

  • All living things are composed of cells and their products.

  • New cells are formed only by the division of existing cells.

  • The cell is the functioning unit of life; the chemical reactions of life take place within cells.


Microscopy

Microscopy


Compound light microscopes

Compound light microscopes

Use visible light and a combination of lenses to magnify objects up to 1000 times.


Electron microscopes

Electron microscopes

Use a beam of electrons, instead of light, to produce image


Transmission electron microscope tem

Transmission Electron Microscope (TEM)

  • Extremely thin sections

  • Electrons pass through some parts of specimen and not others, forming image

  • Good for organelle structure

  • Magnifies up to 250,000 times


Tem image

TEM image


Le 6 4

1 µm

Scanning electron

microscopy (SEM)

Cilia

LE 6-4

Longitudinal

section of

cilium

Transmission electron

microscopy (TEM)

Cross section

of cilium

1 µm


Scanning electron microscope

Scanning Electron Microscope

  • Scans sample with a beam of electrons.

  • Magnifies up to 100,000 times


Sem image

SEM image


Advantages of light microscopes

Advantages of light microscopes

  • Easy, inexpensive sample preparation

  • Allows examination of live material (movement; no artificial structures)

  • Colors can be seen (natural and stains)

  • Field of view is relatively large (1.8 mm at 100X magnification)


Advantage of electron microscopes

Advantage of electron microscopes

  • Excellent resolution, allowing for extremely high magnification

    • This permits examination of very small objects and details of cell structure


Prokaryotic cells

Prokaryotic Cells


Prokaryotic cells bacteria

Prokaryotic Cells (Bacteria)

  • Pro – before

  • Karyon – nucleus

    Prokaryote = Before Nucleus


Electron microscope views of prokaryotic cells

Electron microscope views of prokaryotic cells


The outer layer has 2 parts

The outer layer has 2 parts

  • Cell wall – forms protective outer layer which prevents damage from outside and bursting if internal pressure is high

  • Plasma membrane – controls entry and exit of substances, some by active transport


Cells1

CELLS

Eukaryotic Cells


Prokaryotic vs eukaryotic cells

Prokaryotic vs. Eukaryotic Cells

  • Cells are prokaryotic or eukaryotic

  • Prokaryotic cells are Bacteria

  • Protozoa, Fungi, Animals, and Plants all consist of eukaryotic cells


Prokaryotic vs eukaryotic cells1

Prokaryotic vs Eukaryotic Cells

  • Similarities

    • Plasma membrane

    • Semifluid substance called the cytoplasm

    • DNA - Chromosomes (carry genes)

    • Ribosomes (make protein)

      Differences

  • Prokaryotic cells have no nucleus

  • Prokaryotic cells lack membrane-bound organelles

  • Eukaryotic cells have DNA in a nucleus that is bound by a membrane (nuclear envelope)

  • Eukaryotic cells have membrane-bound organelles

    • Organelle: one of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells


Le 6 7

Surface area increases while

Total volume remains constant

5

1

1

Total surface area

(height x width x

number of sides x

number of boxes)

LE 6-7

750

6

150

Total volume

(height x width x length

X number of boxes)

125

125

1

Surface-to-volume

ratio

(surface area  volume)

6

6

1.2


Plasma membrane must have sufficient surface area to service the volume of the cell

Plasma membrane must have sufficient surface area to service the volume of the cell

  • The plasma membrane is a selective barrier that allows passage of oxygen, nutrients, and waste


A panoramic view of the eukaryotic cell

A Panoramic View of the Eukaryotic Cell

  • A eukaryotic cell has internal membranes that partition the cell into organelles

  • Plant and animal cells have most of the same organelles


Le 6 9a

ENDOPLASMIC RETICULUM (ER

Nuclear envelope

Flagellum

Rough ER

Smooth ER

NUCLEUS

Nucleolus

Chromatin

Centrosome

Plasma membrane

CYTOSKELETON

Microfilaments

LE 6-9a

Intermediate filaments

Microtubules

Ribosomes:

Microvilli

Golgi apparatus

  • In animal cells but not plant cells:

  • Lysosomes

  • Centrioles

  • Flagella (in some plant sperm)

Peroxisome

Mitochondrion

Lysosome


Le 6 9b

Nuclear

envelope

Rough

endoplasmic

reticulum

NUCLEUS

Nucleolus

Chromatin

Smooth

endoplasmic

reticulum

Centrosome

Ribosomes

(small brown dots)

Central vacuole

Golgi

apparatus

Microfilaments

Intermediate

filaments

CYTOSKELETON

LE 6-9b

Microtubules

Mitochondrion

Peroxisome

Chloroplast

Plasma

membrane

  • In plant cells but not animal cells:

  • Chloroplasts

  • Central vacuole

  • Cell wall

  • Plasmodesmata

Cell wall

Plasmodesmata

Wall of adjacent cell


Le 6 29a

Proteoglycan

complex

EXTRACELLULAR FLUID

Collagen

fiber

Extra-Cellular Matrix

Fibronectin

LE 6-29a

Plasma

membrane

CYTOPLASM

Micro-

filaments

Integrin


Membranes

Membranes

Structure and Function


Plasma membrane

Plasma Membrane

  • Also known as “cell membrane”

  • Surrounds all cells

    • In cells with cell walls, the plasma membrane is found inside the cell wall


Plasma membrane is a bilayer of phospholipids

plasma membrane is a bilayer of phospholipids


Phospholipid molecules have a hydrophilic region and a hydrophobic region

Phospholipid molecules have a hydrophilic region and a hydrophobic region


Le 7 2

  • Most cells have watery environment on both sides of membrane

  • Water attracts the polar phosphate ends of the phospholipids

  • Phospholipids align to form double layer membrane, with polar ends on outside of each layer of the membrane

  • Non-polar tails are inside the bilayer

LE 7-2

WATER

Hydrophilic

head

Hydrophobic

tail

WATER


Le 7 3

Hydrophilic region

of protein

LE 7-3

Phospholipid

bilayer

Hydrophobic region of protein


Le 7 4

Extracellular

layer

Proteins

Knife

LE 7-4

Plasma

membrane

Cytoplasmic

layer

Extracellular layer

Cytoplasmic layer


Membrane proteins

Membrane Proteins

  • A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

  • Peripheral proteins are not embedded, they are attached to the membrane surface

  • Integral proteins penetrate the hydrophobic core and often span the membrane


Le 7 7

Fibers of

extracellular

matrix (ECM)

Glycoprotein

Carbohydrate

Glycolipid

EXTRACELLULAR

SIDE OF

MEMBRANE

LE 7-7

Cholesterol

Peripheral

proteins

Microfilaments

of cytoskeleton

Integral

protein

CYTOPLASMIC SIDE

OF MEMBRANE


Le 7 5c

LE 7-5c

Cholesterol

Cholesterol within the animal plasma membrane


Functions of membrane proteins

Functions of Membrane Proteins

  • Proteins determine most of the membrane’s functions. They serve as:

    • Hormone binding sites

    • Enzymes

    • Cell–Cell joining & Communication

    • Channels for passive transport

    • Pumps for active transport


Transport across the plasma membrane

Transport across the plasma membrane

Remember…..

The plasma membrane controls what comes in and out of the cell.


Selective permeability

Selective Permeability

  • Most biologic membranes are selectively or semi-permeable

    • This means that they allow some things through, but not others


Permeability

Permeability

  • If substance CAN diffuse across membrane, membrane is permeable to that substance

  • If substance CANNOT diffuse across membrane, membrane is impermeable to the substance


One way that some substances can cross the membrane is by diffusion

One Way that Some Substances can Cross the Membrane is by Diffusion

  • Definition of diffusion:

    • Movement of particles from area where they are more concentrated to area where they are less concentrated


Diffusion cont d

Diffusion, cont’d.

  • Diffusion is the tendency for molecules to spread out evenly into the available space.

  • Substances diffuse down their concentration gradient, that is, from an area where they are more highly concentrated to an area where they are less concentrated.


Le 7 11a

Molecules of dye

Membrane (cross section)

WATER

LE 7-11a

Net diffusion

Net diffusion

Equilibrium

Diffusion of one solute


Le 7 11b

LE 7-11b

Net diffusion

Net diffusion

Equilibrium

Equilibrium

Net diffusion

Net diffusion

Diffusion of two solutes


Diffusion cont d1

Diffusion, cont’d.

  • Diffusion across plasma membrane is a form of passive transport, because no work must be done to move substances down the concentration gradient

    • Passive Transport: transport across the membrane that requires no energy from the cell.


Diffusion cont d2

Diffusion, cont’d.

  • Hydrophobic, non-polar molecules can dissolve in and cross a membrane unassisted.

    • Hydrocarbons

    • CO2

    • O2

Animation: Diffusion


Facilitated diffusion

Facilitated Diffusion

  • Diffusion of some other substances across the cell membrane is assisted, or “facilitated,” by protein channels within the membrane

  • Usually involves large or strongly charged molecules, which cannot dissolve in the lipid bilayer.


Facilitated diffusion1

Facilitated diffusion

  • Even though movement is facilitated, it will still only occur from region of high concentration to region of low concentration.

  • Facilitated diffusion is still PASSIVE transport


Examples of molecules moving via facilitated diffusion

Examples of molecules moving via facilitated diffusion

  • Some ions and polar molecules (e.g. water)

  • Aquaporins are channel proteins which greatly speed up the diffusion of water.

Animation: Membrane Selectivity


Osmosis

Osmosis

  • Definition: diffusion of water across a selectively permeable membrane

  • Water diffuses down its own concentration gradient, which is affected by solute concentration.

  • Binding of water molecules to solute particles lowers the proportion of unbound water that is free to cross the membrane.

Osmosis and water balance in cells, parts 1 and 2


Le 7 12

Lower

concentration

of solute (sugar)

Higher

concentration

of sugar

Same concentration

of sugar

H2O

LE 7-12

Selectively

permeable mem-

brane: sugar mole-

cules cannot pass

through pores, but

water molecules can

Osmosis


Cells

Tonicity is the ability of a solution to cause a cell to gain or lose water

  • Isotonic solution: solute concentration is the same as that inside the cell; no net water movement across the plasma membrane

  • Hypertonic solution: solute concentration is greater than that inside the cell; cell loses water

  • Hypotonic solution: solute concentration is less than that inside the cell; cell gains water


Solutions inside and outside cell are isotonic

Solutions inside and outside cell are isotonic

10% salt, 90% H2O

10% salt 90% H2O


Solution outside cell is hypertonic to that inside cell

Solution outside cell is hypertonic to that inside cell

20% salt, 80% H2O

20% salt, 80% H2O

Salt sucks.

10% salt 90% H2O


Solution outside cell is hypotonic to that inside cell

Solution outside cell is hypotonic to that inside cell

5% salt, 95% H2O

Salt sucks.

10% salt, 90% H2O


Osmotic pressure

Osmotic Pressure

  • Created when water diffuses into a cell

  • In animals and other organisms without cell walls, cells swell and may burst


Osmotic pressure in cells without walls cont d

Osmotic Pressure in Cells without Walls, cont’d.

  • To maintain their internal environment, organisms without cell walls must have adaptations for osmoregulation, the control of water balance

  • The protist Paramecium, which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump


Le 7 14

50 µm

Filling vacuole

LE 7-14

50 µm

Contracting vacuole

Video: Paramecium Vacuole


Osmotic pressure in cells without walls cont d1

Osmotic Pressure in Cells without Walls, cont’d.

  • Plasmolysis occurs when water diffuses out of a cell

  • Cells shrink


Osmotic pressure in cells with walls

Osmotic Pressure in Cells with Walls

  • Cell walls help maintain water balance

  • In a hypotonic solution, turgor pressure causes the cell to swell until the wall opposes uptake; the cell is now turgid (firm)

Video: Turgid Elodea


Osmotic pressure in cells with walls cont d

Osmotic Pressure in Cells with Walls, cont’d.

  • If a plant cell and its surroundings are isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt

  • In a hypertonic environment, plant cells lose water (plasmolysis); vacuoles collapse, and eventually, the membrane pulls away from the wall.

Video: Plasmolysis


Plasmolysis in red onion cells

Plasmolysis in Red Onion Cells

Cells in hypertonic solution; water has diffused out of cells, causing them to shrink away from their cell walls

Cells in hypotonic solution; water has diffused into cells, creating turgor pressure


Plasmolysis in cucumber cells

Plasmolysis in Cucumber Cells

Cells in pure water environment; water has diffused into cells, creating turgor pressure

Cells in hypertonic environment; water has diffused out of cells, causing them to shrink away from their cell walls


Le 7 13

Isotonic solution

Hypertonic solution

Hypotonic solution

Animal

cell

H2O

H2O

H2O

H2O

Shriveled

Normal

Lysed

LE 7-13

Plant

cell

H2O

H2O

H2O

H2O

Flaccid

Plasmolyzed

Turgid (normal)

Osmosis and water balance in cells, parts 3 and 4


Active transport

Active Transport

  • Involves movement of substances across the cell membrane from area of LOWER concentration to area of HIGHER concentration

  • Since movement is against the concentration gradient, it REQUIRES ENERGY from the cell


Active transport using membrane protein pumps

Active Transport using Membrane Protein “Pumps”

  • Active transport of small molecules and ions is usually carried out by membrane proteins that act as energy-requiring pumps

  • Changes in the shape of these membrane proteins play an important role

Activity – Active Transport


Active transport by endocytosis and exocytosis

Active Transport by Endocytosis and Exocytosis

  • Endocytosis – Requires Energy!

    • Materials taken into the cell by means of infoldings or pockets of the cell membrane

    • Pocket breaks loose and forms vacuole within the cytoplasm

    • Vacuole may fuse with a lysosome, so material in vacuole can be digested


Cells

  • http://bio.winona.msus.edu/bates/genbio/images/endocytosis.gif


Exocytosis requires energy

Exocytosis – Requires Energy!

  • Way for cell to release large amount of material from a vacuole to outside of cell

  • Membrane surrounding the vacuole fuses with cell membrane

  • Contents of vacuole expelled out of the cell


Cells

Activity – Endocytosis and Exocytosis

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/endocytosis.gif


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