Chapter 7

Chapter 7 – Cellular Structure & Function

Chapter 7.1 – Cell Discovery & Theory

pp. 182 - 186

Anton van Leeuwenhoek

• constructed the first microscope in the 1600’s (single magnifying lens)

• used a microscope to view, describe, and draw cells in pond water

Leeuwenhoek’s Microscope

Robert Hooke (1665)

• examined cork cells from the bark of an oak tree (dead plant cells)

• observed that the cork was composed of tiny, hollow boxes similar to the cells of a monastery

• called the structures cells

Hooke’s Microscope

Matthias Schleiden (1830’s)

• Observed a variety of plants

• Concluded that all plants are made of cells

Theodore Schwann (1830’s)

• Concluded that all animals are composed of cells

Rudolf Virchow

• stated that all cells arise from the division of preexisting cells

• Claimed that all living things come from other living things.

Light Microscope (100X)

Scanning Electron

Microscope (1500X)

Transmission Electron Microscope (62,000X)

Cellular Structure and Function

Utilizes a series of glass lenses and visible light to magnify an image

Magnifies images up to 1,000 times the actual size

Light Microscopes

Cellular Structure and Function

Utilizes magnets to aim a beam of electrons ata cell to produce an image

Magnifies images up to 500,000 times the actual size

9560x

Electron Microscopes

Cell Theory

1. All organisms are made of one or more cells.

• The amoeba is a unicellular (one-cell) organism.

Cell Theory (Continued)

2. The cell is the basic unit of organization of organisms.

3. All cells come from preexisting cells; a cell divides to form 2 identical (daughter) cells.

• Most organisms are multicellular.

Human skin cells

Blood cells traveling through the blood vessel

Two Basic Cell Types

• Prokaryotes (before nucleus)

• Eukaryotes (true nucleus)

Prokaryotic Cells

• do NOT have a true nucleus • do NOT have organelles surrounded

by a membrane • DNA is in a region called a nucleoid• most metabolic functions take place

in the cytoplasm• most prokaryotic organisms are

single-celled (ex. Bacteria)

Eukaryotic Cells

• have a true membrane-bound nucleus

• have membrane-bound organelles • different parts of the cell

specialize in different functions• majority of cells in the living world

are eukaryotic• either unicellular or multicellular

Eukaryotic Cell Prokaryotic CellNucleus- a distinct central organelle that contains the cell's genetic material (DNA)

Organelles-Specialized structures that carry out specific cell functions.

Organisms that are made up of eukaryotic cells are called eukaryotes.

Plasma Membrane-Special boundary that helps control what enters and leaves the cell.

Has no nucleus or organelles.

Organisms that are made up of prokaryotic cells are called prokaryotes. This includes most unicellular organisms like bacteria.

Organelles

• membrane bound structures within the cell that carry out specialized functions

• nucleus is the largest organelle

7.2 The Plasma (Cell) Membrane

pp. 187-190

Plasma (Cell) Membrane

• Like your home – sheltered and comfortable

• Plasma membrane- Barrier between the internal components of a cell and its environment

Homeostasis• the regulation of an internal

environment to provide conditions suitable for life

• living cells maintain homeostasis by controlling materials that enter and leave

• Examples In: water, glucose, other nutrients

• Examples Out: wastes

How does the cell membrane maintain homeostasis?

Selective Permeable Membrane

• Selective - the property of a membrane that allows some materials to pass through while keeping others out (doorway)

• Permeable – means easily pass through

Functions of the Plasma Membrane

• barrier

• selectivity

• molecular recognition

• export of wastes and cell products

• import of nutrients

• change in response to its environment

Structure of the Plasma Membrane

Outsideof cell

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Insideof cell(cytoplasm)

composed of the phospholipid bilayer.Cellular Structure and Function

phospholipid molecule is made of a glycerol backbone, 2 fatty acid chains, and a phosphate group.

Structure of the Plasma Membrane

• made of 2 layers of phospholipid molecules (bilayer)

• protein molecules are embedded in the lipid bilayers

Phospholipids

• have polar, water soluble heads

• have long nonpolar, water insoluble tails

• phospholipids are not chemically bonded to each other and are free to move about

Phospholipid Molecule

Fluid Mosaic Model

• Fluid because the membrane is flexible (phospholipids & proteins move) free to move sideways within the membrane.

• Proteins create a pattern (mosaic).

Polar/Non Polar Molecules

• Most cells have a watery environment on the inside and outside.

• Polar phosphate group allows the membrane to interact with its environment (water is polar).

• Fatty acid tails (nonpolar) avoid water forming the interior of the membrane.

• Phospholipid heads face the watery environment outside the cell.

Polar/Nonpolar Molecules

• This means that water soluble molecules will not easily move through the membrane because they are stopped by this water-insoluble (phospholipid) layer.

Other Components of Plasma Membrane

• Cholesterol

–Rigid molecules

–helps strengthen & stabilize the phospholipids

–Prevents fatty acid chains from sticking together

Membrane Proteins

Most of the functions of the membrane are carried out by

proteins.

Functions of the Membrane Proteins

• Identify other molecules•determine which particles can pass

across the membrane•move materials through the plasma

membrane•Communicate between a cell and its

environment

Functions of Membrane Proteins

•Act as markers that are recognized by chemicals from both inside and outside the cell. These markers are involved in fighting diseases.

•serve as enzymes •Aids in cell’s internal support

structure

7.3 Structures & Organelles

(pp. 191-200)

2 Types of Eukaryotic Cells

Plant Cell Animal Cell

Cytoplasm

Jelly-like material that fills the space between the nucleus and cell membrane

More than half the volume of a cellImportant chemical reaction occur hereSuspends the organelles

Cytoskeleton

Network of thin, fibrous elements that act as a scaffold to provide support for organelles

Helps maintain cell shape (like tent poles)

Constantly changing structure

Cytoskeleton: composed of

– Microtubules – thin, hollow cylinders made of protein

– Microfilaments – thin, solid protein fibers

Centrioles

Occur in pairsFormed by groups of microtubulesImportant in cell division

Nucleus

manages all cell functions, all organelles

contains the cell’s DNA - master instructions for building proteins

Nucleus

master set of instructions for proteins contained in the chromatin

chromatin-strands of genetic material, DNA

when cell divides, chromatin condenses to form chromosomes

Nuclear Envelope

a double membrane that surrounds the nucleus

has large pores so materials can pass back and forth between the nucleus and the rest of the cell

Nucleolus

an organelle in the nucleus

a region that produces ribosomes which make proteins

Ribosomes

Although not bound by a membrane, they are considered organelles

only job is to make proteins

Endoplasmic Reticulum (ER)

Folded system of membranes that forms a network of interconnected compartments inside the cell

Provides a large surface area

Endoplasmic Reticulum (ER)

Contain enzymes for almost all lipid synthesis

Serve as the site of lipid synthesis in the cell– Rough ER – studded with

ribosomes– Smooth ER – no attached

ribosomes

Smooth & Rough Endoplasmic Reticulum

Smooth ER lacks ribosomes & makes proteins USED In the cell

Rough ER has ribosomes on its surface & makes proteins to EXPORT

Golgi apparatus

Closely stacked flattened

membrane sacs Have a shipping side & a receiving side Receives newly synthesized proteins and lipids

from the ER in vesicles and redistributes them Modifies proteins chemically, then repackages Transport vesicles with modified proteins pinch Transport vesicles with modified proteins pinch

off the endsoff the ends The ‘post office’ of the cell

Transport

vesicle

Vacuole

Membrane bound, temporary storage spaces Store food, enzymes, wastes Contractile vacuole – collects excess water

and pumps it out of the cell Central vacuole – single large vacuole that

stores water in a plant cell

Lysosomes

Contain digestive enzymesDigest excess or worn out cell parts, food

particles, and invading viruses or bacteriaCan fuse with vacuole and dispense contentsExample:

– digestion of a tadpole’s tail– the anterior end of a sperm cell

Mitochondria

“Powerhouse” of the cell Produces energy (ATP) from

glucose Consists of an outer membrane

and a highly folded inner membrane

Numbers vary based on function of cell

Active cells like muscles have more mitochondria

In Animal Cells:In Animal Cells:

Mitochondria

Chloroplasts

Found in green plants

& a few protists Transforms light energy, carbon dioxide and

water into carbohydrates - photosynthesis Contain chlorophyll Has a double membrane Inner membranes arranged in stacks called

grana, look like coins

Chlorophyll

Green pigmentTraps the energy from sunlightGives plants their green color

Plastids

group of organelles that includes chloroplast

Used for storageStore starches, lipids or pigmentsNamed according to their color or

pigmentExample: chlorophyll=chloroplasts

Cell Wall

surrounds the plasma membranemuch thicker than the plasma membranefound in the cells of plants, fungi, most bacteria,

and some protists(not in animal cells)made of cellulose in plants- interwoven fiber

network to protect and gives supportmade of chitin in fungidoes not select which molecules can enter

Cilia

Short, numerousHair-like projectionsBeating movement is coordinated much

like the stadium “wave”Used in locomotion in single-celled

organismsMade of a central pair of microtubules

surrounded by nine additional pairs

Flagella

Longer projectionsWhip-like motionNot as numerous as ciliaUsed in locomotion in single-celled

organismsMade of central pair of microtubules

and surrounded by nine additional pairs

67

Organelles video clip

Similarities between Similarities between plant cells and animal plant cells and animal

cellscellsBoth have a cell membrane surrounding the cytoplasm

Both have a nucleus

Both contain mitochondria

Differences between Differences between plant cells and animal plant cells and animal

cellscellsAnimal cells Plant cells

Relatively smaller in

sizeIrregular shape

No cell wall

Relatively larger in size

Regular shapeCell wall present

71

Animal cells Plant cells

Vacuole small or absent

Glycogen as food storage

Nucleus at the center

Large central vacuole

Starch as food storage

Nucleus near cell wall

Differences between Plant Differences between Plant Cells and Animal CellsCells and Animal Cells

Cellular Organization

UnicellularMulticellular

– Tissue– Organs– Organ system– Organism

7.4 Cellular Transportpp. 201-207

Brownian Motion

• 1827, Robert Brown observed pollen grains suspended in water

• Grains moved constantly in little jerks as if being struck by invisible objects

• He was observing evidence of the random motion of molecules colliding.

Passive Transport

• Passive transport is the movement of particles across membranes by diffusion.

• The cell uses no energy to move the particles.

• Only a few substances are able to pass directly through the phospholipid bilayer in this manner.

• examples; water, lipids, lipid-soluble substances

Diffusion

• Movement of particles from a region of high concentration to an area of low concentration

• The random collisions (Brownian motion) tend to scatter particles of solute and water until they are evenly mixed.

Factors That Affect the Rate of Diffusion

• Concentration

• Temperature

• Pressure

Examples of Diffusion

Diffusion Across a Cell Membrane

• Only molecules of water, oxygen, nitrogen, carbon dioxide, and a few other small nonpolar molecules can diffuse directly across the lipid bilayer.

Diffusion Across a Cell Membrane

• The lipid bilayer makes it difficult for charged ions or polar molecules to pass through by diffusion because they are not attracted to the nonpolar structures of the fatty acid tails.

Dynamic Equilibrium• The condition, in which there is

continuous movement of particles but no overall change in concentration.

• Particles evenlydistributed

Water is equal inside the cell and outside the cell.

Facilitated Diffusion

• The passive transport of materials across the plasma membrane by transport proteins

• Channel (transport) proteins provide openings for particles to pass through.

• examples: sugars, amino acids• Carrier proteins change shape helping

move the particle(s) through the membrane.

Osmosis

• The diffusion of water molecules through a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration.

• Important in maintaining homeostasis

Osmosis Examples

• Strong sugar solution - lower concentration of water

• Weak sugar solution - higher concentration of water

• Organisms are subject to osmosis because they are surrounded by water solutions.

Concentration Gradient

• The difference in concentration of a substance across a space

Osmosis Animation

• Link to animation

Osmosis (out of the cell)

• A cell will lose water by osmosis if it is placed in an environment in which the water concentration is lower than that of the cell contents

• More water is inside the cell

• Therefore, water will move out of the cell.

Osmosis (into the cell)

• A cell will gain water if the water concentration is greater than that of the cell contents.

• More water is outside the cell

• Therefore, water moves in the cell

Isotonic Solution

• A solution in which the concentration of dissolved substances is the same as the concentration inside the cell

• Although water molecules move into and out of the cell, there is no net movement.

• No osmosis occurs.

Isotonic Environment

Hypotonic Solution

• A solution in which the concentration of dissolved substances is lower than the concentration inside the cell.

• Osmosis will cause water to move into the cell.

• The cell swells and its internal pressure increases.

• Pressure that exists in a cell is called turgor pressure.

Hypotonic Environment

Hypertonic Solution

• A solution in which the concentration of dissolved substances is higher than the concentration inside the cell.

• Osmosis will cause water to leave the cell.

Hypertonic Environment

Osmosis Simulation

View Internet Site

Key to Osmosis

• The key to remember about osmosis is that water flows from the solution with the lower solute concentration into the solution with higher solute concentration.

Animal Cells in aHypertonic Solution

• Animal cells placed in a hypertonic solution will shrivel

because of decreased pressure in the cells.

Effects of a Hypertonic Solution• You do not salt meat before cooking

because the salt forms a hypertonic solution on the meat’s surface and the water inside the meat’s cells diffuses out. The result is cooked meat that is dry and tough.

Plant Cells in a Hypertonic Solution

• If a plant cell is placed in a hypertonic environment, it will lose water and shrink away from the cell wall.

• The resulting loss of turgor pressure is called plasmolysis.

• This process will cause the plant to wilt.

Active Transport

• Movement of molecules from an area of lesser concentration to an area of higher concentration

• The cell must use energy.

• Requires moving materials against a concentration gradient

• examples: nutrients such as minerals that are scarce in the environment

How Active Transport Occurs• A transport protein binds with a particle of

the substances to be transported.• Chemical energy is used to change the

shape of the protein so that the particle to be moved is released on the other side of the membrane.

• Once the particle is released, the protein’s original shape is restored.

• Particles can be moved in or out of the cell.

Na+/K+ ATPase Pump

• Found in plasma membrane in animals

• Maintains level of Na+/K+ inside & outside the cell

• 3 Na+ out and 2 K+ in

Transport of Large Particles

• Endocytosis - the cell surrounds and takes in material from its environment

• does not pass directly through the membrane

• It is engulfed and enclosed by a portion of the cell’s membrane and creates a vacuole.

Transport of Large Particles

• Exocytosis - the expulsion or secretion of materials from a cell– Expel wastes such as indigestible particles– Secrete substances such as hormones

produced by the cell

• Both endocytosis and exocytosis require energy and are forms of active transport.

Types of Transport Proteins

• Channel Proteins– Passive transport – requires NO energy– Provides openings through which small

particles, especially ions diffuse

• Carrier Proteins– Active transport – requires energy– Picks up ions or molecules and carries them

across the membrane to the other side