Cell Structures

Ms. KlinkhachornSeptember 12, 2011

AP Biology

Peroxisomes

• Location: All over• Function: chemical

reactions for your cells– Produce hydrogen

peroxide – Examples: • Breakdown alcohol• Bread down fatty acids

Cytoskeleton

• Location: running throughout cytoplasm in a network

• Function: Gives support, allows movement, and helps regulate some chemical reactions

• Three types of fibers make it up:– Microtubules– Microfilaments– Intermediate filaments

Microtubules

• Help with cell division• Shape and support the cell• Make up cilia and flagella

Microfilaments

• Smaller than microtubules • can be involved with movement and support

Intermediate Filaments

• microfilaments < intermediate < microtubules• Help permanently fix things in the cell– Maintain shape– Fix position of organelles

Centrosomes

• Location: near the nucleus until cell division• Function: area that microtubules grow out of– contain centrioles in animal cells

Centrosomes

Flagella and Cilia

• Made of microtubules• Function: Movement of cells – Cilia also help to move fluid over tissue

Flagella and Cilia

Extracellular Matrix (ECM)

• Location: Just outside the cell membrane• Function: Helps to strengthen tissue, helps

transmit stimuli into cells

Intercellular Junctions

• Tight junctions– Places where cells fuse to make the membranes

water-tight• Desmosomes– Fasten cells together to make them strong sheets

• Gap junctions– Provide channels between cells so that molecules can

pass• Plasmodesmata (Plants only)– Similar to gap junctions in animals

Intercellular Junctions

Intercellular Junctions

Membrane Structure and Function

Cell Membranes

• Also called the plasma membrane• All cells have cell membranes – can be

compared to the skin on our bodies• Thin film – need to stack 8,000 to equal the

thickness of a page

Plasma Membrane

• Barrier for the cell • It is selectively permeable– Some materials go through the membrane a lot

easier than others– Some materials can’t go through at all

• What kind of materials need to be able to go in to the cell? Go out of the cell?

Other Membranes

• Membranes can also surround organelles– These organelles are membrane-bound – Create compartments within the cell itself that

have different environments

• What type of cell has membrane-bound organelles?

• What are some examples of membrane bound organelles?

Cell Membrane – What’s what?

Membrane Composition

• Membrane composition depends on the type of cell and the kind of organelle

• Membranes are made up of the following:– Phospholipids– Proteins– Carbohydrates/glycoproteins– Cholesterol

What’s in a membrane?

How do these parts behave?

• Fluid-Mosaic Model – states that components of the membrane are able to move two dimensionally without restraint– Membranes are fluid/dynamic.

• Mosaic = collage– membranes are composed of a variety of

components

How can we remember this?

• “Sea” of phospholipids – move about freely, just like water

• Proteins are like boats or icebergs – half in the water, half out

Phospholipids

• Type of lipid– 2 fatty acids (lipids)

make up the tail– Phosphate group makes

up the head

• Use the roots to figure out the characteristics:– Hydrophobic, nonpolar

tails– Hydrophilic, polar heads

Phospholipid Bilayer

• The cell membrane is organized into two layers of phospholipids called the phospholipid bilayer

• It’s like a sandwich

Phospholipid Structure

Head

Tails

Cell Membrane Components

Cholesterol

• Found imbedded in the lipid bilayer between phospholipids

• Also has a hydrophobic and hydrophilic end

Not all cholesterol is bad

• Helps stabilize the membrane

• Prevents the membrane from being TOO flexible

• Also prevents the membrane from being TOO stiff

Cell Membrane Components

Carbohydrates/Glycoproteins

• Carbohydrates are made up of sugar molecules– Good energy supply

• Glycoproteins are when these carbs are attached to the proteins– not actually inside the bilayer

Carbohydrate Function

• Help with cell-cell recognition– Cell’s ability to distinguish neighboring cells– Helps cells figure out how to sort into tissues and

organs– Cell recognize each other based on the

carbohydrates on the surface of the cell membrane

Types of Glycoproteins/Glycolipids

• Glyco = Sugar• Glycoproteins: carbs

bonded to proteins• Glycolipids: carbs bonded

to lipids

Examples

Blood Types: A, B, AB, and O Immune System Rejection

Cell Membrane Components

Proteins

• Proteins control the day-to-day functions of an organism

• Functions of membrane proteins:– Transport materials in and out of the cell– Messenger systems/Cell Signaling– Enzyme activity for chemical reactions– Cell Recognition

Proteins

• Two Main Kinds of Protein– Integral Proteins• Penetrate the hydrophobic

core• Can be transmembrane

– Peripheral Proteins• Not imbedded in the

membrane• Sit on the outside

Short Response

• Taken from past AP Free Response Questions

1. A major distinction between prokaryotes and eukaryotes is the presence of membrane-bound organelles in eukaryotes.a) Describe the structure and function of TWO eukaryotic

membrane-bound organelles other than the nucleus.2. Membranes are essential components of all cells.

a) Identify THREE macromolecules that are components of the plasma membrane in a eukaryotic cell and discuss the structure and function of each.

Phospholipid Bilayer - Characteristics

Permeability of the Bilayer

• Hydrophobic molecules can pass through, but hydrophilic molecules can not (at least not easily)– Polar molecules = hydrophilic• Examples: Sugars, charged atoms (K+) and molecules

– Nonpolar molecules = hydrophobic• Examples: oxygen, carbon dioxide

Transport Proteins

• Help materials that are big or hydrophilic pass through the membrane easily– Substance specific• If it’s supposed to translocate water and sugar, it will

only translocate water and sugar

• Two Kinds:– Channel Proteins– Carrier Proteins

Transport Proteins

Efficacy of Transport Proteins

• 3 billion water molecules can move across the membrane using an aquaporin per second

• Glucose moves across the membrane 50,000x faster with a transport protein than by itself

Passive Transport

• Diffusion ACROSS A MEMBRANE– Diffusion = movement of molecules so that they

spread out evenly in an available space • Does NOT require energy or use a transport protein• Once the molecules spread out they are in a state of

equilibrium

• Substances diffuse from a high concentration to a low concentration– They move down their own concentration

gradient

Diffusion of Sugar

Concentration Gradient

Types of Passive Transport

• Simple Diffusion• Facilitated Diffusion• Osmosis

Example: Gas Exchange

Simple Diffusion

Facilitated Diffusion

• Diffusion that requires a transport protein

Osmosis

• Diffusion of water across a selectively permeable membrane (where the solute cannot go through the membrane)

• Water will move from an area of lower solute concentration to an area of higher solute concentration– Wants to balance out the solute concentrations

Osmosis

Hypertonic Solutions

• “Hyper” means “above”• A hypertonic solution has a higher

concentration of solute– This means that water is less concentrated

• A cell placed in a hypertonic solution will SHRINK due to water loss.

Plant Cells in a Hypertonic Solution

Before and After

Hypotonic Solutions

• “Hypo” means “below”• A hypotonic solution has a lower

concentration of solute– This means that water is more concentrated

• A cell placed in a hypotonic solution will SWELL due to water intake.

Isotonic Solutions

• “Iso” means “equal”• An isotonic solution has an equal

concentration of solute• A cell placed in an isotonic solution will remain

unchanged• There will still be movement of water, though

there is NO NET GAIN.

DNA – November 30, 2010

Answer these on the back of your study guide:1. What is diffusion? How is it different from

passive transport?2. What do the word forms “hypo”, “hyper”,

“osmo” and “iso” mean?3. Describe what is happening in the picture.

Water Balance in Animal Cells

• If the cell swells too much, it can burst. – This is called lysis. The cell lyses.

• If the cell shrivels too much, it can die.

Examples (Animal Cell)

Water Balance in Plant Cells• Cells still swell in hypotonic environment, but the

wall is more rigid.– Water uptake makes the cell turgid (firm).

• This is a plant’s healthy state.• If the cell is in an isotonic environment, it is

flaccid (limp)• If the cell is in a hypertonic environment, it

plasmolyzes (a process called plasmolysis)– The cell membrane pulls away from the cell wall as

water is lost– Can cause death.

Examples (Plant Cell)

Saltwater fish – Predict what happens to fish in these environments.

Saltwater Fish

• Saltwater fish are constantly swimming in a hypertonic environment

• Fish are consistently losing water from their bodies

• In order to maintain water balance, the fish have to drink a lot of saltwater and pump salt out of their bodies

Freshwater fish – Predict what happens to fish in these environments.

Freshwater Fish

• Freshwater fish live in a hypotonic environment

• Water is constantly moving into their cells

• These fish pee regularly in order to get rid of this water

Osmoregulation

• Osmoregulation = the control of water balance

• Certain organisms are adapted to deal with this– Sea animals – Paramecium

Paramecium

• Paramecium lives in pond water, which is hypotonic to the cell.

• What effect does the hypotonic environment have on this?

• How might the paramecium adapt?

Contractile Vacuole