AP Biology Unit 2: Cell Structure and Function

Which is more effective, a small cell or a large cell?

A small cell

Why are small cells more effective?

They require less nutrients than larger cells and less energy to transport things across the cell.

Function of plasma membrane

Form the boundary of a cell

Types of cells plasma membrane is found in

Both Prokaryotes and Eukaryotes.

Features of the Plasma Membrane

• Made of a phospholipid bilayer

• Heads: Hydrophilic

• Tails: Hydrophobic

• Fluid-mosaic model: very flexible and contains multiple proteins and other molecules

• Glycoproteins + glycolipids are attached to the membrane. Helps with signaling and attachment

Selective Permeability

Some things pass through easily while others may not cross or may need a special transport protein to cross

Selective Permeability is from

The structure. Hydrophobic and hydrophilic lipids

Molecules that pass through the membrane:

Small, non polar molecules Ex: Hydrocarbons, CO2, O2, and N2

Molecules that pass through the membrane w/ a transport protein:

Polar, large molecules and ions Ex: Sugars and Water

Passive Transport

Type of transport that DOESN’T require energy

Passive Transport types:

• Diffusion

• Osmosis

• Facilitated Diffusion

Passive Transport Diffusion

Movement from high to low concentration

Passive Transport Osmosis

movement of WATER from a high to low concentration

Passive Transport Facilitated Diffusion

Movement from high to low concentration THROUGH A PROTEIN

Channel Protein

Protein that provides a channel for molecules and ions to pass through to avoid the hydrophobic center. Looks like a straw

Carrier Proteins

Changes shapes to allow the flow of molecules through the concentration gradient

Active Transport

Type of transport through the membrane that requires energy (ATP).

Reasons for active transport

• Molecules need to move against the concentration gradient (low to high)

• Too big to pass through on their own

Types of Active Transport

• Protein pumps

• endocytosis

• ecocytosis

Active Transport Protein Pumps

Protein uses ATP to push molecules through the membrane

Active Transport Endocytosis

Moves larger molecules into the cell via a vesicle

• phagocytosis

• Pinocytosis

• Receptor-mediated endocytosis

Active Transport Exocytosis

Moves large molecules out of the cell via a vesicle

Hypertonic

Water goes OUT of the cell. Causes cell to shrink and shrivel

Hypotonic

Water comes INTO the cell. Causes cell to grow and expand

Isotonic

equal amount of water going in and out of the cell

Prokaryotes

• No nucleus

• Bacteria and Archaea

• Smaller in size

Eukaryotes

• Nucleus

• Cytoplasm has cytosol and membrane-bound organelles

• Protists, fungi, animals, and plants

Every Cell has these 4 things:

1. Bound by a plasma membrane

2. Contain cytosol

3. Contain chromosomes

4. Contain ribosomes

Cytoplasm

The fluid, the structures, and the machinery within the cell's membrane

Cytosol

Just the fluid where everything else floats

Plant v. Animal Cells

Plant:

• Chloroplasts

• Central vacuole

• Cell wall

• Plasmodesmata

Animal:

• Lysosomes

• Centrosomes

• Flagella

Nucleus

Contains chromosomes (genetic information)

• Enclosed by nuclear envelope (Double membrane)

Has pores

• Pores regulate the entry and exit of materials from the cell

The Nucleus’s nucleolus

Region of the nucleus where rRNA is synthesized

• rRNA is combined with proteins to form large and small subunits of ribosomes

Subunits exit via nuclear pores—> Assemble into ribosomes

• Ribosomes translate messages found on mRNA into the primary structure of polypeptides

Ribosomes

Comprised of ribosomal RNA and protein

Function: synthesize proteins

Ribosome locations:

1. Cytosol 

   • Proteins produced here generally function only within the cytosol (i.e. enzymes)

   • Known as “free ribosomes”

2. Bound to the ER or nuclear envelope

   • Proteins produced here can be secreted from the cell

   • Leave via transport vesicles

Endoplasmic Reticulum (ER)

A network of membranous sacs and tubes

Functions:

• Synthesizes membranes

• Compartmentalize the cell to keep proteins formed in the rough ER separate from those of free ribosomes

Two types rough and smooth

Rough ER

Contains ribosomes bound to the ER membrane

Smooth ER

Contains no ribosomes and synthesizes lipids, metabolizes carbohydrates, and detoxifies the cell

Golgi Complex

Contains flattened membranous sacs called cisternae

• Separate the sacs from the cytosol

• Each cisternae is not connected

• Has directionality

Directionality of Golgi Complex

Cis face:

• Receives vesicles from the ER

Trans face:

• Sends vesicles back out into cytosol to other locations or to the plasma membrane for secretion

Golgi Complex Functions

• Receives transport vesicles with materials from the ER

• Modifies the materials: Ensures newly formed proteins are folded correctly or modified correctly

• Sorts the materials

• Adds molecular tags

• Packages materials into new transport vesicles that exit the membrane via exocytosis

Lysosomes

Membranous sac with hydrolytic enzymes

Function:

• Hydrolyzes macromolecules in animal cells

• Autophagy: lysosomes can recycle their own cell’s organic materials. Allows the cell to renew itself

Lysosomes: Peroxisomes

Similar to lysosomes and they are membrane bound metabolic compartment 

• Catalyze reactions that produce H₂O₂

• Enzymes in peroxisomes then break down H₂O₂ to water

Vacuoles Types

Food vacuole

• Form via phagocytosis (cell eating) and then are digested by lysosomes

Contractile vacuole

• Maintain water levels in cells

Central vacuole

• Found in plants

• Contains inorganic ions and water

• Important for turgor pressure

Mitochondria

Site of cellular respiration

Structure of the double membrane:

• Outer membrane is smooth

• Inner membrane has folds called cristae —> Divides the mitochondria into two internal compartments and increases the surface area

The Membranes of the Mitochondria

1. Intermembrane: space between inner and outer membrane

2. Mitochondrial matrix: enclosed by inner membrane

   • Contains: Enzymes that catalyze cellular respiration and produce ATP and Mitochondrial DNA