AP Biology, Unit 2: Organelles

Organelles

Specialized structures inside of a living cell

Prokaryotic cells

Bacterial cells

Unicellular

Do not have a nucleus/organelles are NOT membrane bound

Eukaryotic cells

Animals, plants, fungi, most algae

Multicellular

Contain a nucleus/membrane-bound organelles

Nucleus

• Found in only Eukaryotic cells

• Protected by a nucleus envelope/double membrane structure, bilayer of lipids, proteins

• Protects DNA/chromosomes and nucleolus

• Produces and assembles ribosomes

Ribosomes

• Found in all cells (Eukaryotic + Prokaryotic)

• Creates the proteins found in all cells

• “Free” ribosomes - synthesize proteins in the cytoplasm; “Membrae-bound” ribosomes - found in the ER, synthesizes proteins inserted into the membrane

Rough ER

• “ER”: Endoplasmic Reticulum

• Makes proteins, transports proteins to the Golgi apparatus

• Flattened sacs covered in ribosomes

• Eukaryotic cells

• Production/folding/quality/protein dispatch

Smooth ER

• Eukaryotic cells

• Lacks ribosomes on its surface

• Lipid and protein synthesis, stores calcium, materials received by the Golgi body

• Network of membranes, interconnected tubes, flattened sacs

Golgi Body

• Eukaryotic cells

• Folded membrane sacs

• “Packaging center” of the cell - receives proteins from the ER and modifies, sorts, and ships them across the cell

• Makes lysosomes, maintains carbs to function

Mitochondria

• “Powerhouse of the cell”

• Eukaryotic

• 2 membranes, inside and out phospholipid bilayer

• Cellular respiration - generates energy needed for the cell to function in the form of ATP

• Folds and changes shape

Lysosomes

• Eukaryotic cells (not found in plants)

• Digests and breaks down macromolecules - digestive enzymes

• Made in the Smooth ER

• Membrane lipid layer

Vacuole

• Found in both cell types but Eukaryotic function differs

• Large central vacuole (small in animals, larger in plants)

• Pumps out excess water, pigments

• Stores water, nutrients, ions, minerals, waste products

Chloroplasts

• Eukaryotic cells

• Converts sunlight energy to chemical energy stored in sugar molecules

• 2 membranes - thylakoids interconnected sacs

• Division of membranes creates 3 “compartments”: thylakoids, stroma, inter-membrane

Cytoplasm

Gelatinous liquid inside of a cell; contains water, salts, molecules

Surface area

The total area of the outside of an object

Volume

How much space a object takes up

Surface Area and Volume in Cells

• Cells need to stay small in order to move resources/waste products in and out more efficiently

• Larger SA:V ratio, happier, smaller cell

SA:V ratio

• As an object grows larger, its amount of surface area relative to its volume decreases, decreasing the SA:V ratio

Maximizing Surface Area in Cells

• villi/microvilli

• Membrane folding

• Hairs/projections

Phospholipid bilayer

• Primally nonpolar because of hydrophobic lipids

• Semi-permeable - some molecules can pass though, others need the help of a protein

What substances can/cannot pass through the phospholipid bilayer?

Ex.

• Ethanol (small, nonpolar) - YES

• Chlorine ions (charged) - NO

• Amino acids (large, nonpolar) - NO

• Glucose (large, polar) - NO

*NO = need a channel protein to pass through

Most gasses can pass through; larger molecules cannot

Necessary Characteristics to Permeate the Cell Membrane

• Criteria #1: small size (larger molecule cannot pass through)

• Criteria #2: nonpolar (polar molecules can pass through but will use protein if able; charged molecules cannot and a protein is necessary)

Channel Proteins

• Control movement of substances across cell membranes

• Hydrophilic core

• Used by larger/charged molecules to pass through

Aquaporins

• Water (small, polar) mostly uses aquaporins - specialized channel proteins

• Water CAN pass through the membrane in small amounts

Phospholipid Bilayer of the Cell Membrane

Cholesterol in the Phospholipid Bilayer

• Regulates membrane fluidity

• Stabilizes cell membrane

Glycoproteins in the Phospholipid Bilayer

• ID tags/cell recognition

• Cell signaling

Peripheral proteins in the Phospholipid Bilayer

• Enzymes

• Structural support

• Cell shape, cell messaging

Glycolipids in the Phospholipid Bilayer

• Cell recognition, signaling

• Stability

Diffusion

• Movement of molecules across the semi-permeable membrane

• H → L

• Without energy

• Increased temperatures excite molecules, causing quicker diffusion

Why do cells needs transport?

• Cell membrane maintains homeostasis by regulating what materials can enter and exit the cell

• Without this monitoring ability, cells would not be able to maintain internal conditions like water balance, nutrient levels, waste removal, etc

Concentration gradient

• Molecules are always in motion

• Where there is a difference in concentration (amount of molecules clustered/concentrated in one area), there is a concentration gradient

• Molecules move from areas of H to L concentration until dynamic equilibrium is reached

Dynamic Equilibrium

• Molecules are “balanced”, evenly spread out

• Molecules are still moving, but there is no net change in concentration

Simple Diffusion

• Movement of small, nonpolar molecules directly across the phospholipid bilayer

• H → L

• Requires no energy

• Larger the concentration gradient, the more diffusion occurs

Passive Transport

• No energy - movement relies on the natural direction of molecules

• H → L concentration

1. Simple diffusion

2. Osmosis (diff. of water)

3. Facilitated diffusion (uses some kind of transport protein)

Osmosis

• Diffusion of WATER across the semi-permeable membrane

• Low solute concentration (High concentration of water) to High solute concentration (Low concentration of water)

• Water always moves towards the higher concentration of solute - concentration of said solute dictates the movement of water (hypotonic, isotonic, hypertonic)

• Does not require energy

Hypotonic

• Water moves INTO the cell

• More water outside of the cell, more solute inside the cell

• Animal cells - cell swells

• Plants cells - turgid (normal)

Isotonic

• Water moves IN and OUT of the cell equally

• Animal cells: no net change (normal)

• Plant cells: flaccid

Hypertonic

• Water moves OUT of the cell

• More water inside, more solute outside

• Animal cells: shrinks

• Plant cells: plasmolyze

Osmoregulation

• Water moves from low solute concentration (low osmolarity) to high solute concentration (high osmolarity)

• Cells monitor the movement of water to maintain a stable balance and to prevent the loss/gain of dangerous amounts

Membrane Potential

• Ions change the electrical balance between the inside and outside of the cell when they pass through protein channels

• Difference in charge is called membrane potential

Facilitated Diffusion

• Movement of large/polar substances across the cell membrane from H → L concentration

• Utilizes transport proteins, but does NOT require energy

1. Channel proteins - hydrophilic tunnels, typically used by charged/polar molecules like ions

2. Carrier proteins - change their shape (conformational change), used by large molecules like sugars and amino acids

3. Aquaporins - specialized channels that transport water

Active Transport

• Materials needs to be transported in and out of the cell membrane against their concentration gradient, from L → H concentration

• This movement requires cellular energy in the form of ATP

• Carried out by carrier proteins in the cell membrane that use energy to change shape and move substances across the membrane

Active Transport vs. Facilitated Diffusion

Active Transport requires ENERGY. Facilitated Diffusion uses PROTEINS.

Ion Movement

• Cells maintain specific ion gradients across their membranes in order to carry out process like electron sing along

• These gradients are maintained by ion pumps: membrane proteins that use ATP to move charged particles

Sodium-Potassium Pump

Uses 1 ATP molecule for every transport cycle

• Moves 3 Na+ ions out of the cell (sodium)

• Moves 2 K+ ions into the cell (potassium)

Creates a charged imbalance (more positive outside, more negative inside) and maintains membrane potential (imp. for nerve/muscle function)

Bulk Transport (Active)

• movement of large molecules (ex. proteins, polysaccharides) or large groups of molecules in and out of the cell

• Requires energy

• Involves processes like vesicle formation and membrane fusion

• Can move molecules against their concentration gradient, but does not have to

Endocytosis

Cell takes materials INTO the cell

• folds plasma membrane inward to form a vesicle

• Engulfs particles too large to pass through membrane proteins

3 types: phagocytosis, pinocytosis, and receptor-mediated endocytosis

Phagocytosis

• “cell eating” - moves outwards to engulf material

• Cell engulfs large solids to bring the material into the cell (form of ENDOcytosis)

Vesicle

• A small sac formed by a membrane and filled with liquid.

• Vesicles inside cells move substances into or out of the cell.

Pinocytosis

• “cell drinking” - membrane pinches inward

• Cell takes in smaller extracellular fluid and solutes into the cell (form of ENDOcytosis)

Receptor-Mediated Endocytosis

Receptors on the cell surface bind certain molecules, triggering vesicle formation and subsequent intake of specific molecules

Exocytosis

• large molecules/large groups of molecules move from inside to OUTSIDE the cell

• Vesicles move to and fuse with the membrane and ejects material into extracellular environment

Cell Compartmentalization

A large amount of organelles benefits Eukaryotes because…

• Prevents interferences of different reactions (digestion vs. synthesis)

• Maintains optimal conditions (Lysosomes and pH)

• Increases surface area → allows for more reactions (Ex. Internal membranes of mitochondria/chloroplasts) increase SA and efficiency)

• Allows for direct movement of materials through cell (Ex. Proteins send to the Golgi body)

Organelles: Eukaryotes vs. Prokaryotes

Eukaryotic cells have membrane-bound organelles

• allows for “micro-environments” inside of the cell (ex. Lysosomes are acidic, but the whole cell is not acidic)

• Complex internal organization, efficient processes

Prokaryotic cells lack internal compartments and organelles, therefore not as efficient

Endosymbiotic Theory

IDEA: How did organelles develop?

• specialized organelles were one free-living prokaryotes that were engulfed by a larger cell

• this theory only applies to mitochondria and chloroplasts, which have unique features that support the Endosymbiotic theory

Unique Features: Supports:

• Double membranes → engulfing event

• Possesses circular DNA → prokaryotic origin

• Bacterial ribosomes → prokaryotic translation machinery

• Divide via binary fission (asexual reproduction) → Independent reproduction

Cell Wall

• Found in plants, fungi, many bacteria

• Structure is primarily carbs (cellulose, chitin, peptoglycan)

• Supports and protects the cell, maintains shape

• Porous (not selective)

• Outside of the cell membrane (most outer later of the cell)