Unit 2 AP Exam Review

Cell Structure and Function, Organelles

Ribosome

2 Structures and 1 Function

Demonstrates a common ancestry of all known life because it is found in all living organisms and performs the same function

Structure: A large subunit and a small subunit

• The large subunit adds amino acids while the small subunit binds to mRNA.

Function: Protein synthesis

3 types of RNA

messenger RNA (mRNA): Brings genetic information from DNA to ribosomes for protein synthesis

transfer RNA (tRNA): Delivers amino acids to the ribosomes during protein synthesis

ribosomal RNA (rRNA): Crucial part of the ribosome structure, also acts as a ribozymes to catalyze peptide bond formation during translation

Other types include snRNA(involved in splicing during RNA processing), miRNA(control gene expression) and Ribozymes(catalytic activity).

Rough Endoplasmic Reticulum

3 Structures and 3 Functions

Structure: Network of connected cisternae(flattened sacs) and tubules with ribosomes on its surface

• This structure provides a wide surface area for protein synthesis to occur.

Function: Protein synthesis; calcium storage; transport of molecules such as proteins

Relationship between Ribosomes and the Rough ER

Ribosomes are located on the surface of the rough ER. Once proteins are synthesized by the ribosome, they can immediately be modified in the rough ER, packaged and transported by vesicles.

Smooth Endoplasmic Reticulum

2 Structures and 5 Functions

Structure: Network of tubules and vesicles

• This structure provides a wide surface area for metabolic processes like lipid synthesis.

Function: Lipid synthesis, detoxification, transport of products

• Calcium storage, carbohydrate metabolism

Overall 3 Functions of the Endoplasmic Reticulum

Provides mechanical support by forming a network of membranes to maintain the shape of the cell and for metabolic processes

Aids protein synthesis by providing a wide surface for ribosomes and transporting and modifying proteins

Helps with intracellular transport by packaging lipids and proteins in vesicles for delivery to other cellular compartments

Golgi Body/Complex/Apparatus

2 Structures and 3 Functions

Structure: A series of cisternae(flattened, membrane-bound sacs) stacked together, with vesicles budding off the cisternae

• The cisternae provide separate departments for the processing, sorting and packaging of proteins and lipids. They each contain unique enzymes for specific modifications.

Function: Modifies, packages and sorts lipids and proteins from the ER, involved in lysosome formation, synthesizes complex lipids like glycolipids and sphingomyelin

Mitochondria

4 Structures and 5 Functions

Structure: Oval or rod-shaped; double-membrane; inner membrane is folded into cristae; a matrix

• Cristae increase surface area for cellular respiration and contain proteins involved in the electron transport chain.

• The matrix is where the Krebs cycle(citric acid cycle) occurs(for prokaryotes, it’s the cytoplasm).

• The outer membrane is freely permeable while the inner membrane only allows very small molecules to pass through.

• The intermembrane space provides a barrier to maintain the proton gradient, which drives ATP synthesis, and serves as a platform for electron transport chain to take place.

Function: ATP synthesis(energy production); Involved in cell signaling, calcium storage, heat production, and cell growth and death

Lysosome

3 Structures and 7 Functions

Formed from the Golgi Apparatus

Structure: Spherical, membrane-bound, contains hydrolytic enzymes, maintains an acidic pH for the enzymes

Function: Aids in intracellular digestion by breaking down cellular waste, damaged organelles, and ingested materials (ie bacteria); recycles organic materials to provide building blocks for new molecules; aids apoptosis by releasing lysosomal proteases (digestive enzymes) into the cytosol (this also happens in autolysis)

• Phagocytosis: Engulfs and digests external materials like pathogens

• Also involved in plasma membrane repair, cell signaling and energy metabolism

Vacuoles

1 Structure and 5 Functions

Can be formed from the fusion of multiple membrane vesicles

Structure: Membrane-bound sac that is typically filled with fluid

• Plants cells have one large vacuole, while animal cells have numerous smaller vacuoles.

Function: Storage(of macromolecules, water, nutrients, ions, salts, waste products), waste disposal(plays a role in macromolecule degradation through enzymes in the vacuole), endocytosis and exocytosis, osmoregulation

3 Different Types of Vacuoles

Central Vacuoles are the large vacuoles in plant cells that maintain cell structure and turgor pressure by storing water and solutes.

Food Vacuoles, found in some protists and phagocytic cells, store and digest food particles by engulfing food particles and then fusing with lysosomes for digestion.

Contractile Vacuoles are specialized vacuoles in some protists that are responsible for osmoregulation by pumping out excess water.

Chloroplast

5 Structures and 1 Function

Structure: Double-membrane; stroma(inner-membrane space) containing enzymes, DNA and ribosomes; thylakoids, flattened sacs that stack to form the grana; the thylakoid membrane embedded with chlorophyll, other pigments and the electron transport chain; the stroma lamellae connecting the grana stacks

• The grana(thylakoids) is where light-dependent reactions occur.

• The stroma is where light-independent(Calvin cycle) reactions occur and synthesize ATP.

• The thylakoid captures energy by hosting light-dependent reactions and stores it in the form of ATP and NADPH. Its chlorophyll-embedded membrane absorbs light energy.

Function: Photosynthesis

Cellular Respiration vs Photosynthesis

Electron Transport Chain and ATP Synthesis

Cell Respiration: For plants and animals, the ETC takes place in the mitochondrial inner membrane space. ATP synthesis primarily occurs in the matrix.

Photosynthesis: The ETC takes place in the thylakoid membrane of the chloroplasts. ATP synthesis occurs within the thylakoid membrane.

Surface Area to Volume Ratio

Formulas are provided on the AP reference sheet.

This ratio limits the size of cells. If the cell is too large, its volume cannot be sustained by the nutrients absorbed by the smaller surface area.

Therefore, a higher ratio(larger surface area, smaller volume) is more favorable for cells. The higher the ratio of surface area to volume, the more efficient the cell.

Large surface area allows higher rates of heat exchange.

Projections called villi and microvilli increase surface area.

2 Examples of Specialized Surfaces for Nutrient Exchange

Alveoli in the lungs are specialized surfaces for gas exchange of oxygen and carbon dioxide between the lungs and blood in the capillaries.

Stomata in plants are also specialized surfaces for gas exchange of oxygen and carbon dioxide between the plant and the atmosphere.

2 Strategies to Obtain Nutrients and Eliminate Wastes

Autotrophs, such as plants, use photosynthesis to create their own food.

Animals eliminate wastes through excretion.

The Cell Membrane

Found enclosing the cell, separating internal and external environments, and around certain organelles. Found beneath the cell wall in plants.

Fluid Mosaic Model: The cell(plasma) membrane is a flexible lipid bilayer with proteins, lipids and carbohydrates floating in it.

Selective Permeability: Small, nonpolar molecules(oxygen, carbon dioxide) can pass through but large, polar molecules (glucose, proteins, nucleic acids) can not.

• Transport proteins will transport specific molecules across the membrane.

Bulk Transport: When a vesicle fuses with the membrane, releasing its contents inside or outside the cell. This is used to transport molecules like hormones and waste products.

4 Components of the Cell Membrane

Phospholipids provides structural support and flexibility by forming a lipid bilayer, with hydrophilic heads facing outwards and hydrophobic tails facing inwards. This allows controlled passage of substances in and out of the cell.

Proteins are embedded in the membrane linked to lipids in the membrane. They facilitate the movement of molecules across the membrane as channels, carriers and pumps.

Carbohydrates link with proteins and lipids to form glycoproteins and glycolipids on the outer surface of the membrane.

• Glycoproteins allow cells recognition, signaling and immune response.

• Glycolipids play a role in cell-to-cell communication.

Cholesterol (or sterols in plants, fungi and bacteria) maintain the fluidity and structure of the membrane.

3 Types of Membrane Proteins

Channel Proteins: Pores that allow passive transport

Carrier Proteins: Bind to molecules and undergo conformational changes to transport them across membranes

Protein Pumps: Carrier Proteins that use energy like ATP to actively transport molecules against the concentration gradient

5 Functions of Membrane Proteins

• Transport

• Signaling and Cell-to-cell communication

• Structural support to maintain cell shape

• Enzymatic activity

• Maintain the internal environment of the cell by regulating what enters and exits via channels and pumps

Cell Wall

3 Organisms, 2 Functions, Components

Plant cells, fungi and most prokaryotes have a cell wall, which encloses around the cell membrane.

Function: Maintains cell structure, acting as a rigid outer layer, and preventing the cell from bursting when water flows in from a hypotonic solution

• Plasmodesmata, channels connecting the cytoplasm of adjacent cells, allow materials to pass through the cell wall.

Components in Plants: Cellulose(a carbohydrate), hemicellulose, pectin, and sometimes lignin

Components in Fungi: Chitin, glycans and glycoproteins

Components in Prokaryotes: Peptidoglycan, a molecule composed of sugar and amino acid chains

Passive Transport

2 Examples

The movement of molecules along a concentration gradient, from high to low concentration

Osmosis is the passive movement of water. Diffusion is the movement of molecules with the concentration gradient(high to low concentrations).

Active Transport

Two Examples

The movement of molecules against the concentration gradient, which requires energy usually in the form of ATP

The Na+/K+ (Sodium-potassium) pump moves sodium ions out of cells and potassium ions into cells, creating a concentration gradient. This powers the active transport of glucose uptake, using the sodium gradient to move glucose into cells.

Exocytosis and 3 Types of Endocytosis

Exocytosis: Active transport that moves large molecules out of cells using internal vesicles that fuse with the plasma membrane

• Hormones are one example of materials that require exocytosis.

Endocytosis: Active transport that large molecules into cells

• Phagocytosis: cells take in large particles

  • Usually food material, which is digested by enzymes from the lysosomes

• Pinocytosis: cells take in large amounts of liquid

• Receptor-mediated endocytosis: receptors on the cell captures passing molecules

• Viruses are one example of materials that requires endocytosis.

Concentration Gradient

An area of high concentration and low concentration, maintained by active transport and metabolic processes that consume molecules on one side

Facilitated Diffusion

Large polar molecules, charged molecules and ions diffuse through the membrane via carrier proteins and protein channels.

• Ion passage can create or alter electric charge differences across membranes.

Small amounts of water can diffuse through the membrane but large amounts require aquaporins(channel proteins).

ATPase

Enzymes that catalyze the hydrolysis of ATP into ADP and inorganic phosphate, releasing energy for processes

Na+/K+ ATPase actively transports Na+ ions out of the cell and K+ ions in, contributing to the resting membrane potential.

Tonicity

A hypotonic solution has a lower concentration than the cell.

A hypertonic solution has a higher concentration than the cell.

An isotonic solution has equal concentration (or water pressure) as the cell.

• Water will flow from hypotonic(low-concentration) environments to hypertonic(high-concentration) environments. The flow of water in or out can cause a cell to bloat or shrink.

Water Potential

The difference in potential energy between a given water sample and pure water

Water will flow from a cell with higher water potential to a cell with lower water potential.

Water potential adds solute potential and pressure potential. The formula for calculating water potential is on the AP reference sheet.

Homeostasis and Osmoregulation

Homeostasis is maintaining stability in the cell.

Osmoregulation is regulating water and water pressure to maintain homeostasis. Cells complete osmoregulation through osmosis and semi-permeable membranes. Organisms complete osmoregulation through salt intake, water intake and exertion.

Simple Diffusion vs Facilitated Diffusion

Both are type of passive transport, moving molecules along the concentration gradient without requiring energy.

Simple Diffusion: Molecules move directly across the lipid bilayer

Facilitated Diffusion: Molecules move across the membrane with the help of transmembrane proteins (channel or carrier proteins)

Compartmentalization

The membrane of organelles ensures efficient and controlled function by creating distinct environments for specific enzymatic reactions or transport mechanisms to occur.

• For example, active transport and endocytosis, both require compartmentalization.

• The multiple membranes and sacs found in the Golgi allow compartmentalization of different reactions. The thylakoids membrane also requires compartmentalization for the proton gradients that are essential to ATP synthesis.

Prokaryotic vs Eukaryotic Cells

3 Similarities and 3 Differences

Both have a plasma membrane and cytoplasm, use DNA as their genetic material, and have ribosomes for protein synthesis.

Eukaryotes have a nucleus, Prokaryotes don’t.

Prokaryotic DNA is typically circular while eukaryotic DNA is linear and organized into chromosomes.

Eukaryotes have membrane-bound organelles like mitochondria, ER, and Golgi Apparatus, while prokaryotes don’t.

Additionally, prokaryotes are always unicellular and are smaller.

Endosymbiotic Theory

Proposes that eukaryotic organelles like mitochondria and chloroplasts originated as free-living prokaryotic cells that were engulfed by larger cells, forming a symbiotic relationship that led to their integration into the host cell.

• Suggests that mitochondria evolved from aerobic bacteria and chloroplasts evolved from cyanobacteria

Endosymbiotic Theory: 3 Similarities between Mitochondria and the Ancestral Species

1. Both reproduce through binary fission

2. Mitochondria have circular DNA similar to that of prokaryotes

3. Similar size and shape

Endosymbiotic Theory: 3 Similarities between Chloroplasts and the Ancestral Species

1. Similar ribosomes

2. Chloroplasts have circular DNA similar to that of cyanobacteria

3. Similar membranes

Endosymbiotic Theory: Chloroplasts vs Mitochondria

Mitochondria are believed to have evolved before chloroplasts.

• Mitochondria are found in all eukaryotic cells while chloroplasts are only found in plants and algae.