AP Bio Unit 2

Cell Theory

• Every living organism is made of one or more cells.

• The cell is the structural and functional unit of all organisms, it is the smallest unit of life, individually alive even as part of a multicellular organism.

• All living cells arise by division of pre-existing cells.

• Cells contain hereditary material, which they pass to their offspring during division.

Prokaryotic Cells

Made up of only

1. plasma membrane - cell barrier

2. cytosol/cytoplasm - fluid portion of the cell

3. genetic material (chromosomes)

4. Ribosomes - builds proteins

**see on the outside vs on the inside

Eukaryotic Cells

• compartmentalize their functions (organelles)

• isolate specialized environments (pH, molecules)

• increase internal surface area for reactions

  • Surface area = more ribosomes = more protein

Autotrophic

characteristic of eukaryotic cells - “plant like”

Heterotrophic

characteristic of eukaryotic cells - “animal like”

Endomembrane System

efficiently coordinates the sending of proteins from ribosomes to their destination

Nucleus

Permanently stores DNA

Hosts DNA synthesis (replication)

Hosts RNA synthesis (transcription)

Nucleolus

compartment of nucleus that makes ribosomes

Ribosomes

The site of translation for protein synthesis - where proteins are assembled from amino acid monomers

• free ribosomes make cytoplasmic proteins

• Bound ribosomes (on rough ER) make membrane and excretory proteins

Rough ER

compartmentalizes cell for protein synthesis

Smooth ER

• package proteins sent from Rough ER into vesicles and send them to Golgi Apparatus

• other proteins stay in smooth ER to become enzymes that break down macromolecules or poisons (detoxification)

• smooth ER also makes phospholipids for cell membrane

Golgi Apparatus

• make final touches

• send finished products to cell membrane to be excreted out of the cell

  • vesicles can also be sent to peroxisomes or lysosomes

Vesicles

small membraneous sacs that store materials or transport/secrete materials around/out of the cell

Secretory Vesicles

fuse with the cell membrane to deliver membrane proteins or to release secretory proteins

Vacuoles

larger vesicles that function as storage for food, water, or waste (type of vesicle)

Large Central Vacuole

found in plant cells

stores water and exerts an outward force (turgor pressure) on the cell wall to provide rigidity and structure to plants

Contractile Vacuoles

dispels excess water - prevents a single-celled organism from absorbing too much water and dying

Lysosomes

RECYLCLE

• produced by golgi apparatus

• 50+ kinds of hydrolytic enzymes

• digests old cell parts + large food molecules

• only in animal cells

Peroxisomes

• formed by fusing vesicles from the mitochondria and rough ER

• mostly in animals’ liver

• in plants, they’re found in seeds and help germinate

• found in nearly all eukaryotic cells

Mitochondria

Eukaryotic organelle that makes the energy molecule ATP through aerobic respiration

• inner membrane is folded (folds are called cristae) because it needs more surface area to maximize the amount of chemical reactions occurring

  • more surface area = more ATP being made

• very innermost area = matrix

  • stores enzymes, proteins, and DNA

Chloroplasts

• function in photosynthesis

• contains the pigment chlorophyll

• thykaloids = flat green pancakes

• grana = stacks of thykaloids

• stroma = fluid surrounding thykaloids

Cytoskeleton

• a network of structural proteins throughout the cytoplasm

• parts of the cytoskeleton reinforce, organize, and move cell structures - can even move the whole cell

• cilia and flagella are extensions that allow for mobility

• Motor proteins use cytoskeleton as highways and drag important stuff with it

Cell Walls

cross-linked networks of structural polysaccharides

• plant walls are made of cellulose

• fungal walls are made of chitin

• bacterial walls are made of peptidoglycan

Extracellular Matrix

networks of connective proteins (like collagen) outside the cell membrane

Tight Junctions

seals adjacent cells to block passage of anything between the cells

Adhesive Junction

provide strong mechanical attachment and structural stability to tissues that endure stretching or abrasive forces

• doesn’t necessarily block anything

Gap Junction

allow direct chemical and electrical communication by forming hollow cylindrical channels that let ions and small molecules pass directly from one cell to another

Cell Size

• bigger cell size = more surface area = more substances can cross the membrane

• efficient transport requires high surface area to volume ratio

  • Too large → cannot exchange matter efficiently (nutrients can’t travel inside the cell fast enough, or wastes can’t be transported out fast enough). 

  • Too small → not enough materials can fit inside, or heat and nutrients diffuse out too fast to keep the cell alive

  • Multicellular organisms maintain large volumes by increasing their surface area with many individual cells

  • Cell Shape - Large cells that need more interaction with their environment will either stretch out, or form convolutions like microvilli to increase surface area. Organelles like chloroplasts, ER, Golgi Apparatus, and mitochondria do this too, as their function depends on chemical reactions occurring on cell membrane surfaces.

Cell Membrane Structure

made of two layers of phospholipids

• phospholipids are amphipathic w/ polar (hydrophilic) and nonpolar (hydrophobic) regions

• they also make the cell membrane semipermeable

Fluid Mosaic Model

• Phospholipids drift and move like a fluid- they can flip sides or travel to different locations within the membrane. 

• Mosaic- Made of many proteins, glycoproteins, steroids, and cholesterol molecules embedded in the phospholipids. 

Membrane Proteins

• Peripheral proteins temporarily attach to the lipid bilayer’s surfaces by interactions with lipids or other proteins. These can be signaling or communication molecules, like insulin and hormones. 

• Integral proteins permanently attach to the cell membrane.

  • Transmembrane proteins are embedded all the way through the plasma membrane, and have ends sticking outside and inside the cell. Mostly used for transport or cellular communication. 

Cholesterol

molecules embedded within the bilayer that help to maintain membrane fluidity over a range of temperatures

Cellular Transport

movement of molecules across a cell membrane (passive and active)

Simple Diffusion

• type of passive transport

• small, uncharged molecules pass through phospholipids

  • osmosis is the diffusion of water

Facilitated Diffusion

• type of passive transport

• large or charged molecules pass through membrane proteins

5 Factors for Rate of Diffusion

1. size of molecules (larger molecules diffuse slower)

2. temperature (occurs faster in higher temperatures)

3. steepness of the concentration gradient (more concentrated areas will diffuse out faster)

4. charge of molecules involved, and the environment diffusing in

5. pressure

Selective Permeability

the ability of a cell membrane to control which substances and how much enter or leave the cell

• allows the cell to maintain a difference between its internal environment and extracellular fluid

• supplies the cell with nutrients, removes wastes, and maintains volume and pH

• small molecules (polar or nonpolar) cross easily

• hydrophobic core prevents passage of ions and large polar molecules (require facilitated diffusion)

Active Transport

• when molecules move from low to high concentrations

• “concentrates” molecules in certain areas

• requires energy from ATP

• counteracts diffusion by creating concentration gradients

Protein Pumps

activated when they are phosphorylated (takes a phosphate from ATP) - changes the protein’s shape

Bulk Transport

Cells can ingest (endocytosis) or secrete (exocytosis) large particles and/or large amounts of particles

• ingesting food is phagocytosis

• ingesting liquid is pinocytosis

• requires energy to move vesicles out and to swallow/create vesicles when taking stuff in

Osmosis

• diffusion of water through phospholipid membrane via simple diffusion

• osmosis also occurs through channel proteins called aquaporins for large amounts of water

• water diffuses via osmosis to the side of the membrane with the highest solute concentration until dynamic equilibrium is reached

Tonicity (animal cells)

• Isotonic to the cell with the same solute concentration on either side. Water moves into and out of the cell at equal rates. Happy cells!

• Hypotonic to the cell with the solution with a lower solute concentration outside the cell, so water will move INTO the cell to dilute the solutes there. Cells can swell, lyse (burst), and die. 

  • if the cell is hypotonic, it has a higher concentration than its environment so water comes in

• Hypertonic to the cell with the solution with a higher solute concentration outside the cell, so water moves OUT of the cell in an attempt to dilute the solutes there. Cells become shriveled, dehydrated, and can die. 

  • if the cell is hypertonic, it has a lower concentration than its environment so water goes out

Tonicity (plant cells)

• Hypotonic- Turgid (turgor pressure normal), plant retains shape. The cell wall prevents the cell from lysing. 

  • HOWEVER- it is possible to over-water plants enough where turgor pressure overcomes the structure of the cell wall, and will lyse and cause the plant to get mushy and die. Especially true of cacti. 

• Isotonic- Vacuole no longer exerts enough turgor pressure, plant begins to wilt. 

• Hypertonic- plant cell becomes plasmolyzed and cytoplasm begins to dry up along with vacuole. Plant is now in crisis mode and may soon die. 

Turgor Pressure

outward pressure exerted on plant cell walls by the large central vacuole - gives plants their structure/shape

Water Potential

• Water will move from an area of:

  • higher ψ to lower ψ (more negative ψ)

  • high water potential = more free water

  • low water potential = less free water

  • adding solute lowers water potential

  • low water potential = more negative

  • high water potential = closer to 0