AP Biology - Unit 2 Cell Structure and Function

Original Cell Theory

A. All organisms are made of 1 or more cells

B. Cells are the basic unit of structure & function in a living ogranism

C. New cells come from pre=existing cells (A cell divides producing 2 cells *mitosis!)

Prokaryotes

1. PRO = NO NUCLUES, this means DNA/Genetic Material loose inside the cell)

2. Simple (primitive)

3. No membrane-bound organelles

4. The only membrane is the cell membrane

5. Has ribosomes and cell wall

6. Examples: Bacteria (E. coli, Streptococcus)

Eukaryotes

1. EU = DO/TRUE, has nucleus and membrane-bound organelles

2. Complex

3. Genetic Material (DNA) is inside the nucleus 

4. Evolved from prokaryotic cells

5. Can be Unicellular or Multicellular

6. Examples: plant cells, animals, fungi, protists

Endosymbiotic Theory

an idea by Lynn Margulis, that a long time ago, prokaryotic cells engulfed (the process by which a cell surrounds and takes in particles, other cells, or large molecules from its external environment) other prokaryotic cells by Endocytosis which resulted in the first eukaryotic cells. This theory explains the origin of eukaryotic cells and the origin of certain membrane-bound organelles.

Evidence that supports the endosymbiotic theory

similarities between mitochondria, chloroplasts, and prokaryotes

1. Circular DNA

2. Ribosomes

3. Binary fission (the process where a single-celled organism divides into two, genetically identical daughter cells)

Parts/Features that every cell has

1. Ribosomes

2. Cytoplasm

3. DNA

4. Cell Membrane

5. Basic structure/functional unit of every organisms is either prokaryotic or eukaryotic

6. Only organisms of the domains Bacteria and consist of prokaryotic cells

7. Protists, fungi, animals, and plants all consist of eukaryotic cells in Domain Eukarya

Mitochondria

1. membrane-bound organelles

• outer membrane is smooth

• inner is high convoluted, forming folds called cristae, the inside also creates two Compartments called intermembrane space and mitochondrial matrix)

2. that produces energy (ATP) for the cell; evolved from aerobic Bacteria (survives and grows with oxygen) that were engulfed by a larger prokaryotic cell

Mitochondrial matrix and Cristae

some metabolic steps of cellular respiration are catalyzed in mitochondria matrix, cristae present a large surface area for enzymes that synthesize ATP

Chloroplast

membrane-bound organelle that captures sunlight and uses it to make food for the cell (only plant cells and some protists have this); evolved from endosymbiotic photosynthesis (use the sun for energy) bacteria

Ribosomes

particles made of ribosomal RNA and protein; carrys out protein synthesis in two locations 1). cytoplasm aka cytosol (free ribosomes) 2). outside the endoplasmic reticulum or nuclear envelope (bound ribosomes); uses the info from DNA to make proteins

Nucleus

contains most of the DNA in eukaryotic cells; has a nuclear membrane (envelope and nuclear pores; inside, the DNA and proteins form genetic material called chromatin which condenses to form discrete chromosomes

Nucleolus

inside nucleus, site of ribosomal RNA (rRNA) synthesis

Cell Membrane

selectively or semi-permeable which means it regulates what comes in/out the cell, composed of a double layer of phospholipids with proteins embedded throughout

Membrane-Bound Organelles

1. Endoplasmic reticulum

2. Mitochondria

3. Chloroplasts

4. Golgi

5. Nuclear envelope

6. Lysosomes

7. Vacuoles

Why Organelles?

1. Specialized structures with specialized functions like cilia or flagella for locomotion

2. Containers that partition cell into compartments to create different local environments like separate pH, or concentration of materials; distinct and incompatible functions like lysosome and its digestive enzymes

3. Membranes as sites for chemical reactions: unique combinations of lipids and proteins, embedded enzymes and reaction centers, membranes provide more surface area for reactions like chloroplasts and mitochondria

Smooth Endoplasmic Reticulum

1. Membrane production

2. Many metabolic processes: Synthesis (synthesize lipids like oils, phospholipids, steroids & sex hormones); Hydrolysis (hydrolyze glucogen into glucose in liver; detoxify drugs & poisons in liver via alcohol & barbiturates)

Rough Endoplasmic Reticulum

processes proteins for export out of cell: protein secreting cells, packaged into transport vesicles for export

Membrane ASSEMBLY FAACTORYYY

Build new membrane

• synthesize phospholipids/builds membranes

• ER membrane expands: bud off & transfer to other parts of cell that need membranes

• Ribosomes are where proteins are initially synthesized, the ER is a network where proteins and lipids are processed and transported, and the Golgi apparatus modifies, sorts, and packages these molecules for their final destinations. 

• the rough ER, covered in ribosomes, is the primary site for the synthesis and modification of proteins destined for the cell membrane or export. The smooth ER, lacking ribosomes, focuses on lipid synthesis, steroid production, and detoxification. 

Golgi Apparatus

finishes, sorts, tags, and ships cell proteins like a “UPS shipping department”; ships products in vesicles like membrane sacs or “UPS Trucks”

Lysosome

• membranous sac of hydrolytic enzymes that can digest macromolecules

• lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids

• use enzymes to recycle the cell’s own organelles and macromolecules

Vacuoles (Diverse Maintenance Compartments)

membrane bound storage sacs that serve multiple purposes

1. food vacuoles are formed by engulfing food

2. contractile vacuoles are found in many freshwater protists, and pump excess water out of cells

3. central vacuoles are found in many mature plant cells, hold organic compounds and water

4. In plant cells, it takes up a lottttt of space

Mitochondria and Chloroplasts change energy from one form to another

1. not part of the endomembrane system

2. has double membranes

3. have proteins made by free ribosomes

4. contains their own DNA

Site of cellular respirations aka a metabolic process

Mitochondria since it generates ATP

Sites of photosynthesis and only found in plants and algae

Chloroplasts

Peroxisomes

oxidative organelles, specialized metabolic Compartments bounded by a single membrane, produce hydrogen peroxide and converts it into water, oxygen is used to break down different types of molecules

More about chloroplasts and how they capture light energy

1. member of a family of organelles called plastids

2. chloroplasts contain the chlorophyll (green pigment), and enzymes & other molecules that function in photosynthesis

3. found in leaves and other green organs of plants and algae

4. structure includes, thlykoids and membranous sacs that are stacked to form granum, and stroma aka internal fluid

Centrosomes

not in plant cells

plastids

not in animal cells, is in plant

Fluid Mosaic Model

fluid: membrane held together by weak interactions; mosaic: phospholipids, proteins, carbs

carbohydrates

1. cell-to-cell recognition

2. glycolipids, glycoproteins

3. ex, blood transfusions are type-specfic

Phospholipids

1. bilayer

2. amphipathic = hydrophilic head, hydrophobic tail

3. hydrophobic barrier: keeps hydrophilic molecules out

Membrane fluidity

1. low temps: phospholipids w/ unsaturated tails (kinks prevent close packing)

2. High temps: increase phospholipid movement

3. cholesterol resists changes

• adds firmness and integrity to cell membrane

• prevents it from becoming overly fluid or overly firm

• cellular membranes are fluid mosaics if lipids and proteins that are continuously moving in the bilayer

selective permeability

• small molecules (polar or no polar) cross the lipid bilayer easily (hydrocarbons, hydrophobic molecules, CO2, O2)

• hydrophobic core prevents passage of ions, large polar molcules (this is where proteins come in)

membrane

a collage of different proteins embedded in the fluid matrix of the lipid bilayer, proteins determine most of the membrane’s specific functions

Peripheral proteins

bound to surface of membrane, extracellular/cytoplasmic sides of membrane, NOT embedded, held in place by cytoskeleton or ECM, provides stronger frame work

integral proteins

penetrate the hydrophobic core, the ones that span the membrane are called transmembrane proteins, embedded in membrane, transmembrane with hydrophilic heads/tails and hydrophobic middles

6 major functions of membrane proteins

1. transport

2. enzymatic activity

3. signal transduction

4. cell-cell recognition

5. intercellular joining

6. attachment to the cytoskeleton and extracellular matrix (ECM)

Transport proteins

concentration gradient (high to low?), diffusion of lipid-soluble substances, passive transport of water-soluble substances, active transport using ATP

Plants

1. has cell wall that cover their plasma membranes

2. extracellular structure (not found in animal)

• provides shape/structure, protection, regulation of water intake

3. comprised of cellulose

4. thicker than plasma membranes

5. contain plasmodesmata: hole-like structures in the cell wall filled with fluid that connect adjacent cells

Cell Size and Scale

1. most cells are between 2µm and 200µm

2. A micrometer is 1 millionth of a meter!

3. Too small to be seen with naked eye 

Limits on cell size

1. Cellular Metabolism 

   • Diffusion -Movement of molecules from higher

         concentration to lower concentration

   • A cell must be able to take in nutrients and take out waste

   • A cell 20 cm would require months for nutrients to get to the center 

   • dissipate thermal energy (means to separate kinda)

2. Surface Area to Volume Ratio

   •   Volume increase more rapidly than surface area.

   •   When cell size doubles, the cell has 8x as much volume, but only 4x as much surface area

   • Small cells have a greater surface area relative to volume

   
   

Cell size rules

• must be small to maintain a large surface area to volume ratio

• Large S.A. allows ↑ rates of chemical exchange between cell and environment

cell facts

1. tend to be small

• Small cells have a high SA:V ratio

• Optimizes exchange of materials at the plasma membrane

2. Larger cells have a lower SA:V ratio

• Lose efficiency exchanging materials

• The cellular demand for resources increases

• Rate of heat exchange decreases

what if cell is too fat (big)

it can:

1. Have a long thin shape

2. Fold the surface membrane

3. Divide

surface area example (animal)

surface area example (plant)

passive transport

1. diffusion of a substance across a membrane with no energy (ATP) investment

2. diffusion down concentration or electrochemical gradient (high to low concentration)

3. involved in the import and export of waste (diffusion, osmosis, facilitated diffusion)

4. includes hydrocarbons, CO2, O2, H20

diffusion

1. tendency for molecules to spread out evenly into the available space

2. moves randomly put diffusion of a population may exhibit a next movement in one direction

3. at dynamic equalibrium, as many molecules cross one way as cross in the other directions

4. Substances diffuse down their concentration gradient, the difference in concentration of a substance from one area to another

5. No work must be done to move substances down the concentration gradient

6. The diffusion of a substance across a biological membrane is passive transport because it requires no energy from the cell to make it happen

7. The following influence the rate of diffusion

- Concentration gradient

- Temperature

- Surface area

Osmosis

1. diffusion of water across a selectively permeable membrane

2. Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration

3. maintaining water balance is crucial for the survival of all organisms

Equilibrium

1. rate of diffusion decreases once equilibrium is reached

2. net rate of diffusion is zero

3. definition: state in which the concentrations on both sides of the semi-permeable membrane are the same (equal)

External environments can be hypotonic, isotonic, or hypertonic to internal environments of cell

Hypertonic Solution

1. Solute concentration is greater than that inside the cell; cell loses water

2. Hyper= high...the solute is high in a solution

3. when the solute is high the water is low, the cell will shrivel or crenate

Tonicity (don’t have to read all)

ability of an extracellular solution to cause a cell to gain or lose water

Depends on the concentration of solutes that cannot pass through the cell membrane

Cells can be in three types of solutions: isotonic, hypertonic, hypotonic

1. Cells immersed in an isotonic solution have no net movement of water

• The concentration of nonpenetrating solutes inside the cell is equal to that outside the cell.

• Water diffuses into the cell at the same rate water moves out of the cell

2. Cells immersed in a hypertonic solution lose water to their extracellular surroundings

• The concentration of nonpenetrating solutes is higher outside of the cell

• Water will move to the extracellular fluid, Cells shrivel and die

3. Cells immersed in a hypotonic solution gain water

• The concentration of nonpenetrating solutes is lower outside of the cell

• The cell will gain water

• Animal cells swell and lyse

• Plant cells work optimally

Isotonic solution

Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane; solute= solute

Hypotonic solution

1. Solute concentration is less than that inside the cell; cell gains water

2. Hypo= low...the solute is low in a solution

3. when the solute is low the water is high, the cell will swell and lyse

Hypertonic VS Isotonic VS Hypotonic Solutions

Facilitated diffusion

1. diffusion of molecules through the membrane via transport proteins

2. increases rate of diffusion for small ions, water, carbohydrates

3. 2 groups of transport proteins: channel and carrier

• each transport proteins is specific for substances it can facilitate movement for

Channel Proteins

1. provide a channel for molecules and ions to pass

2. hydrophlic

3. many are gated which means it only allows passage when there is a stimulus

4. aquaporins: specific channel protein for water

Carrier proteins

undergo conformational changes for substances to pass

Glucose transport Protein (carrier protein)

why isn’t energy required for facilitated diffusion

Energy is not required because the molecules are still moving down their concentration gradient

Osmoregulation

cells must be able to regulate their solute concentrations and maintain water balance

• Animal cells will react differently than cells with cell walls, like plants, fungi, and some protists

maybe important..

Turgid

firm, plant cells become this in hypotonic solutions as the swell until the wall opposes uptake

plant cell - isotonic

there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt

Plasmolysis

usually lethal effect, when a plant cell loses water (hypertonic environment), the membrane pulls away from the wall

difference between facilitated diffusion and diffusion

active transport

1. requires energy (atp)

2. performed by specific proteins embedded in the membranes

3. low-high concentrations

4. substances moving AGAINST the concentration gradient

5. examples: pumps, exo/endocytosis

Pumps

1. maintain membrane potential

• mp: voltage difference or unequal concentrations of ions across the membrane, resulting in an electrical charge; The cytoplasm is relatively negative in comparison to the extracellular fluid

• Voltage is created by differences in the distribution of positive and negative ions

• Two combined forces, collectively called the electrochemical gradient, drive the diffusion of ions across a membrane: A chemical force (the ion’s concentration gradient); An electrical force (the effect of the membrane potential on the ion’s movement)

2. ex, Electrogenic pumps: proteins that generate voltage across membranes, which can be used later as an energy source for cellular processes

• Sodium potassium pump: Animal cells will regulate their relative concentrations of Na+ and K+, 3 Na+ get pumped out of the cell, 2 K+ get pumped into cell, Results in a +1 net charge to the extracellular fluid

electrogenic pump

a transport protein that generates voltage across a membrane

sodium-potassium pump

1. the major electrogenic pump of animal cells

2. Animal cells will regulate their relative concentrations of Na+ and K+, 3 Na+ get pumped out of the cell, 2 K+ get pumped into cell, Results in a +1 net charge to the extracellular fluid

Proton pump

the main electrogenic pump of plants, fungi, and bacteria, pumps H+ out of cell

Bulk transport

1. occurs by exocytosis and endocytosis

2. Small molecules and water enter or leave the cell through the lipid bilayer or by transport proteins

3. Large molecules, such as polysaccharides and proteins,or other cells cross the membrane in bulk via vesicles

4. Bulk transport requires energy

exocytosis

1. transport vesicles migrate to the membrane, fuse with it, and release their contents

2. Many secretory cells use exocytosis to export their products (ex: nerve cells releasing neurotransmitters)

3. vesicles fuse with cell membrane, expel contents

endocytosis

1. the cell takes in macromolecules by forming vesicles from the plasma membrane

2. Endocytosis is a reversal of exocytosis, involving different proteins

3. There are three types of endocytosis:

• Phagocytosis (“cellular eating”)

• Pinocytosis (“cellular drinking”)

• Receptor-mediated endocytosis

4. take in macromolecules, form new vesicles

Phagocytosis

1. a cell engulfs a particle in a vacuole

2. The vacuole fuses with a lysosome to digest the particle

3. think “cellular eating” - solids

• Ex: white blood cell eating bacteria,Ameba eating another cell

pinocytosis

molecules are taken up when extracellular fluid is “gulped” into tiny vesicles, think “cellular drinking” - fluids

receptor-mediated endocytosis

binding of ligands to receptors triggers vesicle formation on cell surface

ligands

any molecule that binds specifically to a receptor site of another molecule