Ap Bio Unit 2 Khan Academy

Intro to Eukaryotic Cells

• Lysosomes must maintain an acidic pH in order to dispose of cellular waste

Peroxisomes carry out chemical reactions called oxidation reactions and produce hydrogen peroxide - both would damage the cell if they werent “stored away”

• ability to maintain different environments inside a single cell; allows eukaryotic cells to carry out complex metabolic reactions

Eukaryotic Cells Have: ( that prokaryotic cells don’t)

1. membrane-bound nucleus that houses genetic material

2. # of membrane-bound organelles

3. multiple linear chromosomes as opposed to the single circular chromosomes of prokaryotes

The Endomembrane System

• endomembrane system - group of membranes and organells in eukaryotic cells that work togther to modify, package, and transport lipids and proteins

  • includes: enoplasmic reticulum (ER), golgi apparatus, nuclear envelope, lysosomes, and plasma membrane

  • does not include: mitochondria, chloroplasts, or peroxisomes

• endoplasmic reticulum - plays an important role in the modification of proteins and the synthesis of lipids

  • consists of a network of membranous tubules and flattened

  • space inside sacs and tubules is called lumen

• rough ER - has ribosomes that make proteins and feed the newly forming protein chains into the lumen

  • modified proteins are packaged into vesicles and be shipped to the golgi apparatus

  • rough ER also makes phospholipids

• the smooth ER can:

  • synthesize carbs, lipids, and steroid hormones

  • detoxify medications and poisons

  • store calcium ions

• transitional ER - “smooth” patches on rough ER - exit sites for vesicles budding off from the rough ER

• golgi apparatus - storing, tagging, packaging, and distributing of lipids and proteins

  • receiving side is called the cis face

  • opposite side is called the trans face

  • in the golgi apparatus, short chains of sugar molecules might be added or removed, phosphate groups attached as tags

• lysosomes - organelle that contains digestive enzymes and acts as organelle - recycling facility

  • can digest foreign particles that are brought into the cell

  • large central vacuole (in plant cells) stores water and waste, isolates hazardous materials, and has enzymes that can break down macromolecules and cellular components

• peroxisomes - houses enzymes involved in oxidation reactions, which produce hydrogen peroxide as a by-product

  • does not receive vesicles from the golgi apparatus

Mitochondria & Chloroplasts

• mitochondria - breaks down fuel molecules and captures energy in cellular respiration

• photosynthesis is used to build sugars

  • energy contained in the sugars is harvested through cellular respiration

• in chloroplasts, thylakoids are in stacks called grana (singular = granum)

• intermembrane space - space between membranes

• mitochondrial matrix - compartment enclosed by the inner membrane

• endosymbiosis - scientific type of symbiosis where one organism lives inside the other

Structure of the Plasma Membrane

• cell membrane:

  • defines borders of cell

  • allows cell to interact with its environment in a controlled way

• lipids create a semi-permeable barrier between the cell and its environment

• proteins are involved in cross-membrane transport and cell communication

• carbohydrates helps cells recognize each other (decorate proteins and lipids)

plasma membrane - mosaic of components (phospholipids, cholesterol, and proteins) that move freely and fluidly in the plane of the membrane

glycoprotein - protein with carb attached

glycolipid - lipid with carb attached

phospholipid - lipid made of glycerol - 2 fatty acid tails, and a phosphate - linked head group

phospholipid bilayer - 2 layers of phospholipids with their tails pointing inwards

• cholesterol is found in the core of the membrane

• carbohydrate groups are present only on the outer surface of the plasma membrane and are attached to proteins

• phospholipids are well-suited for the fabric of the plasma membrane because they are amphipathic

amphipathic - have both hydrophobic and hydrophilic regions

• hydrophilic: its head- contains a (-) charge

  • forms charge-based interactions with the phospholipid heads

• hydrophobic: contains nonpolar fatty acid tails

  • interact poorly w/ water so tails are tucked in the interior of the membrane

phospholipid ampthipathic structure makes a good barrier because water and other charged substances cannot easily cross the hydrophobic core

phospholipids have small tails - micelle - small, single-layered sphere

have bulkier tails - liposome - hollow droplet of bilayer membrane

Integral Membrane Proteins

• at least one hydrophobic regoin that anchors them to the core of the phospholipid bilayer

• transmembrane proteins - extend all the way across the membrane

• those exposed to the cytoplasm are hydrophilic

Peripheral Membrane Proteins

• found on the outside or inside surface of membranes

• attached either to integral proteins or phospholipids

• do not stick into the hydrophobic core of the membrane

Carbohydrates

• found on the outside surface of the cells

• are bound to proteins or lipids

• form distinctive cellular markers: allows cells to recoginze each other

  • this allows immune system to differentate between body cells (shouldnt attack) and foreign cells or tissues (should attack)

-at cooler temps. - straight tails or saturated fatty acids can pack tightly togther and make a dense and failry rigid membrane

-phospholipids with unsaturated fatty acids cannot pack tightly (because of bends) and membrane will stay fluid at lower temps.

-cholesterol - helps to minimize the effects of temp. on fluidity

• low temps. - increases fluidity

• high temps - reduces fluidity

cholesterol expands the range of temps. at which membrane maintains a functional and healthy fluidity

Component Location

• phospholipids - main fabric of membrane

• cholesterol - tucked between hydrophobic tails of the membrane phospholipids

• integral proteins - embedded in the phospholipid bilayer; may or may not extend through both layers

• peripheral proteins - on the inner or outer surface of the phospholipid bilayer, but not embedded in its hydrophobic core

• carbohydrates - attached to proteins or lipids on the extracellular side of the membrane (forming glycoproteins and glycolipids)

Prokaryote and Eukaryote Differences

Prokaryotes

• Dna is circular - free-floating in cytoplasm

• No nucleus - no membrane-bound organelles

• Small (1-5 micrometers)

• Bacteria - archea

• always unicellular

Eukaryotes

• Dna is linear - found in the nucleus

• has nucleus and membrane-bound organelles (i.e mitochondria, golgi body, ER, chloroplasts)

• Larger (10-100 micrometers)

• animals, plants, fungi, protists

• can be unicellular or multicellular

  • more protists are unicellur

The Extracellular Matriz and Cell Wall

-most animal cells release materials into the extracellular space creating a complex meshwork of proteins and carbohydrates caled the extracellular matrix

• major component of the ECM is the protein collagen - assemble into long fibers called collagen fibers

-collagen gives tissues strength and structural intergrity in ECM..

• collagen fibers are interwoven with a class of carb-bearing proteoglycans

  • may be attracted to a long polysacchride backbone

-ECM is connected to cells it surrounds

• key connectors are proteins called intergrins

  • embedded in the plasma membrane

-fibronectin act as bridges between integrins and collagen

-integrins anchor the cell to the ECM and helps tense its environments

-ex: blood clotting - when cells lining a blood vessel are damaged, they display a protein receptor called tissues factor: this is presented to the ECM and triggers a range of responses

-cell wall - rigid covering that surrounds the cell, protecting it, and giving it support and shape

• major organic molecules is cellulose - polysaccharide composed of glucose units

  • cellulose assembles into fibers called microfibrils

other polysaccharides found: nemicellulose and pactin

-middle lamella - sticky layer that helps hold the cell walls of adjacent plant cells together

Passive Transport Review

-passive transport - transport that does not require energy (ATP)

-concentration gradient - region of space over which the concentration of a substance changes

-permeability - quality of a membrane that allows substances to pass through it

-equilibrium - state at which a substance is equally distributed throughout a space

-in diffusion, substances move from high to low concentration until the concentration becomes equal throught the space

-only small, uncharged substances like CO2 and O can easily diffuse across the cell membrane

• charged ions or large molecules require different kinds of transport

-gases can easily diffuse easily between the phospholipids of the cell membrane

• many polar or charged substances (like chloride) need help from membrane proteins/channel proteins

-substances transported through facilitated diffusion still move with the concentration gradient, but transport proteins protect them from hydrophobic region

Active Transport

-active transport - transport that requires an input of energy to occur

-ATP - adenine triphosphate - primary energy carrier in living things

-during active transport, substances move against the concentration gradient from low to high concentration

-requires assistance from carrier proteins, which change conformation when ATP hydrolysis occurs

-channel proteins are not used in active transport

Bulk Transport

-bulk transport mechanisms involve enclosing substances in membrane which can bud from or fuse with the membrane

-energy requiring and energy-intensive process

-endocytosis - general term for the various types of active transport that move particles into a cell by enclosing them in a vasicle made of plasma membrane

-phagocytosis - form of endocytosis in which large particles (such as cells or cell debris) are transported into the cell

• used by a macrophage to engulf a pathogen

-pinocytosis - form of endocytosis in which a cell takes in small amounts of extracellularfluid

-receptor - mediated endocytosis - form of endocytosis in which receptor proteins on the cell surface are used to capture a target molecule

• transmembrane protein receptors cluster in regions of the plasma membrane known as coated pits (ex: clathrin)

-exocytosis - form of bulk transport in which materials are transported from the inside to the outside of the cell in membrane-bound vesicles that fuse with the plasma membrane

Cell Size

-the limitation for how small a cell can get its storage of complex material and organelles to carry out their functions

-each unit of surface area has to process inputs and outputs of the cell

-volume increases faster than surface area

-at some point, the surface area cannot handle the amount of inputs and outputs that are needed to maintain the cell

-as the cell gets larger - things also have to be transported across larger distances

-cells maximize their surface area by stretching out or having areas that stick out

Facilitaed Diffusion

-aquaporins - channel proetin specialized for the transport of water

-facilitated diffusion can happen through channel proteins or carrier proteins (changes shape to facilitate diffusion)

• passive transport

  • allows charged or polar molecules to pass through hydrophobic regions

-channel proteins transport material more quickly than carrier proteins

-electrochemical gradient - combination of the electro gradient and the concentration gradient

-electro gradient - there is more positive potential (positive charged ions) on the outside of the cell, so ions want to go to the inside - source of potential energy

-symporter used potential energy frm ions to transport glucose against its concentration gradient - secondary active transport

-anitporter - a substance moving with its concentration gradient is providing the energy for another substance to move against its concentration gradient

• substances move in opposite directions

• secondary active transport

-secondary active transport - uses an elctrochemical gradeint - generated by active transport - as an energy source to move molecules against their gradient

-sodium - potassium pump - moves Na+ out of the cell and K+ into them

• uses ATP as energy source

• important in animal cells

• maintains correct concentrations of Na+ and K+ in cells and generates the voltage across the cell membrane in animal cells

• process involves the protein going between 2 forms: in-ward facing with high affinity for sodium and out-ward facing with a high affinity for potassium

Osmosis and Tonicity

-osmosis - net movement of water across a semipermeable membrane frm an area of lower solute to an area of high solute concentration

• the more solute water contains, the less apt it will be to move across a membrane into an adjacent compartment - result is net flow of water frm low solute to high solute concentration

-osmolarity - total concentration of solutes in a solution (low osmolarity has less solute particles per liter of solutions)

-hyperosmotic - higher osmolarity

-hypoosmotic - lower osmolarity

-isoosmotic - same osmolarity