Cell & Molecular Bio Unit 3

Oxidaition

Molecule looses electrons during a reaction

Reduction

Molecules gain electrons during a reaction

Plasma Membrane

Boundary that separates living cells from its surroundings to create a unique environment within cells

Roles of membranes

• concentrating solutes

• selective barrier

• scaffolding for chemical reactions

• responding to external stim

• maintain electric potential

Unsaturated Fatty Acids

Contains double bonds which allow for fluidity because it creates a less compact membrane stucture - allows for fluidity to be maintained in cold environents because colder temps are required to solidify

Saturated Fatty Acids

Tails do not contain double bonds which allows them to be packed together to form less permeable structures that solidify at room temp

Membrane Leaflets

Inner and outter monolayers that make up the phospholipid bilayer of the membrane

Increasing Fatty Acid Length

Increases membrane viscosity

Glycolipids

Have hydrocarbon tails that contain saccarides which are needed for cell recognition and anchoring cells

Effects of Cholesterol in Warm Temps

Restrains the movement of phospholipids by taking up space and preventing easy movement of fatty acid tails

Effects of Cholesterol in Cold Temps

Maintains membrane fluidity by preventing fatty acid tails from packing tightly together

Micelles

Spherical or ellipisodial structures that are amphipathic and form spontaneously

Liposomes

Grown bilayer that encloses into a spherical structure with hydrophoic tails completely enclosed and an aqueous interior environment

Vesicles

Bilayers that also contain proteins and other molecules which are enclosed into a spherical structure with an aqueous interior environment

Where does lipid synthesis take place?

Smooth ER

Where does membrane bound protein synthesis take place?

Rough ER

Endosymbiotic Theory

Eukaryotic cells evolved when large anaerobic prokaryotic cells engulfed smaller aerobic bacteria such as mitochondria and chloroplasts which created a permenant symbiotic relationship built on ATP exchange.

Lipoproteins

Complexes that allow human cells to absorb fatty acids so they don’t need to be synthesized

Chylomicrons

Type of lipoprotein that transports dietary lipids to adipose tissue

Very Low Density Lipoproteins (VLDL)

Transports triglycerides form hepatocytes to adipocytes

Low Density Lipoproteins (LDLs)

Carries about 75% of total cholesterol in blood to deliver to liver to cells

High Density Lipoproteins (HDLs)

Remove excess cholesterol from body cells & blood and transports it to liver for elimination

Why is fermentation less efficient than aerobic respiration?

Fermentation stops at the end of glycolysis, making glycolysis the sole producer of ATP

• oxygen is much more electronegative than the alternatives

What are lipid bilayers impermeable to?

ions, charged molecules, large polar molecules (water soluble)

Effect of change in membrane potential

Changes in membrane potential alters the probability that the channel will be found in its open conformation

Reverse Beta Oxidation

Metabolic pathway involving acetyl coA is reversed after sugars are broken down and bonds are rebuilt to allow for storage in the form of fatty acids

Useful energy is obtained by cells when sugars derived from food are broken down by which processes?

Glycolysis, krebs cycle, oxidative phosphorylation

Glycocalyx

The formation of the gel like layer composed of glycolipids, glycoproteins, and sugars that surrounds the outside of the cell

Peripheral Proteins

Bound to the membrane surface

Integral Proteins

Penetrate the hydrophobic core of the membrane & have hydrophobic stratches of nonpolar amino acid residues

Transmembrane Proteins

Integral proteins that span the cell membrane

6 Major Functions of Membrane Proteins

• Transport

• Enzymatic activity

• Signal transduction

• Cell - cell recognition

• Intercellular joining

• Attatchment to cytoskeleton and extracellular matrix

Exocytosis

Active transport where cells move molecules from cytoplasm to extracellular fluid using vesicels - typically neurotransmittters/hormones/waste

Endocytosis

Active transport where cells ingest macromolecules by forming vesicles and transporting them across the plasma membrane

Types of Endocytosis

• Phagocytosis: Cell eating

• Pinocytosis: Cell drinking

• Receptor Mediated Endocytosis

Active Transport

• Energy dependent

• Goes against concentration gradient: low to high concentration

• Uses protein pumps and vesicles

• Used to maintain homeostasis

Passive Transport

• ATP independent

• Follows the concentration gradient: high to low concentration

• Driven by concentrations for cellular equilibrium

• Uses protein pumps, vesicles, diffusion

Types of Passive Transport

• Simple diffusion

• Facilitated diffusion

• Osmosis

• Filtration

Simple Diffusion

Movement of small nonpolar molecules such as O₂ & CO₂ directly through the lipid bilayer

Facilitated Diffusion

Movement of large polar molecules such as glucose and ions through the plasma membrane using carrier or channel proteins

Osmosis

Diffusion of water through selectivly permeable membranes from low solute concentration to high solute concentration using aquaporins [membrane channel] to cross membrane

Carrier Proteins

Transporters: facilitate diffusion by binding to molecule with induces conformational changes, allowing the solute to pass through the carrier protein across the plasma membrane

Tonicity

The ability of a surrounding solute to cause cells to gain or loose water - caused by osmotic pressue

Hypertonic Solute

Solute concentration is higher outside of cell which causes water loss = plasmolized (plant cell is shreiveled)

Hypotonic Solute

Solute concentration inside the cell is higher than outside which causes water gain = turgid (normal for plant cells)

Isotonic Solute

Solute concentration is equal inside and outside of the cell = flaccid for plant cells

Electrochemical Gradient

Protein pumps that push charged ions against their concentration gradient create a charge difference between the cell & ECM that acts a battery for the cell with stored energy that can be used for ATP synthesis and other chemical processes

Examples of Electronegative Protein Pumps

• Sodium/Potassium pump: expels 3 Na⁺ ions and takes in 2 K⁺ ions → used in animal cells

• Proton pump: expels H⁺ ions into ECM using ATP hydrolysis → used in plants/bacteria/fungi cells

Where does the oxidative stage of food breakdown take place?

Mitochondria

Glueconeogenisis

The synthesis of glucose from small oragnic molecules like pyruvate

How do plants and animals store fat?

Triacylglycerol

In eukaryotic cells, what is the final electron acceptor in the electron transport chain?

O₂

Most of the energy for the synthesis of ATP comes from which molecule?

NADH produced during krebs cycle

Which activated carriers are produced by the krebs cycle?

GTP, NADH, FADH₂

Ion Channels

• Passive transporter

• Permeable in both directions

• Electrochemical gradient determines direction of ion flow

Voltage Gated Ion Channel

Channel only opens when membrane potential is within a certain range such as propagating signals down axons of neurons

Ligand Gated Ion Channel

Channel only opens when a molecule such as signal molecule/neurotransmitter/hormone binds to channel

Mechanially Gated Ion Channel

Channel responds to stress on the cell and/or changes in the membrane fluidity → Responds to sound and touch

Resting Membrane Potential

Sodium-potassium pumps generate membrane potential but potassium leak channels prevent the overshoot of pumping

Endomembrane System

Network of membranes and organelles in eukaryotic cells that work together to synthesize, modify, package & transport proteins and lipids

Major Areas of the Endomembrane System

• Protein targeting

• Vesicular transport

• Secretory pathways

• Endocytic pathways

Organelles in Endomembrane System

• Nucleus

• ER

• Golgi body

• Lysosomes

• Endosomes

• Peroxisomes

Endosomes

Membrane bound vesicles that act as a sorting and transpot hub for materials

Golgi Body

Modification, sorting, packaging of proteins & lipids for either secretion or delivery to another organelle

Evolution of ER

Archaeal ancestory developed in-folds in the plasma membrane for all eukaryotes to increase surface area allowing for more efficent exchanges for nutrients and waste

Where is protein synthesis concentrated?

In-folded membrane

Where is the topological distribution of ribosomes?

Cytosol

Primitive Nucleus

In-folds broke off of the plasma membrane with the cell’s chromosome to evolve into the ER and form the nucleus

Evolution of Nuclear Envelope

The inner portion of the ER became specialized in housing the cell’s chromosome and evolved into the nuclear envelope

Nuclear Pores

A property of the nuclear envelope to regulate the movement of molecules into and out of the nucleus through pores

Evolution of Mitochondria

Incorporation of aerobic bacterium through an endosymbyotic relationship between alphaproteobacteria and the host cell allowed for increased efficency of ATP production in exchange for protection from the environment

ER Signal Sequence

A hydrophobic domain that is either synthesized as the first sequence at the N terminus or as an internal sequence

Signal Recognition Particle

Binds to the ER signal sequence and allows for translocation to the ER where is binds to the SRP receptor on the rough ER

Protein Translocator

A transporter that allows the hands off the growing polypeptide to be fed into the lumen of the ER

Signal Peptidase

After the loopcreated by the ER signal protein grows, the polypeptide folds and the sequence is cleaved off and the folded protein is released as a soluble protein into the ER lumen

Single Pass Transmembrane Proteins

Polypeptide contains ER signal sequence and a hydrophobic sequence that acts as a stop transfer sequence which discharges the polypeptide chain and allows it to move through the membrane

Double Pass Transmembrane Proteins

The ER signal sequence isn’t located at the N terminus, it acts as a start transfer signal and helps to anchor the final protein in the membrane. The signal sequence doesn’t get cleaved off

Multipass Transmembrane Proteins

Have additional hydrophobic stop transfer sequences