cell bio 3

fluid-mosaic model

membrane is a flexible phospholipid bilayer containing proteins and other molecules

lipid bilayer

two layers of lipids with water-attracting heads facing outward and water-repelling tails facing inward.

gorter and grendel experiment

• found that extracted membrane lipids covered about twice the cell's surface area, supporting the bilayer model

• scientists extracted lipids from red blood cells (RBCs), spread them into a monolayer on a Langmuir trough, and measured the area

• the lipid monolayer had twice the surface area of the cells, supporting the idea that membranes contain a lipid bilayer

Amphipathic

Has both hydrophilic and hydrophobic regions

Hydrophilic

Attracted to water; usually polar or charged

Hydrophobic

Repelled by water; usually nonpolar.

Phosphoglycerides

membrane lipids with glycerol, two fatty acid tails, and a phosphate-containing head group

Phospholipid head groups

choline and ethanolamine are neutral; serine is negative; inositol is neutral and can be phosphorylated to form PIP₂

Sphingolipids

Lipids with a sphingosine backbone and a fatty acid

Sphingomyelin

A sphingolipid especially common in neurons

Glycolipids

lipids with attached sugars, mainly in the outer membrane layer; can be part of lipid rafts

Cholesterol

an amphipathic lipid with a hydroxyl head and a steroid-based region; helps regulate membrane fluidity and stability

Liposomes

artificial lipid vesicles made by dissolving lipids in organic solvent, evaporating the solvent, adding buffer, and agitating

Membrane fluidity

affected by temperature, fatty acid chain length, saturation, head groups, and cholesterol

lateral diffusion

lipids move sideways rapidly within the same membrane layer; flip-flop between layers is much slower

FRAP

fluorescence recovery after photobleaching; measures how quickly fluorescent membrane molecules move into a bleached area

lipid asymmetry

inner and outer membrane layers have different lipid compositions

lipid rafts

specialized membrane regions enriched in certain lipids, including cholesterol and some glycolipids

cholesterol experiment

removing cholesterol or inhibiting its synthesis makes membranes more likely to break under shear or hypotonic stress

peripheral proteins

attach to the inner or outer membrane surface; can be removed using salt, pH changes, or chelating agents

integral proteins

embedded in the bilayer; usually require detergent for extraction

non-ionic detergent

• Breaks apart the fatty membrane so the proteins can be removed.

• helps extract integral membrane proteins while better preserving their function

transmembrane domain

the part of a protein that passes through the cell membrane

alpha helix

the most common membrane-spanning structure; its hydrophobic amino acids interact with the membrane's fatty acid tails

glycophorin

a single-spanning membrane protein with 23 hydrophobic amino acids in its transmembrane helix; forms a homodimer

beta barrel

a membrane-spanning structure made from folded beta sheets; some form pores

glycosylation

addition of sugars to proteins, often on extracellular or organelle-lumen-facing regions

disulfide bonds (S–S)

bonds that help stabilize protein structure

freeze-fracture TEM

freezes and splits membranes to reveal membrane organization and integral proteins

heavy-metal shadowing

coats specimens with metals such as platinum and/or carbon for electron microscopy; rotating the specimen can improve resolution

lectins — Proteins that bind specific sugars

-patching and capping — Antibody- or lectin-bound membrane proteins cluster together

FRAP and FLIP

fluorescence techniques used to study membrane protein mobility

cytoskeleton attachment

can limit movement of proteins inside cell membrane

• also provides structure, shape and support for the cell

passive diffusion

small nonpolar molecules, such as O₂ and CO₂, move down their concentration gradient without energy; movement depends on the gradient and hydrophobicity

protein-assisted transport

transport proteins help ions, sugars, amino acids, and some water cross membranes

active transport

uses energy, often from ATP, to move substances against their concentration gradient

ATP-powered pumps

use ATP hydrolysis to move substances; examples include sodium-potassium pumps and hydrogen-ion pumps

osmosis

passive movement of water down its concentration gradient

channel proteins

form tunnels for specific ions or water; some are gated. They can transport molecules very quickly, around 100 million per second in the lecture notes

carriers/transporters

bind one or a few molecules and change shape to move them across; approximately 100–10,000 molecules per second in the notes

facilitated diffusion

carrier-mediated movement down a concentration gradient without direct energy input

uniporter

moves one type of molecule in one direction down its gradient

symporter

moves two substances in the same direction

antiporter

moves substances in opposite directions

cotransporter

uses one substance moving down its gradient to drive another substance against its gradient

glucose absorption in the gut

a sodium-glucose symporter brings glucose into intestinal cells; the sodium-potassium pump moves sodium out and potassium in to keep sodium low inside the cell, and the glucose uniporter lets glucose leave the cell and enter the blood.

Robert K. Crane

proposed sodium-glucose cotransport

ernest m. wright

reconstituted the transport mechanism into liposomes

How do you extract peripheral proteins?

use salt, pH changes, or chelating agents

How do you extract integral proteins?

use a suitable detergent, preferably mild and non-ionic to preserve function

how can you study purified membrane proteins?

reconstitute them into liposomes

blobin experiment: how can you identify a peripheral protein?

treat ghost membranes with salt, pH changes, or EDTA; if blobin is released into the supernatant, it is peripheral.

blobin experiment: How can you identify an integral protein?

it stays with the membrane pellet after peripheral protein extraction and is released after detergent treatment.

blobin experiment: How can you determine which side blobin faces?

compare treatment of intact cells with treatment of open ghost membranes; release only from ghosts supports a cytoplasmic location

which detergent should be used to test blobin's interaction with an integral membrane protein?

a non-ionic detergent, to better preserve protein function.

metabolism

all chemical reactions that break down food, release energy, and build needed molecules

metabolic enzymes

catalyze reactions that break down nutrients or make amino acids, lipids, carbohydrates, and nucleotides

storage molecules

extra energy is stored mainly as triglycerides and glycogen; these can be broken down when needed

vitamins

small molecules obtained from food that help enzymes work

metabolic disease examples

diabetes affects glucose metabolism; phenylketonuria (PKU) prevents normal breakdown of phenylalanine and can damage the brain without dietary management

glycolysis

occurs in the cytoplasm and breaks one 6-carbon glucose into two 3-carbon pyruvates

what is glycolysis's net output?

2 ATP and 2 NADH per glucose. It uses 2 ATP and produces 4 ATP

aerobic pathway

uses oxygen and mitochondria to produce much more ATP

anaerobic pathway

occurs without oxygen and produces much less ATP

aerobic cellular respiration equation

overall equation — C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

four stages of aerobic respiration

glycolysis → pyruvate oxidation → citric acid cycle → electron transport chain and oxidative phosphorylation

pyruvate oxidation

each pyruvate becomes acetyl-CoA, releasing CO₂ and producing NADH

citric acid cycle

breaks down acetyl-CoA, releasing CO₂ and producing NADH, FADH₂, and GTP/ATP

mitochondria

organelles with two membranes; the endosymbiotic hypothesis proposes they evolved from bacteria

MPC (mitochondrial pyruvate carrier)

transports pyruvate into mitochondria; its proteins were identified in 2012. MPC1 mutations can cause disease

why are mitochondria important?

training can increase mitochondrial capacity; mitochondria support cancer-cell energy and building needs; mitochondrial quality control is linked to aging and neurodegeneration

products per glucose in the lecture notes

10 NADH, 2 FADH₂, 4 ATP/GTP by substrate-level phosphorylation, and 6 CO₂

substrate-level phosphorylation

direct production of ATP or GTP during a metabolic reaction

electron transport chain

• 4 protein complexes that pass electrons along and use their energy to pump H⁺ (protons) into the space between the mitochondrial membranes

four large protein complexes in the inner mitochondrial membrane transfer electrons and help pump H⁺ into the intermembrane space

Complex I

Accepts electrons from NADH and pumps H⁺.

Complex II

Accepts electrons from FADH₂-linked reactions and passes them to CoQ; does not pump H⁺.

CoQ (ubiquinone)

fat-soluble mobile carrier that transfers electrons through the membrane

complex III

transfers electrons from Q to cytochrome c onward and pumps H⁺

cytochrome c

small, water-soluble mobile electron carrier

Complex IV

transfers electrons to oxygen, the final electron acceptor, forming water; pumps H⁺

other ETC components in cellular respiration

flavoproteins contain FAD/FMN; cytochromes contain iron in heme; iron-sulfur proteins contain iron and sulfur; some proteins contain copper

proton gradient

H⁺ becomes more concentrated in the intermembrane space than in the matrix

chemiosmosis

H⁺ flows back down its gradient through ATP synthase, providing energy to make ATP from ADP + Pi

ATP synthase

enzyme that makes ATP using energy from the proton gradient

oxidative phosphorylation

ATP production powered by electron transport and the proton gradient

how was the proton-gradient idea tested?

vesicles containing ATP synthase and bacteriorhodopsin made ATP when light caused H⁺ to be pumped across the membrane

ATP yield in the lecture notes

approximately 32–34 ATP from oxidative phosphorylation and 36–38 ATP total per glucose

fermentation

regenerates NAD⁺ so glycolysis can continue when oxygen is not available; yields only 2 ATP per glucose.

lactic acid fermentation

produces lactate; used in making yogurt, sauerkraut, and some cheeses.

alcohol fermentation

produces ethanol and CO₂; used in beer, wine, and bread production

anaerobic respiration

some bacteria use nitrate, carbonate, or sulfate instead of oxygen as the final electron acceptor; it produces more ATP than fermentation but less than aerobic respiration

how do fats enter respiration?

glycerol can enter glycolysis; fatty acids are converted to acetyl-CoA.

how do proteins enter respiration?

amino acids are broken down into metabolic intermediates, such as pyruvate

photosynthesis overall equation

6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂

purpose of photosynthesis

uses light energy to make reduced carbon compounds and releases oxygen into the atmosphere

chloroplast

organelle where photosynthesis occurs

thylakoid

membrane system where light reactions occur

stroma

fluid-filled region where the Calvin cycle occurs

Two stages of photosynthesis

• light-dependent reactions: produce ATP and NADPH in thylakoid membrane in chloroplast, uses light and water

• Calvin cycle: stroma of chloroplast, uses them to help make sugars from CO₂

chlorophyll

absorbs light for photosynthesis and becomes excited, allowing electrons to be transferred

• In the thylakoid membranes of chloroplasts.