Biol 1111 Cell Structures and Functions

Cells

Smallest unit of life

Cell Theory

All living things are made of one or more cells, the cell is the basic unit of life, and all new cells come from existing cells (Schleiden, Schwann)

Prokaryotes

Bacteria and archaea, plasma membrane, cytoplasm, DNA, and ribosomes, no nucleus or no membrane-bound organelles, DNA is found in the nucleoid, flagella are used for movement

Eukaryotes

Animals, plants, fungi and protists, plasma membrane, cytoplasm, DNA, and ribosomes, DNA enclosed in a nucleus

Plasma Membrane

Made up of a phospholipid bilayer with embedded proteins that protects the cell from its environment

Cytoplasm

Made of organelles suspended in the gel-like cytosol + cytoskeleton

Cytoskeleton

Network of protein fibers that shapes the cell and anchors its organelles together

Microfilaments

Actin, thinnest fibers, supports microvilli and enables muscle contraction

Intermediate Filaments

Structural support, anchor organelle, teritin, strong enough to eventually split 50/50

Centrosome

The microtubule-organizing center in animal cells, contains a pair of centrioles

Flagella

Long, hair-like structures that extend from the plasma membrane and are used to move an entire cell

Cillia

Short, hair-like structure that moves a cell or moves material along a surface

The Endomembrane System

A group of membranes and organelles that modify, package, and transport lipids and proteins; includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles, “cell’s assembly line”

Nucleus

DNA chromatin directs ribosome and protein synthesis, enclosed by a double-membrane nuclear envelope, punctured with pores

Chromatin

DNA + proteins, condenses into visible chromosomes when a cell divides

ER

A network of membranous tubules continuous with the nuclear envelope, collectively modify proteins and synthesize lipids, abundant in cells that secrete a lot of protein, like liver cells

Rough ER

Studded with ribosomes, modifies proteins and makes membrane phospholipids,

ribosomes synthesize proteins while attached,

transferred here where they undergo modifications such as folding or addition of sugars

Smooth ER

Makes lipids and steroid hormones; detoxifies drugs and poisons, stores calcium

Golgi Apparatus

A stack of flattened membranous sacs that sorts, tags, and packages proteins and lipids;

receives transport vesicles from the ER on its receiving face,

adds sugar chains and molecular tags to route material to the right destination

Ships finished products in vesicles from its releasing face

Lysosomes

The cell’s “garbage disposal”, digests proteins, lipids, and worn-out organelles, enzymes work best at a low (acidic) pH, kept separate from the neutral cytoplasm, destroys pathogens engulfed by phagocytosis, as in macrophages, found in animal cells not really in plant cells

Vesicles

Membrane-bound sacs used for storage and transport, can fuse with other membranes in the cell

Vacuoles

membrane-bound sacs used for storage and transport, plants: larger, enzymes can break down macromolecules and regulates the cell’s water balance, loss from this can cause a plant to shrivel

Ribosomes

The cellular structures responsible for protein synthesis, made of a large subunit and a small subunit, free-floating in the cytoplasm, or attached to the Er or the nuclear envelope, especially abundant in cells that make a lot of protein (like immature red blood cells)

Mitochondria

Produces ATP through cellular respiration, double-membrane organelles with their own DNA and ribosomes, inner membrane folds (cristae) increase surface area for energy production, muscle cells are packed with these

Peroxisomes

Small, single-membrane organelles that carry out oxidation reactions, break down fatty acids and amino acids, detoxify poison (includes alcohol in liver cells), the byproduct, hydrogen is safely broken down into water and oxygen

Cell Wall

A rigid layer outside the plasma membrane, made of cellulose in plants

Chloroplasts

Carry out photosynthesis and have their own DNA and ribosomes

Thylakoids

Stack into grana, chlorophyll captures light energy

Endosymbiotic Theory

Mitochondria and chloroplasts were once free-living bacteria engulfed by an early host cell, both organelles have their own DNA and ribosomes (like bacteria)

Extracellular Matrix

Glycoproteins and collagen released by animal cells, holds tissue together, biochemical signaling, and tissue organization for surrounding cells

Plasmodesmata

channels correcting the cytoplasm of adjacent plant cells

Symplastic Pathway

Channels that let animal cells communicate directly

Plasma Membrane

Define’s the cell’s boundary and controls its contact with the environment, flexible enough to let cells like red and white blood cells change shape, carries markers that let cells recognize each other (“self” vs “non-self”)

Fluid Mosaic Model

Proposed by Singer and Nicolson (1972), describes the membrane as a “mosaic” (many components), of phospholipids, cholesterol, proteins, and carbohydrates, components can flow and shift position while the membrane stays intact

Phospholipid Bilayer

Transmembrane proteins span the membrane and act as channels or pumps, peripheral proteins attach to the surface, may act as enzymes or structural anchors, carbohydrates sit only on the exterior surface and help cells recognize each other

Hydrophilic

Heads face out, like water, polar

Hydrophobic

Tails face in, doesn’t like water, nonpolar

Selective Permeability

Plasma membranes are asymmetric (inside differs from outside), lipid-soluble substances (fat-soluble vitamins, O2, CO2) pass through easily, polar substances and ions need help (channels, carriers, or pumps), this is what keeps the cell’s internal environment stable

Diffusion

Passive movement of a substance from up to down the concentration (no energy required, naturally moves), continues until concentration is equal throughout the space (equilibrium), Rates increase with a bigger concentration gradient, higher temps, or smaller molecules, rates decrease as the density of the solvent increases

Facilitated Transport aka Facilitated Diffusion

Still passive, still follows the concentration gradient, moves substances that can’t easily cross the lipid bilayer on their own (ions and polar/ lipid bilayer of the cell membrane is hydrophobic), requires membrane transport proteins that act as channels or carriers, no ATP spent

Osmosis

Diffusion of free water molecules across a selectively permeable membrane, water moves toward the side with more solutes (less free water), only water moves, the membrane blocks the solute, subcategory of diffusion, continues until the water concentration gradient reaches zero

Tonicity

Compares the solute concentration of the extracellular fluid to the cytoplasm

Hypotonic

Fewer solutes (dissolves in liquid) outside → water enters the cell → cell may lyse (burst)

Hypertonic

More solutes outside → water leaves the cell → cell crenates (shrivels)

Isotonic

Equal solute concentration → no net water movement

Cyto

Normally slightly hypertonic, so water tends to enter, creates turgor pressure and keeps the pressure, cell walls in plants, fungi, and some protists prevent cell from lysing, in a hypertonic environment (such as a drought), water leaves and the plant shrivels

Electrochemical Gradients

Cell combines a concentration gradient and electrical gradient across membrane, cell interior is electrically negative relative to the extracellular fluid

EX: Na+: concentration and electrical gradients both favors moving into the cell

K+: the electrical gradient favors moving in, but the concentration gradient favors moving out

Primary Active Transport

Moves substances against their gradient- requires ATP, the sodium-potassium pump moves K+ into the cell and Na+ out of the cell, creates the concentration and charge difference across the membrane, sensitive to metabolic poisons that block ATP production

Secondary Active Transport

Uses the energy stored in an electrochemical gradient build by primary active transport, powers the movement of substances like amino acids and glucose into the cell, ATP synthesis itself relies on a hydrogen ion gradient in the mitochondrion, no direct ATP use at this step (ATP is used from primary), it “borrows” the gradient’s stored energy

Endocytosis

Moves large particles into the cell; the membrane pinches inward to form a vesicle

Phagocytosis

“Cell eating”, engulfs large particles

Pinocytosis

“Cell drinking”, takes extracellular fluid and solutes

Receptor-mediated endocytosis

Targets one specific substance using membrane receptors

Exocytosis

Expels material from the cell, a membrane-bound vesicle fuses with the plasma membrane, contents are released into the extracellular space, used to secrete hormones, enzymes, and other cell products