Unit 2- Cell Structure and Function

nucleus

Contains the cell's DNA and mRNA, surrounded by double membrane (nuclear envelope) and controls its growth and reproduction, contains chromatin, continuous with rough er

mitochondria

• Sites of aerobic respiration

• Major energy production centers in cells

• Produce ATP

• Double membrane: outer and inner

• Membranes important for:

  • Intracellular digestion

  • Recycling of cell’s organic materials

  • Programmed cell death

ribosomes

are floating in cytoplasm or attached to the ER, synthesizes proteins based on mRNA sequence, composed of rRNA, has a small and large subunit, found in all forms of life

rough ER

has ribosomes attached and plays a role in protein synthesis, protein, and protein folding, packages proteins for secretion send transport vesicles to golgi, make replacement membrane

smooth ER

A network of membranes for transporting and synthesizing lipids, metabolize carbs, detox drugs & poisons, store Ca²⁺

golgi apparatus

Modifies, sorts, and packages proteins and lipids for transport within or out of the cell, produce lysosomes. Stack of membranes flattened sacs and is directly associated with the ER

lysosomes

Contain hydrolytic enzymes that are necessary for intercellular digestion of macromolecules. Degrade worn out organelles. Products of their degradation can be reused

vacuoles

Membrane-bound sacs that store water, nutrients, and waste. Plant cells have a large central, membrane-bound vesicles

cytoskeleton

Play numerous roles in the cells such as support, structure, and movement

cell membrane

Thin membrane is essential in controlling exchange between the cells and its environment. Acts as a barrier, but allows a controlled traffic if materials across it in both directions. Partially semi-permeable

vesicle

contains newly synthesized proteins separate from the end of the rough ER. Used to ship them to other parts of the cell or outside the cell, can also be shipped to the Golgi Apparatus

nucleolus

used in the production of ribosomes

chromatin

uncondensed DNA and serves as the blueprint for controlling the cells functions and for building more cells, complex of DNA and proteins; makes up chromosomes

cytoplasm

aqueous material contains numerous other organelles

peroxisomes

responsible for protecting the cells as they rid the body of toxic, detox alcohol, break down fatty acids, involves the production of hydrogen peroxide

cilia

short and numerous; locomotion or move fluids, Have “9+2 pattern” of microtubules

flagella

long and few; propel through water

microtubules

maintenance of cell shape; cell mobility; chromosome movements in cell division; organelle movements

microfilaments

also known as actin filaments, maintenance of cell shape; changes in cells shape; muscle contraction cytoplasmic streaming (plant cells); cell movement, cell division (animal cells)

intermediate filaments

maintenance of cell shape; anchorage of nucleus and certain other organelles; formation of nuclear lamina

prokaryotes

no nucleus, DNA in nucleoid,, no organelles other than ribosomes, small, evolutionary

prokaryote examples

domain bacteria and archaea

eukaryotes

nucleus and nuclear envelope, membrane bound organelles with specialized structure and function, larger in size, more complex

examples of eukaryotes

protists, fungi, plants, and animals

common of both eukaryotes and prokaryotes

Have DNA, cytoplasm, ribosomes, plasma membrane for cellular transport

Large surface area

Allows higher rates of chemical exchange between cell and environment

small intestine

highly folded surface to increase absorption of nutrients

root hairs

extensions of root epidermal cells; increase surface area for absorbing water and minerals

nuclear pores

control what enters/leaves nucleus

nucleolus

region where ribosomal subunits (rRNA and proteins) are formed

free ribosomes

float in cytosol, produce proteins used within cell

bound ribosomes

attached to ER, make proteins for export from cell

cis golgi

receives vesicles

trans face

ships vesicles

central vacuole

in plants, stores water, ions; retains water for turgor pressure

cristae

folds of inner membrane; contains enzymes for ATP production; increased surface area to increase ATP made

matrix

fluid-filled inner compartment, krebs cycle occurs here

chloroplasts

site of photosynthesis, double membrane, thylakoid disks in stacks (grana); stroma (fluid), contains chlorophylls (pigments) for capturing sunlight energy

centrosomes

region from which microtubules grow, also called microtubule organizing center, animal cells contain centrioles

cell wall

protect plant, maintain shape, composed of cellulose or chitin

plasmodesmata

channels between cells to allow passage of molecules from cell to cell

extracellular matrix

Outside plasma membrane of animal cells, composed of glycoproteins (ex. collagen), strengthens tissues and transmits external signals to cell

plant cells

central vacuoles, chloroplasts, cell wall of cellulose, plasmodesmata

animal cells

Lysosomes, centrioles, flagella, cilia, desmosomes, tight, and gap junctions, extracellular matrix (ECM)

endosymbiotic theory evidence

Double-membrane structure, have own ribosomes & DNA, reproduce independently within cell

endosymbiotic theory

The concept of going from prokaryotes to eukaryotes, a large prokaryote engulfs the small prokaryote which explains why mitochondria and chloroplasts and other organelles. Mitochondria and chloroplast have similar origin Explains membrane because it gets a double membrane, both have their own ribosomes and DNA, reproduce independently with cell (prokaryote asexual, eukaryote mitochondria and chloroplast)

selectively permeable

Allows some substances to cross more easily than others, example is plasma membrane

fluid mosaic model

Fluid: membrane held together by weak interactions, Mosaic: phospholipids, proteins, carbs

phospholipids

Bilayer, Amphipathic = hydrophilic head, hydrophobic tail, Hydrophobic barrier: keeps hydrophilic molecules out so it can pass through the transmembrane structure

low temperatures

phospholipids w/unsaturated tails (kinks prevent close packing) causing membrane fluidity allowing cells to continue their function

cholesterol resists changes by

limit fluidity at high temps, hinder close packing at low temps

example of membrane fluidity

bacteria in hot springs (unusual lipids); winter wheat (🡩 unsaturated phospholipids)

integral proteins

Embedded in membrane, Transmembrane with hydrophilic heads/tails and hydrophobic middles

peripheral proteins

Extracellular or cytoplasmic sides of membrane, NOT embedded, Held in place by the cytoskeleton or ECM, Provides stronger framework

Some functions of membrane proteins

Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, attachment to the cytoskeleton and extracellular matrix (ECM)

carbohydrates

• Function: Cell-cell recognition, important in developing organisms.

• Types: Glycolipids, glycoproteins.

• Example: Blood transfusions are type-specific due to these molecules.

selective permeability specifics

• Small nonpolar molecules (e.g., N₂, O₂, CO₂) → freely pass through the membrane.

• Hydrophilic substances (large polar molecules, ions) → move through embedded channels and transport proteins.

• Polar uncharged molecules (e.g., water) → pass through in small amounts.

passive transport

NO ENERGY (ATP) needed! Diffusion down concentration gradient (high 🡪 low concentration) Eg. hydrocarbons, CO₂, O₂, H₂O, primary role in the import of material and the export of wastes

osmosis

the net movement of water molecules across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration

isotonic

one with the same solute concentration as a cell's internal environment, leading to no net movement of water across the cell membrane and thus no change in cell volume or shape

hypertonic

one with a higher solute concentration outside a cell than inside, causing water to move out of the cell via osmosis, leading to cell shrinkage or crenation, means more solute concentration

hypotonic

one with a lower solute concentration (and thus a higher water concentration) compared to the inside of a cell, causing water to move into the cell via osmosis, which can lead to swelling or bursting (lysis) in animal cells., means less solute

facilitated diffusion

Transport proteins (channel or carrier proteins) help hydrophilic substances cross, Two ways: Provide hydrophilic channel, Loosely bind/carry molecule across, Eg. ions, polar molecules (H₂O, glucose)

aquaporin

channel protein that allows passage of H₂O

active transport

Requires ENERGY (ATP), Proteins transport substances against concentration gradient (low 🡪 high conc.), Eg. Na⁺/K⁺ pump, proton pump, think of bottom of hill to high

Glucose transport protein

carrier proteins that facilitate the movement of glucose across cell membranes via facilitated diffusion

Plasmolysis

the process where a plant cell loses water when placed in a hypertonic solution, causing the cell membrane to pull away from the rigid cell wall

Flaccid

the state of being soft and limp, lacking firmness or a rigid structure

Turgid

a plant cell that is swollen due to a high uptake of water through osmosis, causing the plasma membrane to push firmly against the cell wall

Wilting

the loss of turgor pressure in a plant's non-woody cells, which results in the drooping of leaves and stems and it causes for them to become flaccid

Hypotonic and plants and animal cells

Plant cell favors environment because it has a cell wall that can regulate, wall is strong and contains it and won’t expand, it won’t let an overflow and it will push back, creating a pressure in the plant that isn't in the animal,

Animal cells don't value hypotonic, blood cells burst, reason for IV to help regulate the water, cell membrane can’t

0 M vs 2 M

0 M solution will make the cell grow more than a 2 M solution where the cell is hypertonic because more must go into the cell for 0 M for equilibrium. In the 2 M less needs to be put in because there is less of a difference in hypertonic and hypotonic than in the 0 M solution

Electrogenic Pumps

generate voltage across membrane (na/k, and proton)

Na/ K pump

Pump Na+ out, K+ into cell, Nerve transmission, crucial for maintaining the cell's resting potential and electrochemical gradients, which are vital for nerve impulse transmission, muscle contraction, and nutrient transport.

Proton pump

Push protons (H+) across membrane, Eg. mitochondria (ATP production)

Cotransport

membrane protein enables “downhill” diffusion of one solute to drive “uphill” transport of other

Ex. sucrose-H+ cotransporter (sugar-loading in plants)

Passive transport

Little or no Energy, High 🡪 low concentrations, DOWN the concentration gradient, eg. simple diffusion, osmosis, facilitated diffusion (w/transport protein)

Active transport

Requires Energy (ATP), Low 🡪 high concentrations, AGAINST the concentration gradient, eg. pumps, exo/endocytosis

Osmoregulation

Control solute & water balance, Contractile vacuole, Eg. paramecium caudatum – freshwater protist

Contractile vacuole

“bilge pump” forces out fresh water as it enters by osmosis

Bulk transport

Transport of proteins, polysaccharides, large molecules, (endocytosis, exocytosis)

Endocytosis

take in macromolecules and particulate matter, form new vesicles from plasma membrane, (phagocytosis, pinocytosis, receptor-mediated endocytosis)

Exocytosis

vesicles fuse with plasma membrane, secrete contents out of cell

Phagocytosis

“cellular eating” - solids, a process in which a cell engulfs and internalizes large particles, such as bacteria, dead cells, or debris

Pinocytosis

“cellular drinking” - fluids, a type of endocytosis also known as "cell drinking" where a cell engulfs extracellular fluid and dissolved solutes to absorb nutrients and maintain homeostasis

Receptor-Mediated Endocytosis

Ligands bind to specific receptors on cell surface, a form of endocytosis in which receptor proteins on the cell surface are used to capture a specific target molecule

Water potential (ψ)

H2O moves from high ψ 🡪 low ψ potential

Pressure potential (ψP)

physical pressure on solution; turgor pressure (plants)

Solute potential

The addition of solute to water lowers the solute potential (more negative) and therefore decreases the water potential.

Where will water move

From an area of higher ψ 🡪 lower ψ (more negative ψ), low solute concentration 🡪 high solute concentration, high pressure 🡪 low pressure

Factors that impact the rate and direction of osmosis

size, temperature, charge

How is dialysis tubing different from a cellular membrane

dialysis tubing is made out of cellulose and diffusion and osmosis is regulated based on the size of solutes. The cell membrane has adaptations (protein channels and atp) that are used to move solutes that are too large or too charged to cross

When potatoes are in the ground do they swell with water?

They do not swell when it rains. They are the plant's energy reservoir and because it is a plant cell it has a cell wall that protects against these types of conditions. Instead the roots absorb excess water. Through capillary action, water potential, transpiration this water is moved up through the plant

Turgor pressure

• Turgor pressure is the pressure exerted by water inside a plant cell against its cell wall.

• It keeps plant cells firm and rigid, allowing plants to maintain their structure and stand upright.

• It results from water moving into the cell via osmosis.

Osmotic pressure

the minimum pressure required to prevent the flow of water across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration

Phospholipid bilayer

a two-layered structure that forms the basis of all cell membranes, composed of phospholipids with their hydrophilic (water-loving) heads facing outward and their hydrophobic (water-fearing) tails facing inward

Types of active and bulk transport

Endocytosis (phagocytosis, pinocytosis, receptor mediated), exocytosis

Integral proteins

proteins permanently embedded in the lipid bilayer of the cell membrane, perform transport and signal transduction, span the entire thickness of the membrane, interacting with the interior and exterior