Cell structure and function

The cell

  • the need for a boundary (cell membrane)

  • the need for DNA (the blueprint)

  • the need for energy (the fuel): ATP

Prokaryote vs Eukaryote

  • Prokaryote - these are cells that existed before the nucleus

    • bacteria cells

    • DNA is in the nucleoid

    • have a single circular naked DNA

    • lake any membrane bound organelles

    • have a cell wall but are different in composition to the cell walls of eukaryotes

    • ribosomes are small

  • Eukaryote - these are cells that have a true nucleus

    • plant animal fungal cells and protists

    • most of the DNA is in the nucleus which is bounded by a double membrane

    • genetic materials is found in chromosomes (DNA + proteins)

    • including membrane bound organelles

    • ribosomes are larger

PLANT VS ANIMAL

Nucleus Structure

  • double membrane (nuclear envelope) with pores

  • Functions: stores DNA (genetic info)

  • ribosome synthesis (nucleolus)

Rough Er (Endoplasmic Reticulum)

  • Structure - membrane attached with ribosomes attached to nuclear envelope

  • Functions:

    • site of membrane bound protein, enzymes and secreted protein synthesis

    • role in intracellular transport

Smooth ER

  • Structure - folded tube like (cisternae)

  • functions - detoxification

  • calcium storage

  • lipid synthesis

Golgi Complex

  • Structure - membrane bound structure composed of flattened sacs(cisternae)

  • Functions - folding and chemical modification of synthesized proteins

  • packaging protein traffic

Ribosomes Structure

  • Structure - composed of rRNA and protein

  • large and small subunits

  • types: bound or free (cytoplasmic)

  • Function: protein synthesis

Vacuole structure

  • Structure - membrane bound sac

  • Function - storage and release of macromolecules and cellular waster products

  • central: water retention - turgor pressure

  • Contractile: osmoregulation (protist)

  • Food: phagocytosis fuse with lysosome

Lysosome

  • Structure - membrane enclosed sacs that contain hydrolytic enzymes

  • Functions: intracellular digestion (recycle cell organic materials and programmed cell deal: apoptosis)

Mitochondria

  • Structure - double membrane (out smoother, inner, highly folded)

  • Functions - site of krebs cycle (matrix), site of oxidative phosphorylation (cristae/inner membrane)

Chloroplast

  • Structure - double outer membrane(thylakoid sac stacked: grana and fluid: stroma)

  • Functions - site of photosynthesis

  • Thylakoid - light reactions

  • Stroma - Calvin Benson Cycle

Cell Wall

  • structure and protection

  • made of cellulose

  • chitin for fungi

  • prokaryote pepitodoglycan

Most favorable cell is one with larger surface area/volume ratio

  • how can a cell increase surface area without increasing volume? Microvilli

  • How does an increase in surface area affect heat exchange

    • larger surface area = more heat exchange with environment, lose more heat

Plasma Membrane

  • phospholipd bilayer

  • proteins

  • cholestrol

  • Carbohydrate chain

    • lipid - glycolipid

    • protein - glycoprotein

FLUID MOSAIC MODEL

Cholesterol helps maintain fluidity, stability, and intergrity

Membrane Permeability

  • the cell membrane is nonpolar

  • pass through directly

    • small nonpolar molecules

  • Pass through with requirement:

    • charged particles

    • and polar molecules

  • For big materials

    • Exocytosis

    • Endocytosis

Passive Transport

  • simple diffusion - no transport protein needed

  • facilitated diffusion - requires a transport protein (ex. channel, carrier)

    • transport charge particle or polar

  • Molecules move from a high concentration to a low concentration

● No ATP energy required

Active Transport

Exosytosis/endosytosis

Channel proteins

  • Hydrophilic region in the interior

  • allows solute to pass through

  • small amounts of water can diffuse through the membrane directly without aquaporins

Carrier Proteins

  • integral membrane that facilitates the movement of specific molecules across the cell membrane by binding to the substance and undergoing a conformational change

Active Transport - molecules move from low to high concentration, needs ATP energy and transport protein, charge or polar particles

  • two ways to get energy

    • transport protein hydrolyzes ATP to ADP +Pi to get energy

    • Transport proteins do not use ATP directly, but relies on energy stored in an ion gradient

Endosytosis and Exocytosis

  • both need Atp energy

  • exocytosis - molecules exit the cell using the vesicle

  • Endocytosis - molecules enter the cell through the creation of vesicles

    • phagocytosis: the cell membrane reaches outward and engulfs food in the vesicles then fuse with lysosomes for digestion

    • Pinocytosis: the cell membrane folds inward to pull fluids into the cell

    • Receptor-mediated endocytosis: ligands bind to receptor to cause the pit and form a vesicle

Osmosis - process involving the movement of solvent through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration

Osmoregulation - maintenance by an organism of an internal balance between water and dissolved materials regardless of environmental conditions.

Hypotonic solution: lower solute concentration in a high amount of water

Hypertonic solution: higher solute concentration in a low amount of water

Isotonic solution: Isotonic refers to a solution with the same solute concentration as another solution

Water potential (Ψ) is a measure of the potential energy of water — basically, it tells us which way water will move.

Water always moves from higher water potential → lower water potential, just like how objects roll downhill.

Ψ = ΨS + ΨP

Ψ = water potential

ΨS = pressure potential

ΨP = solute potential

Ψs = -iCRT

i=ionization constant

C=molar concentration

R=pressure constant, 0.0831

T=temperature in Kelvin (°C+273)

Membranes compartmentalize the cell, creating distinct, controlled environments where specific processes can take place efficiently and without conflict.

Eukaryotic cells are larger because they have membrane-bound

organelles. That compartmentalization let them organize and

sustain more complex life functions.

What is the function of the inner membrane folding in the

mitochondria?

What is the function of the endoplasmic reticulum’s folded

membrane?

Rough ER: Provides distinct reaction spaces for

protein.

Smooth ER: Calcium storage. Provide distict region for

lipid synthesis.

The structure supports ATP synthesis, where

protons flow through ATP synthase to power ATP

production.

Compartmentaliztaion

What is the function of the thylakoid membrane in the

chloroplast?

The light-dependent reactions to occur inside the

thylakoid membrane.

A proton gradient to build across the membrane for

ATP synthesis.

What is the function of the multiple membranes and sacs found in

the Golgi?

Each compartment modifies them in a specific order

(adding sugars, tagging for transport).

This ensures proper sorting and packaging before

they exit the cell.

Eukaryotic cells likely evolved

when a larger prokaryote

engulfed smaller bacteria,

forming a mutually beneficial

partnership that became

permanent — giving rise to

organelles like mitochondria

and chloroplasts.

Mitochondria come first.

● Reproduction — They divide independently by binary fission, like

bacteria.

● Own DNA — Mitochondria and chloroplasts have circular DNA, like

bacteria.

● Ribosomes — Similar to bacterial ribosomes (70S type).

AP BIO PENGUINS

Ribosomes

composition - ribosomal RNA (rRNA) and protein non membrane, subcellular structures

Role - synthesize proteins according to messenger (mRNA) RNA sequences

Found - in cells in all forms of life and reflect the common ancestry in all known life

Endoplasmic Reticulum:

Role: provides mechanical support to maintain shape and intracellular transport

Rough ER:

  • compartmentalization

  • protein synthesis (membrane bound ribosomes)

Smooth ER:

  • detoxification of cells

  • lipid synthesis

Golgi Complex

  • membrane bound structure with series of flattened membrane sacs

  • materials from rough ER

  • Role:

    • correctly fold and chemically modifying newly synthesized cellular products

    • packaging proteins for trafficking

    • moves through cisternae (folds)

Mitochondria

  • Role: provide compartments for different metabolic reactions involved in aerobic cellular respiration

  • inner membrane (cristae) is highly folded to help ATP be synthesized more efficiently

  • has own circular DNA and own ribosomes

  • double membrane (inner is cristae, highly folded)

  • krebs cycles (matrix) and oxidative phosphorylation (cristae/ inner membrane)

Lysosomes

  • membrane enclosed sacs with hydrolytic (water breaks own) enzymes

  • role: intracellular digestion

  • apoptosis

Vaculoses

  • membrane bound cells

  • role: central Vacuole maintains turgor pressure with nutrient and water storage (plant cells)

  • contractile vacuole maintains osmoregulation in some single celled organisms (pumps water out so it doesn’t burst)

  • food vacuole formed from phagocytosis and fuses with lysosome

  • smaller in size in animal cells and more plentiful than in plants

chloroplast

  • 2-3 membranes (thylakoid - light reactions)

  • specialized organelles that are found in plants and photosynthetic algae

  • own circular DNA + ribosomes

  • location for photosynthesis

Membrane Bound Organelles

  • compartmentalize cells intracellular metabolic process and specific enzymatic reactions (no ribosome b/c they don’t have membrae)

Internal Membranes

  • facilitate cellular processes by minimizing competing interactions and increases surface area where reactions occur

  • mitochondria: Cristae - oxidative phosphorylation

  • Chloroplast: Thylakoid - light reactions

Cell Size

  • Sa/V

  • LARGE SA, small volume

  • obtains nutrients

  • eliminate waste products

  • acquire/dissipate heat

  • exchange chemicals/energy with environment

  • SMALLER CELLS HAVE HIGHER SA/V and more efficient exchange of materials with environment (metabolism more frequently b/c loss of heat)

Plasma Membrane

cell walls - barrier for substances and prevent osmotic lysis (bursting)

Simple diffusion

  • passive transport, no energy/transport protein

  • down concentration gradient

  • SMALL NONPOLAR

  • small amount of polar uncharged molecules leak through membrane (H2O)

Facilitate Diffusion

  • passive transport, no energy

  • down concentration gradient

  • small molecules

  • requires transport proteins (channel vs. carrier)

  • ex. H2O, Na, etc,

  • Membrane becomes polarized due to movement of ions

  • aquaporins transport large quantities of water across membranes

Active transport

  • requires energy

  • against concentration gradient

  • requires transport protein Na/K pump and ATPase

  • maintains membrane proteins

Membrane Transport

Exocytosis - internal vesicles release material from cells by fusing with the plasma membrane and secreting large molecules from cell

pathway: Rough ER (synthesize), Golgi (package/modification), transport vesicle, plasma membrane

Endocytosis - takes in large molecules and particulate matter by folding the plasma membrane in on itself and forming new small vesicles that engulf material from the external environment.

Tonicity and Osmoregulation

  • always compare hyper to, hypo to

  • Hypotonic Solution - low solute concentration, high free water concentration, loses water to hypertonic solution

  • Hypertonic solution - high solute concentration, low free water concentration, gains water from hypotonic solution

  • Isotonic Solution - equal water and solute (in and out)

Water potential

Hypotonic cell

  • low solute concentration

  • high free water concentration

  • loses water to hypertonic solution

hypertonic

  • higher solute concentration

  • low free water concentration

  • gains water from hypotonic solution