Cell structure and function

cell theory

1. All living organisms are composed of one or more cells

2. The cell is the basic unit of life

3. All cells arise form pre-existing cells

Related research to abiogenesis

abiogenesis: creation of life without life (based on 3rd rule of cell theory)

Miller Urey experiment: primordial atmosphere/ocean in container, add electricity=biomolecules

Found 20 AAs and 5 nucleotide bases found in meteorites

RNa bases found in fast cooling lava

7 of life

1. Made of cells

2. Grow, develop, heal

3. Reproduce

4. Obtain and process energy (has metabolism)

5. Exchanges gases w/ the environment (respiration)

6. Has DNA

7. Responds to environment

8. Maintain consistent internal environments (homeostasis). Ie body temp, pH, osmosis, [O2], [Co2], [ion], [glucose] (all monitored by cell activity)

prokaryotic cells

smaller (0.5-5 micrometers), in bacteria and archaea, lack nucleus and membrane bound organelles,

Very abundant

First cells

All have cell wall

DNA in nucleotide region, have cell wall, plasma membrane, ribosomes, and flagella or puli for movement (tail thing)

Adapt to environment quick bc DNA is free floating and transcriptions and translation happen at same time and place. No membrane bound organelles so rats happen in cytoplasm, good for rapidly dividing

Eukaryotic cells

larger (10-100 micrometers), found in plants, animals, fungi, and protists; contain a nucleus and membrane-bound organelles, DNA organized into linear chromosomes.

DNA in nucleus: more complex gene regulation

Membrane bound organelles: good for complex rxts and effiency

Both Eu and Pro

DNA

Cytoskeleton

Ribosomes

Cytoplasm

Cell membrane

Specialized cells

Cell has specific function via differentiation to be different from progenitor cells (cells that preceded them-stem cells-Undifferentiated cell that has the ability to specialize)

Have different structure and organelles (amount, distribution, and type)

Nucleus

Hold cell DNA

Coordinate Growth, metabolism, reproduction

Nucleolus makes ribosomes

Double membrane

ribosomes

site of protein synthesis, either floating freely in cytoplasm or attached to rough ER

Rough endoplasmic reticulum

protein synthesis and modification, have ribosomes

Network of folded sacs and tubes

Smooth ER

synthesis of lipids and detoxification, lacks ribosomes

Golgi apparatus

modifies, Scotty’s, and packages proteins and lipids for storage or transport out of cell. Has flattened space called cisternae.

Cis side: receives vesicles from ER

Trans side: ships vesicles to final destination

Mitrochondria

generate ATP through cellular respiration

Double membrane structure: outer membrane and highly folded inner membrane called cristae, increases surface area for ATP

Has own DNA

Chloroplasts

photosynthese, light energy→chemical energy in glucose

A type of plastid

Double membrane

Thylakoids (stacked into grana): light dependent reaction occur

Granum: flat membrane stacks, increases surface area SA

Stromatolites: Calvin cycle bc of appropriate enzymes and suitable pH

Lamella:connects and separates thylakoid stacks

Has own DNA

Lysosomes

digestive enzymes that break down waste materials and cellular debris

Small spherical sacs

Peroxisomes

enzymes that detoxify harmful substances and break down fatty acids, producing hydrogen peroxide as byproduct, which is converted to water

Vacuoles

storage organelles

in plant cells: large central vacuole maintains turgor (internal h20 force on membrane) pressure which helps maintain the plants structure and rigidity

Animal cells: smaller vacuoles store various substances

Cytoskeleton

structure, aids in cell division, enables cell movement

Microfilaments: thin actin filaments that support cell shape and enable movement

Microtubules:hollow tubes made of tubular that help with cel shape, transport within cell, and cell division

Intermediate filaments: fibrous proteins that provide mechanical support and help maintain cell shape

Plant cell walls

Support and protection, maintain cell shape, provides rigidity, prevents excessive water uptake

Made of cellulose fibers embedded in matrix of other polysaccharides and proteins

Prevents bursting in hypotonic (lower solute concentration and lower osmotic pressure than another fluid) environment by providing a counter pressure

Path of protein in cell

M mRNA is transcribed in nucleus, leaves to ribosomes (where protein is synthesized, mRNA translated) on RER for modification (fold and process), then travels in RER to SER then Golgi apparatus for packages and sorting. Then leaves through a vesicle to final destination (cell membrane, outside cells, lysosomes, or stay in ER)

Endomembrane system

organelles involved in synthesis, modification, and transport of proteins and lipids

Consists of nuclear envelope, rough and smooth ER, Golgi apparatus, lysosomes, vesicles, and plasma membrane

Ensures that cellular products are properly processed and directed to their destinations

Energy organelles

mitochondria and chloroplasts

Involved in energy conversion

Compartmentalization

the division of cellular functions into distinct membrane bound organelles (in eukaryotic cells), allowing for specialization and for specific biochemical rxts to occur i isolated areas, enhancing efficiently in processes like metabolism and protein synthesis.

Lysosome compartmentalization

acidic environment is optimal for enzyme activity, preventing damage to other cellular components

Mitochondria compartmentalization

inner membrane (cristae): large surface area for electron transport chain

Mitochondrial matrix: enzymes for Karen’s cycle enabling efficient ATP production

Difference between plant and animal cells

Plants: cell wall, chloroplasts, large central vacuole, plasmodesmata(channels that allow communication and transport between plant cells). 10-100 micro meters, rectangular or cubic shape

Animals: lysosomes, centrioles ( cell division), cilia and flagella (movement). 10-30 micrometers, rounde or irregular shape

Similarities plant cell and animal

cells: both have cell membranes, golgi, cytoplasm, mitochondria, and a nucleus. They also share ribosomes and endoplasmic reticulum for protein synthesis.

Also both are eukaryotic

Cell metabolism

Chemical reactions that occur in a cell to maintain life.

Breaking down nutrients for energy, synthesizing proteins, and removing waste products

Effeciency of metabolic processes are influenced by the cells size

Small cells have a

Higher surface area relative to their volume SA:V which is more efficient for exchanging materials and distributing nutrients, which supports higher metabolic rates

SA:V

high SA:V is beneficial for exchanging materials quickly and efficiently through diffusion

Cells can lose heat more rapidly with a high SA:V ratio, helping to maintain optimal temps for enzymatic activities

Formulas for SA and V

Cuboidal cells: SA=6s² V=s³

Spherical cells: 4 pi r² V=(4pi r³)/3

S=side length

R=radius

As the size (side length for cubodial or radius for spherical) increases

the volume grows faster than the surface area, causing a decrease in SA:V ratio

Larger cells struggle to obtain enough nutrients and oxygen or to expel waste quickly

Reduced SA ration can hinder cells ability to support high metabolic activity, affecting growth and reproduction

Strategies to increase SA:V ratio

Microvili, flattened shapes, and compartmentalization (all increase surface area relative to volume)

Plasma membrane (cell membrane) functions

protection, support, controls what enters and leaves cell (selectively permeable), Maintains homeostasis

Plasma membrane structure

Phospholipid bilayer: tails face inward shield from water, heads face outward toward aqueous environment

proteins: integral (penetrate hydrophobic core of bilayer, channels or transporters for molecules) and peripheral (exterior or interior surfaces of membrane, signaling or maintain shape)

Aquaporins: protein channel increases diffusion rate of water

Carbohydrates: attached to proteins (called glycoproteins) on extra cellular side for cell recognition and communication, help cells identify each other and interact. ( also lipids attached to proteins called glycolipids help)

Lipid insoluble

polar

Fluid mosaic model

plasma membrane structure is a mosaic of various proteins that float in or on the fluid lipid bilayer, also lipids and carbs arranged in mosaic patternt

fluidity: the lipid bilayer is flexible, allowing lipids and proteins to move laterally within the layer

Factors affecting membrane fluidity

temperature: higher temp increases fluidity, lower temp decreases it

Fatty acid composition: unsaturated fatty acids increase fluidity due to kinds in their tails, saturated fatty acids decrease fluidity

Cholesterol: at high temps it stabilizes membrane and reduces fluidity. Low temps prevents tight packing of phospholipids increasing fluidity

Easy vs difficult to diffuse

Easy: small, non polar molecules like oxygen and carbon dioxide and N2

Hard: large (glucose, lipids, proteins) polar molecules (H20 get stuck but sometimes diffuse, polar head is attracted, and ions (Na+, Cl-, K+, Fl-, Ca2+, Mg2+, Li+)

Passive transport

Movement of substances across membrane without use of energy

Simple diffusion, osmosis, and facilitated diffusion

Simple diffusion

Solutes move from area of high concentration to low concentration until they are evenly distributed, happens naturally does not require energy

Osmosis

Solvent moves from area of lower solute concentration (more water) to higher solute concentration (less water)

Maintaining cell homeostasis, ensuring that cell neither swell excessively nor shrink too much, which can disrupt function and lead to cell death

Facilitated diffusion

Use proteins to help larger or polar molecules cross membrane, the proteins are hydrophobic so they are able to embed into plasma membrane

Channel proteins: from pores in membrane, allow specific molecules or ions to pass (ex aquaporins: rapid passage of water)

Carrier proteins: bind to the molecule they transport, change conformation, and release the molecule on the other side

Active transport

requires atp to move substances against concentration gradient low→high

Sodium potassium pump

three sodium ions out and two potassium ions into the cell using 1 molecule of ATP

Maintain the cells membrane potential, an electrical gradient across membrane

Found in almost all animal cells and is common in plant cells too

Sodium must be removed from cell to maintain fluid balance

Gradient can be use to drive transport of other substances like cotransport of glucose.

Proton pump

moves protons (H+ ions) out of the cell, creating gradient for ATP synthesis in cellular respiration

Inside is negative, potential difference can be couples to the transport of other molecules

Cotransport

simulatneous movement of two substances across membrane. Proteins moves one substance down its electrochemical gradient in order to move another substance against its concentration/electrochemical gradient

Symport: both substances move in same direction

Antiport: substances move in opposite directions

Plants: sucros-proton con transport system uses proton gradient created by proton pump to bring sucrose into the cell against its concentration gradient

Ex. Gradient in sodium ions drives transport of glucose intestinal epithelial cells,

Plasmolysis

The process where plant cells lose water in a hypertonic solution (osmosis), causing the cell membrane to pull away from the cell wall.

Dynamic equilibrium

concentrations are equal on either side of membrane but molecules are still in motion

Endo and exotytosis

move large molecules/particles in or out of cell using vesicles

Active transport

Through localized activity of micrtofilaments and microtubules in cytoskeleton

Exocytosis

Cells expel materials by merging vesicles with the plasma membrane, releasing their contents outside the cell.

Used to secrete hormones, neurotransmitters and digestive enzymes

Typical of secretory cells

Ex. lymphocytes secrete proteins out

Endocytosis

cells take in materials by engulfing them in a vesicle formed by the plasma membrane

Typically in protozoans and white blood cells

Phagocytosis: cell eating-cell engulfs large particles (solid) like food, pathogens, and cellular debris to form vesicles. Ex capture and destruction of a bacterial cell by white blood cell, or ingestion of a food particle by a protozoan

Pinocytosis: cell drinking-cell takes in extra cellular fluid and dissolved substances to form pinocytic vesicles. Cell membrane encloses and forms vesicle, the fuses with lysosome to break substance down. Ex uptake of extracellular fluid by liver cells, Receptor-mediated endocytosis: specific molecules are taken into the cell after binding to receptors on the cell surface, forming a vesicle around the bound molecules

ATP in active transport

broken into ADP and phosphate group, and energy is released

Tonicity

Ability of a surrounding solution to cause a cell to gain or lose water. Determined by the relative concentrations of solutes inside the cell compared to outside

Hypo,hyper,isonic

Isotonic solution

solute concentration is equal inside and outside the cell

Ex. When cell in in saline solution with same concentration as its cytoplasma, water moves in and out of cell at equal rates

Hypotonic solution

solute concentration outside the cell is lower than inside the cell

Ex. Cell is in pure water, water enters the cell due to osmosis, causing cell to swell and possible burst (lysis)

Plants: cells become turgid (firm) due to inflow of water, idles for structure

hypertonic solution

solute concentration outside the cell is higher than inside the cell.

Ex. Cell in a saltwater solution, water leaves the cell, causing it to shrink.

Plants: lose water, plasma membrane pulls away from cell wall, (plasmolysis) can be damaging

Cyclosis

Movement of cytoplasm in a cell to distribute nutrients

Water potential

Ψ

Measure of potential energy in water and is used to predict the direction of water movement.

Water moves from regions of higher water potential to regions of lower water potential,

Water potential will be equal to the solute potential for

a solution in an open container because the pressure potential of the solution in an open container is zero

water potential formula

Ψ=Ψp + Ψs

ΨP=pressure potenital

ΨS=solute potential

Solute potential

Ψs, also osmotic potential

Effect of solute concentration on the water potential. It is always negative or zero b/c addition of solutes lowers the water potential

Solute potential formula

Ψs= -iCRT

I=ionization constant (the number of particles the solution dissociates to)

C=molar concentration of the solute

R= pressure constant (0.0831 liter bar per mole K)

T= temp in Kelvin

Pressure potential

Ψp

The physical pressure exerted on or by the cell. In plant cells: positive due to turgor pressure form the cell wall, which helps maintain rigidity