Cell

• basic units of life

• example of Emergent Properties → organelles put together inside a cell membrane → life emerge

• Prokaryotic cells: eubacteria and archae

  • evolved before the evolution of the nuclear membrane and nucleus

  • lack membrane bound organelles

  • have ribosomes

  • extremely small

• Eukaryotic cells:

  • evolved after the evolution of the nucleus

  • membrane bound nucleus and membrane bound organelles

Endosymbiotic Hypothesis

• hypothesized that some prokaryotes begin to live together in symbiotic relationships

• smaller prokaryotes living inside larger ones

• higher survival chance → evolved into Eukaryotic cells

Survival Advantage

• smaller organisms gained protection

• larger organisms gained energy production or faster motility

• swapped DNA segments (genetic annealing) → more permanent existence

• smaller became membrane bound organelles

Evidence

• found in mitochondria and chloroplasts

• have their own single circular chromosome like bacteria

• similar ribosomes to those found in bacteria

• able to independently reproduce within large eukaryotic cells (similar process with binary fission)

• phagocytosis of original symbionts → a double (phospholipid bilayer) cell membrane

Surface area to Volume

• Cells grow → ratio decreases while demand for internal resources increases

• cell gets larger → harder for cells to transport it and out

• trasnport of nutrients/wastes

• determining the rate of heat exchange between organisms and its environment

Adaptions to increase:

• folds inside the mitochondria

• flat pancake-like structures inside chloroplasts

  → greater area surface area for specific ractions

• folds in the lining of stomachs/tiny cellular of small intesine (villi and microvilli)

  → increase the surface area without increasing the overall size/volume

Prokaryotes

• unicellular

• 3 basic shapes: cocci (round), bacilli (rod), helical (spiral)

Structure:

• single circular chromosome: not enclosed in a nuclear membrane

• ribosomes: making proteins

• cytoplasm: DNA floats in the cytoplasm → nucleoid

• cell wall: protection of the underlying cell membrane + prevent bursting in an aquatic environment. (eubacteria composed peptidoglycan (protein and carbohydrate)

• no membrane-bound organelles

• have specific internal regions with specialized structures and functions

Gram positive and Gram negative

• capsule: adherence to surfaces + protect the bacteria from a host cell’s immune response

• most bacteria benefits: decomposition/mineral cycling, fix nitrogen, photosynthesis, manufacture certain food and chemicals

Eukaryotes

Overview:

• larger and more complex than bacteria

• nucleus, complex organelles, cytoskeleton:

  1. plasma cell membrane: hold cell together (similar to prokaryotes)

  2. nucleus: controls activities by holding DNA (enclosed within nuclear membrane/envelope)

  3. cytoplasm or cytosol: fluid filled space → makes up most volume

  4. membrane-bound organelles: enclosed tructure for specific jobs → more efficient

Structure

Cell/plasma membrane

• establish + maintain internal environments

selectively permeable:

allows/ actively transports certain materials into/out of the cell while not allow others

→ small + nonpolar substances (N₂, O₂ and CO₂) → enter easily

→ small + polar (H₂O) can pass in small amount

→ large/polar charged substances → can’t enter or by protein channel

phospholipid bilayer:

• makes up majority of cell membrane and organelle membranes

Amphipathic:

• both hydrophobic and hydrophillic

  → hydrophillic (phosphate group): toward the water both inside and outside the side

  → hydrophobic (fatty acid tails): toward each other in the center of the membrane. One saturated fatty acid and one unsaturated (kink)

Proteins:

• different types are embedded:

  • hydrophillic with charged and polar side groups

  • hydrophobic with nonpolar side groups

• Integral proteins: run through the bilayer (outside to inside) → transport of molecules across the membrane + maintain the integrity of the membrane

• Peripheral proteins: on one side of the membrane (not extend through the bi-layer) → receptors for cell signals, catalysts/enzymes, structural components of the cytoskeleton

• Functions:

  • molecule transport

  • enzymes

  • cell to cell communication and recognition: helps cells attach to each other to work/communicate

  • signal receptors: receive hormones/other signaling molecules circulate in blood/interstitial fluids

  • attachment points: for the cytoskeleton

Cholesterol

• Functions:

  • keep membrane from being too fluid/permeable to some small molecules

  • secure proteins embedded in the membrane

  • keep plant cells from freezing solid

• Fluid Mosaic Model: phospholipids compose the fluid, proteins embedded within like a mosaic

The Nucleus

• control center for all activities

• source of the cell’s genetic information (DNA)

Nuclear Envelope

• mainly a double phospholipid bilayer

• encloses DNA

• has pores (tunnels) made of proteins → allow certain materials enter/exit

  E.g: mRNA exit the nucleus and go to ribosomes to act as the directiosn for making proteins

DNA

• chromatin phase: most of cell’s cycle, DNA loose and spread out

  → can be transcribed and used to make proteins

• chromosome phase: DNA coils around histones (proteins)

  → help to organize the DNA → it can be corrected distributed during nuclear and cell division

Nucleolus

• dark spot within the nucleus

• Functions: make rRNA and proteins which make up ribosomes

Ribosomes

• cell particles made of rRNA and proteins

• not enclosed within a membrane

• reflects the common ancestry of all living things

• sites of Protein Synthesis

• 2 types of ribosomes: free and bound

Free Ribosomes

• float freely in the cytoplasm (All types of cells)

• make proteins that will stay and function inside the cell that made them

Bound Ribosomes

• attached to the Rough endoplasmic reticulum (RER)

• make proteins that leave the cell → act as cellular communication signals/antibodies to fight infactions

Endomembrane system

Compartmentalization

• compartmentalize/partition/divide the cell into distinct locations → specific intracellular metabolic processes and enzymatic reactions

• internal membranes + partitioning → minimize competing interactions + increase the surface area for reactions

Overview

• group of membranes and organelles in eukaryotic cells working together → modify, package, transport lipids and proteins

• bound ribosomes make proteins → proteins enter rough ER → packaged into phospholipid-based secretory vesicles → vesicles transport the proteins to Golgi apparatus → modifying porteins → packaged into lipid based vesicle → cell membrane

  → proteins excreted from the cell and vesicle’s phospholipid becomes part of cell membrane

Process

• vesicle buds from smooth/rough ER

• vesicle fuses with Golgi apparatus, dumping contents inside

• Golgi modifies molecules (as they move through successive chambers)

• Modified molcules bud off from Golgi (as transport vesicle)

• vesicle fuses with the plasma membrane → dumping contents outside for delivery

Endoplasmic Reticulum

Smooth Endoplasmic Reticulum (Smooth ER)

• helps with the synthesis of lipids, phospholipids, and steroids

• helps with carbohydrate breakdown

• aids the detoxification of the blood (liver cells are loaded with SER)

• storage of Ca⁺⁺ needed for muscle conteaction (muscle cells have lots of SER)

Rough Endoplasmic Reticulum (Rough ER)

• helps with protein synthesis, modification, and transport

• ribosomes are bound to the outside of the organelle and deposit the newly constructed proteins into the Rough ER

• proteins are folded into 3-D structure needed to function inside the structure

• functions to compartmentalize the cell → scpecialization and division of labor

Golgi Apparatus

• sereies of flattened membrane sacs

• modifies proteins by attaching sugars to them → Glycoproteins → determine proteins’ function and final destination

  → glycosylation

• warehouse for storage of proteins → packages proteins and ships them out in vesicles

• near the cell membrane

Lysosomes

• conatin hydrolyic enzymes + acids

• process of intracellular digestion → breakdown materials within a cell → be recycled for other purposes

• destruction of old cells that are undergoing apoptosis (programmed cell death)

Mitochondria

• “Power House”

• perform aerobic cellular respiration

• energy from food → bonds of ADP and P → ATP

• has its own DNA, bacteria-like ribosomes, and enzymes → even reproduce independently via membrane

• outer phospholipid bilayer is smooth

• inner layer are folded into cristae → increase surface area and serve as sites for the electron transport chian

• 2 membranes provide compartments where specific metabolic reactions can take place

Evolutionary Significance

• descended from aerobic bacteria that entered into a symbiotic relationship with a larger prokaryote cells

• survive and reproduce and eventually led to the evolution of Eukaryotic cells.

Choloroplasts

• sites of Photosynthesis in plants and algae

• type of Plastid or pigment container

• own DNA, ribosomes, and enzymes.

• Reproduce indepently via binary fission

Structure:

• thylakoid: stacks of sack-like structures

• grana: stacks of thylakoid

  → increase the surface area needed to carry out light-dependent stages of photosynthesis

• pigments and electron transport proteins required for the light dependent stage of photosynthesis are embedded within the membranes of the thylakoids.

• stroma: mostly watery space between thylakoids and outer membrane; site of the Calvin Cycle (metabolic pathway producing sugar)

Evolutionary Significance

• may evolve from blue-green bacteria (cyanobacteria) that entered into a symbiotic relationship

• protection in return for sugar production

Cytoskeleton

• support and protect cell

• keep inner organelles organized

• make up structures such as flagella and cilia →aid in cell motility or cell organelle movement

• composed of various sized protein fibers known as microtubules, microfilaments, or intermediate filaments

Cell Walls

• provide structural boundary, permeability barrier for some substances

• Plant cells: composed of cellulose → support and protection, prevent from bursting

• Fungus: composed of chitin → similar to plant cell

Extracellulat Matrix (ECM):

• molecules are secreted into the space out the cell's membrane → form cell walls, bone, cartilage,…

• provide support, to segregate different tissues from one another and regulate intercellular communication

Material Transport

• growth and homeostasis are maintained by the constant movement of molecules across the membranes

Passive Transport

- doesn’t require cell to use its own metabolic energy

- powered by energy (heat) from the environment

Diffusion

• operate upon established concentration gradient or difference in concentration

• flow from high → low concentration until equilibrium

• non-polar and small particles (CO₂ and O₂)

• used mostly by cells to save energy

Osmosis (diffusion of water)

• high → to low water concentration

• low → high solute concentration

• tonicity: ability of an extracellular solution making water move into or out of cell

• osmolarity: total concentration of all solutes in the solution

• low osmolarity: fewer solute particles

• hypotonic: low solute concentration

• hypertonic: high soluter concentration

• isonic: equal

• most H₂O movement occurs through proteins aquaporins

=> control internal solution composition/ water potential; main functions of the urinary system

• turgid: lots of water in a cell, rigid and stiff

• flaccid: not very much water in cell, limp and wilted

• Plasmolysis: shrivels away from cell wall (placed in hypertonic solution)

Water potential

• high to low water potential

• total water potential of pure water in an open container is 0

• ionization constant: number of ions formed when dissolved (ions only, no covalent)

• higher solute potential → lower water potential

• higher pressure potential → higher water potential

Facilitated Diffusion

• transport materials from high to low concentration

• requires channel or transport proteins because those are either polar/ionic/large.

• aquaporins: move water

• Gated-ion channels: move Na+ and K+ ions

Active transport

• requires metabolic energy by the cell provided by ATP Hydrolysis

• moves materials against the concentration gradient

Na+/K+ Pump

• of the nervous system: has an ATPase enxyme assosiated with it → enzyme catalyzes hydrolysis of ATP → provide energy needed for transport

  => Movement of ions can cause the membranes of certain cells (neurons) to become polarized (1 positive side and 1 negative side)

• Energy from ATP by Phosphorylation (attaching a phosphate ion to a structure to activate it) activate the protein to grab and move molecules

Electrogenic Pump (aka Proton H⁺ Pump)

• most important active transport

• involved in the electron transport chain of photosynthesis and cellular respiration

• H⁺ move out of cell to create a gradient (outside is +, inside is -)

• diffusion now occur based on charges into and out of cell → gradient sereves as source of energy for producing ATP

Co-transport

• 2 substances are simultaneously transported across a membrane by one protein, or ptrotein which not have ATPase activity

• 1 of the substances moves with the gradient → provides energy to transport other substances against the gradient

• symport: both substances are transported same way

  • absorption of glucose by epithelial cells in gut

  • glucose is co-transported with Na⁺ ions

  • Concentration of Na⁺ions is higher outside the cells than inside → Na⁺/K⁺ pump maintain the sodium concentration: primary active transport

  • Na+ moves into cells down its concentration gradient → energy powers secondary active transport of glucose into cells (against gradient)

    

• antiport: substances are transported in opposite directions

Large Molecule transport/ Bulk transport

• movement of too big molecules for protein

• require expend metabolic energy

Endocytosis

• into cell

• Phagocytosis

  • large, solid particles

  • surrounding of the particles with the cell membrane → engulfing of the particles → surrounding the particles with a vesicle

  • E.g: white blood cell taking in a bacterial cell

  • usually followed by the process of intracellular digestion

• Pinocytosis

  • small particles suspended in extracellular fluid brought into cell

  • through an invagination of the cell membrane → suspension of the particles within a small vesicle

  • then fuse with lysosomes to break down the particles

• Receptor mediated endocytosis

  • specific molecules are transported into the cell

  • a receptor-ligand interaction

  • ligan is a substances being transported into cell

  • ligand binds to a receptor → triggers an endocytotic process and the ligand is ingested