Cell Basics

• A cell is a group of organelles and molecules working together to perform a specific task and help the organism maintain homeostasis

• Living organisms must have at least one cell

• Two types of cells

  • Prokaryotes

  • Eukaryotes

• Why cells are so small-Surface to volume ratio: As cell gets bigger its volume increases faster than its surface area

• Limits to cell size-Metabolic requirements set upper limit: As cells gets larger, moving material in and out of the cell fast enough to support life is difficult

• How to get bigger?-DIVIDE: Become multicellular or… divide

• Prokaryotes vs. Eukaryotes

  • Prokaryotic Characteristics:

    • Bacteria and Archaea

    • Single Celled ONLY

    • No nucleus

    • No membrane bound organelles

    • Smaller and simpler cells

    • Oldest cells

  • Eukaryotic Characteristics:

    • Plants, animals, fungi, protists

    • Single celled or multicellular

    • Have a nucleus

    • Have membrane bound organelles

    • Larger and more complex

    • Evolved from prokaryotic cells

  • Shared Characteristics:

    • Both pro and eu have

      • Genetic material(DNA/RNA)

      • Cell membrane

      • Ribosomes

    • Some pro and eu have:

      • Cell walls

      • Flagella

    • Both use cellular respiration to make ATP

    • Cell Characteristics:

      • All Cells have:

        • Plasma membrane

        • Have cytosol

        • Chromosomes in form of DNA

        • Ribosomes

• How big is a cell: Cells can be anywhere between 10 micrometers to 1 mm in range

  • Cells have to be big enough to fit all the DNA and organelles, but also be small enough to efficiently exchange nutrients, oxygen and waste with the extracellular environment to maintain homeostasis

• Cell Shape and Function:

  • A cells shape and the amount of organelles it has determines the function of the cell

    • Sperm cells have long flagella and mitochondria because they need to swim toward the egg

    • Plant cells have a cell wall and are square so they can stack and give the plant structure

• Types of Organelles

  • Non-membrane bound: Organelles that do not have their own membrane inside of the cell

    • Ex: Ribosomes, cell membrane, cell wall, cytoplasm

  • Membrane bound: Organelles that have their own membrane inside of the cell

    • Ex: Nucleus, Vacuole, Mitochondria, Chloroplast, Golgi, Endoplasmic Reticulum

• Why are membrane bound organelles important

  • Membrane bound organelles compartmentalize different areas of the cell, allowing those areas to have different conditions

  • This allows for specialization of different areas in the cell to do different jobs and concentrate enzymes and substrate in the same physical area

  • Organelles are usually folded to increase surface area

  • Increased surface area is important because it gives more real estate for important reactions/ enzymes to exist without making the organelles too big

  • More specialization=more complex life

• Endosymbiotic Theory:

  • Eukaryotic cells evolved after a large ancestral prokaryotes ingested mitochondria and chloroplast-like proto-prokaryotes and formed a close mutual relationship with them

    • Ancestral prokaryote became able to survive in the increasingly oxygen-rich atmosphere

    • Proto-prokaryotes got resources 

Endomembrane System

Non-membrane bound organelles

• Cell Membrane

• Cell Wall

• Ribosomes

• Cytoplasm

• Cytoskeleton

• Centriole and Spindle Fibers

• Flagella

Cell Membrane

• Phospholipid bilayer

• Regulates what comes in and out of of the cell and protects the cell interior from the extracellular space

Cell Wall

• Rigid structure made of complex carbohydrates found in plants, fungi,. And bacteria

• Provides structure for cells as well as acting as a permeability barrier for some substances to the internal environment

Ribosomes

• Found in all living organisms

• Composed of protein and ribosomal RNA(rRNA)

• Ribosomes “read” messenger RNA(mRNA) to synthesize proteins

• Can be found

  • Attached to rough ER

  • Free floating in the cytoplasm

Cytoplasm

• Liquid made primarily of water and salt and other dissolved nutrients in the cell

• Helps both pro and eukaryotic cells maintain cell shape

• Site of metabolic chemical reactions because it is water based

Cytoskeleton

• Helps maintain the shape of animals cells

• Parts of the cytoskeleton help vesicles get transported around the cell

• 3 parts

  • Actin

  • Microtubules

  • Actin filaments

• Uses:

  • Supports and maintains cell shape

  • Holds organelles in position

  • Moves organelles

  • Involved in cytoplasmic streaming(actin)

    • Movement of cytosol in plants, fungi within the cell

    • Interacts with extracellular structures to anchor cell in place

• Microtubules are made from dimers of the protein tubulin-chains of dimers surround a hollow core

  • They have (+) and (-) ends and show dynamic instability

  • Polymerization results in a rigid structure; depolymerization leads to its collapse

• Microfilaments help a cell or parts of a cell to move

  • Determine cell shape

  • Made from actin monomers that attach to the “plus end” and detach at the “minus end” of the filament

• Dynein is the motor protein that moves cargo in the opposite direction 

Centrioles

• Centrioles make spindle fibers during mitosis and meiosis

• Spindle fibers help pull chromosomes apart during mitosis and meiosis

• Fun Fact: Centrioles form the flagellar tail of sperm cells

Flagella and Cilia

• Both flagella and cilia help move cells around

• Flagella are longer and move like a propeller

• Cilia are much shorter and move in a back and forth-beating motion

• Structures for cell motility

• 9+2 internal structure

• Membrane Bound Organelles

  • Nucleus

  • Nucleolus

  • Smooth ER

  • Rough ER

  • Golgi Apparatus

  • Lysosome

  • Peroxisome

  • Vacuole

  • Mitochondrion

  • Chloroplast

• Nucleus

  • Surrounded by a double nuclear membrane that houses and protects DNA from denaturation

  • Also the site of transcription, the process in which DNA is transcribed into mRNA

• Nucleolus

  • Also responsible synthesis of ribosomal RNA(rRNA)

  • Site of ribosome synthesis in the cell

• Smooth ER

  • Responsible for lipid/hormone synthesis and detoxification of cell wastes

  • Synthesis lipid polymers and hormones get sent to the golgi apparatus

    

• Rough ER

  • Highly folded organelle that is contiguous with the nucleus and has ribosomes attached

  • Responsible for packaging proteins and sending them to the golgi apparatus

    

• Golgi apparatus

  • Similar to a post office for the cell

  • Responsible for:

    • Helping fold and modify proteins

    • Packaging proteins/lipids into vesicles

    • Sending these vesicles to their intended intra or extracellular destination

  • 

• Protein Secretion from the Cell

  • Acronym to remember the pathway: REGVC

    • R-Ribosomes on the rough endoplasmic reticulum synthesize proteins 

    • E-Rough ER

    • G-Golgi Apparatus

    • V-Vesicles

    • C-Vesicles fuse with the cell membrane and allow for secretion of the protein into the extracellular space

    • Acronym to remember the pathway: REGVC (REGular Video Chat)

      R- Ribosomes on the rough endoplasmic reticulum synthesize proteins and import them into the

      E- Rough Endoplasmic reticulum helps fold the proteins and tags them for shipment to the golgi apparatus

      G- Golgi Apparatus packages proteins into vesicles

      V- Vesicles are transported to the cell membrane

      C- Vesicles fuse with the cell membrane and allow for secretion of the protein into the extracellular space.

      

• Peroxisomes

  • Responsible for hydrolysis and also using catalase(an enzyme) to break down hydrogen peroxide(toxic to the cell)

  • Lipids are broken down into fatty acid monomers, which are sent to the mitochondrion to help generate ATP

  • 

• Lysosomes

  • Lipid bubble full of hydrolytic enzymes that break down cell waste and denatures proteins into their monomers

  • Lysosomes are also involved in apoptosis(programmed cell death)

    • Apoptosis

      • Auto-destruct process

      • Ex: Tadpole tail gets reabsorbed where it turns into a frog

      • Ex: Loss of webbing between your fingers between your fingers during fetal development

      • 

• Vacuoles

  • Responsible for storing and releasing fluids/biomolecules

    • Also store cellular waste products until they can be broken down

  • Vacuoles in plants are very, very large and help maintain plant cell shape/turgor pressure

    • Storage of water

    • Vacuoles in animals are usually very small

  • Vacuoles in plants/protists

    • Central vacuoles-storage of waste products and toxic compounds-water

    • Other purposes

      • Reproduction: Vacuoles in flowers and fruits contain pigments who colors attract pollinators and aid seed dispersal

      • Catabolism: Digestive enzymes in seeds’ vacuoles hydrolyze stored food for early growth

      • Contractile vacuoles: In freshwater protists get rid of excess water entering the cell due to solute imbalance

        

• Mitochondria

  • Has two membranes, which allows for compartmentalization of different chemical reactions

    • Outer mitochondrial membrane

      • Smooth, not folded

    • Inner mitochondrial membrane

      • Folding of inner membrane increases surface area to allow for faster/more ATP production

    • Responsible for some of the processes that synthesize ATP

      • Citric Acid Cycle(In the matrix)

      • Oxidative Phosphorylation(on the inner membrane)

      • 

• Chloroplasts

  • Has two membranes, which allows for compartmentalization of different chemical reactions

  • Interna; anatomy is arranged in stack of thylakoid membranes called grana

  • Multiple thylakoids increases surface area so more reactions can occur

  • 

• Extracellular features of cells

  • Animal cells:

    • Cell matrix

      • Hold cells together in tissues

      • Contribute to physical properties of cartilage, skin, and other tissues

      • Filter materials

      • Orient cell movement during growth and repair

    • Cell Junctions

      • Specialized structures that protrude from adjacent cells and “glue” them together

        • Tight junctions-cells meet edge to edge and seal together

        • Desmosomes-Attach two cells to each other but do so in a way that allows extracellular fluid can still move between them

        • Gap junctions-Big channel proteins that go through two cells

        • Plant cells have tiny holes called plasmodesmata which are channels that allows the movement of water, ions, small molecules, hormones, and some RNA and proteins

        • Adjacent plant cells are connected by plasma membrane-lined channels called plasmodesmata.

          These channels allow movement of water, ions, small molecules, hormones, and some RNA and proteins.

          
          

          

• The plant cell wall has three major roles:

  • Provides support for the cell and limits volume by remaining rigid

  • Acts as a barrier to infection

  • Contributes to form during growth and development

Structure and function of the Cell Membrane

• Overview of the Plasma Membrane

  • The plasma membrane is composed of a phospholipid bilayer with embedded proteins and cholesterol molecules

  • The fluid-mosaic model of the plasma membrane describes the fluidity of the membrane and its components. Phospholipids are embedded proteins that move freely around one another, forming a “fluid mosaic”. 

  • Functions of the plasma membrane

    • Separates the internal cytoplasm from the external environment of the cell

    • Controls the movement of substances in and out of the cell

    • Allows cells to communicate with one another and interact with their external; environment

• Plasma membrane Components

  • Lipid component referred to as the phospholipid bilayer

    • The hydrophilic polar heads of the phospholipid molecules line the internal(cytoplasmic) and external(extracellular) surface of the membrane

    • The hydrophobic fatty-acid tails of the phospholipids are sandwiched between 

  • Protein Molecules: Float around like icebergs in a sea of phospholipids

    • Membrane proteins may be peripheral or integral

    • Peripheral proteins are found on the inner membrane surface

      • Found attached to the inside or outside surface of the cell membrane

      • Usually used for cell signaling

    • Integral proteins are partially of wholly embedded(transmembrane) in the membrane

      • Integral proteins are amphipathic, meaning they have both hydrophobic and hydrophilic regions

      • The portion of the protein embedded within the phospholipid is hydrophobic while the portion of the protein exposed to the interior or exterior of the cell is hydrophilic

      • Either fully or partially embedded in the membrane

      • Used for cell signaling

    • Transmembrane Proteins

      • Go all the way through the membrane

      • Usually found as channel proteins that move polar/large molecules in and out of the cell

      • Special type of Integral Protein

  • Cholesterol molecules embedded in the phospholipid bilayer controls the fluidity of the membrane(makes the membrane more or less fluid depending on the temperature)

  • Carbohydrate chains contribute to cell’s “fingerprint”: allow cells to recognize one another

    • Glycoproteins: proteins with attached carbohydrate chains

    • Glycolipids: Phospholipids with attached carbohydrate chains

    • The golgi affs on the chains after the proteins and lipids are produced by the ER

    • Carbohydrates on the external side of the plasma membrane vary among species, individuals, and even cell types in an individual

• Head of phospholipid

  • Contains phosphate, choline, and glycerol

  • Polar

  • Hydrophilic

  • Interacts with water

• Fatty Acid Tails

  • Contains a saturated and unsaturated fatty acid

    • Unsaturated FA is bent which prevents phospholipids from packing too tightly together and allows for membrane fluidity

  • Non-Polar

  • Hydrophobic

  • Avoids water

• Membrane structure

  • What do you think happens when you put a bunch of phospholipids in a water based solution

    • It is energetically unfavorable for the hydrophobic tails to be exposed to water

    • This drives the formation of the phospholipid bilayer(cell membrane)

      • Hydrophilic head groups face aqueous cell interior and exterior

      • Hydrophobic tails form the dense hydrophobic core of the membrane

• Cholesterol

  • Regulates membrane fluidity in response to temperature changes

• Glycolipids

  • Carbohydrate attached to a phospholipid

    • Glycolipids facilitate cell-to-cell adhesion and recognition

  • Glycoproteins

    • Carbohydrate attached to a protein

      • Allow cross linking of cells which gives the tissue strength\

• Fluid Mosaic Model

  • The membrane is frequently referred to as a fluid mosaic. This means it is made of many components that can move laterally in the membrane

• Types of Membrane Proteins

  • Channel Proteins: Allow passage of specific molecules or ions through membrane via a channel protein

    • Transmembrane proteins with a channel through the middle

    • Used for transport of large, polar, or charged molecules across the membrane

  • Carrier Proteins: Combine with the molecule or ion to be transported and assists its passage through membrane

  • Cell recognition proteins(i.e. glycoproteins): Help cells identify one another

  • Receptor Proteins: Shaped in such a way that specific molecules bind to it

    • Allow a cell to respond to signals from other cells

    • Used for cell signaling. Ligands bind to the receptor and cause the cell to respond accordingly

    • Transmembrane or peripheral proteins that do not have a channel through the middle

  • Enzymatic proteins: Catalyze specific reactions

  • Junction proteins: Attach adjacent cells so that a tissue cam fulfill a function

• Permeability of the plasma membrane

  • A cell must regulate transport of substances into and out of the cell

  • The plasma membrane is selectively permeable

    • Allows some substances to move across the membrane

    • Inhibits passage of other molecules, such as polar molecules

    • The membrane only lets small, non-polar molecules diffuse freely through the spaces between the phospholipids

      • Oxygen, carbon dioxide, and water

    • Why?

      • It is energetically favorable for large, charged, polar molecules to interact with the hydrophobic fatty acid tails at the core of the membrane

  • Small, hydrophobic(nonpolar) molecules(such as CO2, O2, and glycerol) freely cross the membrane by passing through the phospholipid bilayer

  • Polar or charged substances, such as sugars and ions do not cross the membrane easily, and rely on transport proteins to cross(such as channel and carrier proteins

• Cell size

  • Cells need a large surface area to adequately exchange materials with their surroundings, and a small volume for materials to quickly travel within the cell

  • The surface-area-to-volume ratio of a cell requires that cells be small

    • Large cells have a small surface area to volume ratio, which decreases the efficiency of transporting materials in and out of the cell

    • Small cells have a large surface-area-to-volume ratio is advantageous for exchanging molecules

• Concentration Gradients

  • A concentration gradient is formed when the concentration of a particle is higher in one area than in another

    • A particle moving from an area of high concentration to an area of low concentration

    • A particle moving against(or up) its concentration gradient is moving from an area of low concentration to an area of high concentration

  • Molarity(mol/L) and osmolarity(#particles/L) are two ways to measure the solute concentration in a solution

• Passive transport

  • Passive transport is the movement of substances across the cell membrane without the input of energy

  • Involves substances moving down their concentration gradient(from high to low concentration)

  • Three types: Osmosis, Diffusion, and facilitated transport

• Diffusion

  • Diffusion is the net movement of molecules down a concentration gradient

  • Molecules move both ways along the gradient, but net movement is from high to low concentration

  • NET movement stops when the molecules reach dynamic equilibrium:

    • Molecules still move both ways, but at equal rates

    • Solute concentration is uniform-no concentration gradient

• Osmosis

  • Osmosis is the diffusion of water across a selectively permeable membrane

  • Water can diffuse both ways across a cell membrane, but some solutes cannot

  • Osmosis occurs when there is a concentration gradient created by a solute that cannot diffuse across the membrane

  • Net movement of water is towards the side with low water concentration(Higher solute concentration)

  • There will be a net movement of water until the two solutions reach dynamic equilibrium

    • Occurs when the two solutions reach the same concentration

    • After that, water will be diffusing in both directions at equal rates

  • Water is small enough to travel directly through the phospholipid bilayer, but many cells have aquaporins, which are integral membrane proteins that water molecules can more easily travel through

    • Aquaporins allow water to travel more rapidly into and out of the cell than by just diffusing through the phospholipid bilayer

• Osmosis: Ionic Solutions

  • A cell can be on of three types of solutions(environments):

    • Isotonic, hypotonic, or hypertonic

  • Isotonic solutions: Solute and water concentrations are equal

    • There is no net gain or loss of water by the cell

• Osmosis:Hypotonic Solutions

  • Hypotonic Solutions: Concentrations of solute in the solution is lower than inside the cell

    • Causes net movement of water into the cell

  • Cells placed in a hypotonic solution will swell

    • Causes turgor pressure in plants, in which the large central vacuole fills with water and pushes against the cell wall=good for plant cells!

    • May cause animal cells to lyse(rupture)=bad for animal cells!

• Osmosis:Hypertonic Solutions

  • Hypertonic Solutions: Concentration of solute is higher in the solution than inside the cell.

    • Causes net movement of water out of the cell

  • Cells placed in hypertonic solution will shrink, which typically causes them to die

  • In plant cells, the cell membrane shrinks, while the rigid cell wall retains its shape

    • This is called plasmolysis, causing the plant to wilt and die

• Facilitated Transport

  • Facilitated transport utilizes membrane proteins to allow for the movement of substances that cannot pass directly through the phospholipid bilayer. 

    • This includes all charged particles(ions) and larger polar molecules

  • Follows concentration gradient, moving from high concentration to low concentration. No energy is required

  • There are two main types of membranes proteins that perform facilitated diffusion: channel proteins and carrier proteins

  • Channels Proteins: Allow specific molecules or ions to quickly tunnel through the cell membrane. Most have hydrophilic passageways

    • EX: Aquaporins and ion channel

  • Carrier proteins: Specific solutes bind to the protein, changing the protein’s shape, which results in the release of the solute on the other side of the membrane

    • EX: glucose and amino acids are molecules that must combine with specific carrier proteins to move across the membrane

Cell Transport

• Importance of Cell Transport

  • Required to maintain homeostasis in the cell

    • Transport of waste out of the cell

      • Helps maintain pH and salt balance

    • Transport signal proteins out of the cell

      • Helps cells communicate, like in the nervous system

    • Absorption of nutrients into the cell

    • Allow oxygen into the cell for respiration

    • Allows for CO2 to leave cells

    • Can assist in apoptosis in infected cells

    • ETC. 

• Concentration Gradient

  • The difference in concentration of molecules across a space

    • One area will have a higher concentration of molecules than the other

  • Biological Concentration gradients occur when there is a difference in the concentration of biomolecules, water or ions across the cell membrane

• Best way to describe on FRQ

  • Molecules moving with the concentration gradient are moving from an area of high concentration to an area of low concentration of the molecule that is moving

• Molecular Energy and Net Movement

  • Atoms/molecules have inherent energy that causes them to vibrate and move around

  • The direction in which the molecules move is random

  • Net movement refers to the overall direction that MOST of the molecules move

  • Net movement of molecules will generally follow the concentration gradient

• Dynamic equilibrium

  • Occurs when molecules moving with the concentration gradient reach the same net concentration on both sides of the membrane

    • Molecules are still moving but the net movement is zero

    • Cells will remain in dynamic equilibrium unless work(using ATP energy) is done to reset the concentration gradient

• Cell Transport

  • Process by which cells exchange nutrients, waste and other materials with the extracellular environment

  • Two types

    • Passive Transport

    • Active Transport

  • Passive Transport

    • Net movement of molecules with the concentration gradient until the system reaches dynamic equilibrium

    • Relies on the inherent energy of the concentration gradient. Does not require the input of metabolic energy(ATP) to occur

    • Three processes

      • Simple diffusion

      • Facilitated diffusion

      • Osmosis

  • Active Transport

    • Net movement of molecules against the concentration gradient. System will not reach dynamic equilibrium

    • Requires a net input of metabolic energy(hydrolysis of ATP) to occur

  • Simple Diffusion

    • Net movement is small. Non-polar molecules with the concentration gradient without the aid of a channel protein

    • Only occurs with: O2, N2, CO2, and small amounts of water

  • Facilitated diffusion

    • Net movement of molecules with the concentration gradient that requires the use of a channel protein to occur

    • Occurs for any molecules that are large, polar, charged or some combination thereof

  • Facilitates Transport

    • Large, polar, and charged molecules require the facilitation(help) of channel proteins to cross the dense hydrophobic core of the membrane

    • Facilitated diffusion and active transport are both examples of facilitated transport

      • Aquaporins(Facilitated Diffusion)

        • Large quantities of water require the help of a special membrane protein called an aquaporins to cross the cell membrane because water is very polar and hydrophilic. Small quantities of water can still osmose though

      • Sodium-Potassium Pump(Active Transport)

        • Responsible for maintaining the concentration gradients of Na+ and K+ ions across the membranes of neurons. This allows for maintenance of membrane potential, which is required for electrochemical signaling in neurons

• Membrane Potential:  A Consequence of Ion Transport

  • Separation of charge across the membrane creates what we call the membrane potential

  • Essentially the membrane is acting like a battery and storing electrical potential energy

  • When ions change concentrations on both sides of the membrane through transport, the membrane can become polarized and fire an electrical signal

• Endocytosis

  • Process by which cells take in molecules into the intracellular space

  • Requires formation of a vesicle for bulk import of substances

• Exocytosis

  • Process by which cells release molecules into the extracellular space

  • Requires formation of a vesicle for bulk export of substances

• Cell Size

  • Cells can be anywhere from 10 micrometers to 1 mm in range

    • Cells have to be big enough to fit all the DNA and organelles, but also have to be small enough to efficiently exchange nutrients, oxygen and waste with the extracellular environment to maintain homeostasis

• Surface Area to Volume Ratio

  • Cells need to have a large surface area to volume ratio to be efficient at transport

  • High surface area = more places for materials to enter/exit. Small volume = less space to cross for materials to get where they need to be

• Projections

  • Having projections(like villi) on a cell will increase the surface area to volume ratio

  • Cells with projections will be more efficient at transporting materials compared to other cell shapes

• Factors That Affect Cell Transport

  • You will be required to calculated

    • Surface area if a shape

    • Volume of a shape

    • Surface Area: Volume Ratio