Unit 2: Cell Structure and Function This document contains all the Essential Knowledge and Terminology student’s are expected to learn. It can be use

  1. Subcellular Components

  • Ribosomes comprise ribosomal RNA (rRNA) and protein. 

  • Ribosomes synthesize protein according to mRNA sequence. 

  • Ribosomes are found in all forms of life, reflecting the common ancestry of all known life.

  • The endomembrane system consists of agroupofmembrane-boundorganelles and subcellular components (endoplasmic reticulum (ER), Golgi complex, lysosomes, vacuoles and transport vesicles, the nuclear envelope, and the plasma membrane) that work together to modify, package, and transport polysaccharides, lipids and proteins intracellularly. 

  • Endoplasmic reticulum provides mechanical support by helping cells maintain shape and plays a role in intracellular transport. 

    • a. RoughER is associated with membrane bound ribosomes, allows for the compartmentalization of cells, and helps carry out protein synthesis. 

    • b. Smooth ER functions include the detoxification of cells and lipid synthesis.

  • The Golgi complex is a membrane-bound structure that consists of a series of flattened membrane sacs— 

    • a. Functions of the Golgi include the correct folding and chemical modification of newly synthesized proteins

    • B. Packaging proteins for trafficking

  • Mitochondria have a double membrane that provides compartments for different metabolic reactions involved in aerobic cellular respiration. The outer membrane is smooth, while the inner membrane is highly convoluted, forming folds that enable ATP to be synthesized more efficiently.

  • Lysosomes are membrane-enclosed sacs that contain hydrolytic enzymes that digest material. Lysosomes also play a role in programmed cell death (apoptosis).

  • A vacuole is a membrane-bound sac that plays many and differing roles. 

    • In plant cells, a specialized large vacuole maintains turgor pressure through nutrient and water storage. 

    •  In animal cells, vacuoles are smaller in size, are more plentiful than in plant cells, and store cellular materials.

  • Chloroplasts are specialized organelles that are found in plants and photosynthetic algae. Chloroplasts contain a double membrane and serve as the location for photosynthesis.




  1. Cell Size

  • Surface area-to-volume ratios affect the ability of a biological system to obtain necessary resources, eliminate waste products, acquire or dissipate thermal energy, and otherwise exchange chemicals and energy with the environment. 

RELEVANT EQUATIONS 

Volume of a Sphere: r 4 V = π 3 3 

Volume of a Cube: V = s2 

Volume of a Rectangular Solid: V = lwh 

Volume of a Cylinder: V = πr h2 

Surface Area of a Sphere: SA = 4pr 2 

Surface Area of a Cube: SA s = 6 2 

Surface Area of a Rectangular Solid: SA = 2lh + 2lw + 2wh 

Surface Area of a Cylinder: SA = 2πrh + 2πr2 

r = radius l = length h = height w = width s = length of one side of a cube



  • The surface area of the plasma membrane must be large enough to adequately exchange materials. 

    • The surface area-to-volume ratio can restrict cell size and shape. Smaller cells typically have a higher surface area-to-volume ratio as well as a more efficient exchange of materials with the environment than do larger cells. 

    • As cells increase in volume, the surface area-to-volume ratio decreases and the demand for internal resources increases. 

    • More complex cellular structures (e.g., membrane folds) are necessary to adequately exchange materials with the environment.

    • As organisms increase in size,their surface area-to-volume ratio decreases, affecting properties like rate of heat exchange with the environment. Smaller amounts of mass exchange proportionally more heat with the ambient environment than do larger masses. As mass increases, both the surface area to-volume ratio and the rate of heat exchange decrease. 

    • There is a relationship between metabolic rate per unit body mass and the size of multicellular organisms; typically, the smaller the organism, the higher the metabolic rate per unit body mass.



  1. Plasma membranes

  • Phospholipids have both hydrophilic and hydrophobic regions. 

  • The hydrophilic phosphate regions of the phospholipids are oriented toward the aqueous external or internal environments, while the hydrophobic fatty acid regions face each other within the interior of the membrane. 

  • Embedded proteins can be hydrophilic (with charged and polar side groups), hydrophobic (with nonpolar side groups), or both. 

    • Hydrophilic regions of the proteins are either inside the interior of the protein or exposed to the cytosol (cytoplasm). 

    • Hydrophobic regions of proteins make up the protein surface that interacts with the fatty acids in the interior membrane.

  • Plasma membranes consist of a structural framework of phospholipid molecules embedded with proteins, steroids (such as cholesterol in vertebrate animals), glycoproteins, and glycolipids. All of these can move around the surface of the cell within the membrane, as illustrated by the fluid mosaic model.



  1. Membrane Permeability

  • The structure of cell membranes results in selective permeability. 

  • Cell membranes separate the internal environment of the cell from the external environment. 

  • Selective permeability is the result of the plasma membrane having a hydrophobic interior.

  • Small nonpolar molecules, including N2, O2, and CO2 , freely pass across the membrane. Hydrophilic substances, such as large polar molecules and ions, move across the membrane through embedded channels and transport proteins.

  • The nonpolar hydrocarbon tails of phospholipids prevent the movement of ions and polar molecules across the membrane. Small polar, uncharged molecules, like H2O  or NH3 (ammonia), pass through the membrane in small amounts.

  • Cell walls of Bacteria, Archaea, Fungi, and plants provide a structural boundary as well as a permeability barrier for some substances to the internal or external cellular environments and protection from osmotic lysis.

  • Cell walls of plants, prokaryotes, and fungi are composed of complex carbohydrates.



  1. Membrane Transport

  • Passive transport is the net movement of molecules from high concentration to low concentration without the direct input of metabolic energy. 

  • Passive transport plays a primary role in the import of materials and the export of wastes. 

  • Active transport requires the direct input of energy to move molecules from regions of low concentration to regions of high concentration.

  • The selective permeability of membranes allows for the formation of concentration gradients of solutes across the membrane. 

  • The processes of endocytosis and exocytosis require energy to move large substances or large amounts of substances into and out of cells. 

    • In endocytosis, the cell 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. 

    •  In exocytosis, internal vesicles release material from the external environment.



  1. Facilitated Diffusion

  • Membrane proteins are required for facilitated diffusion of charged and large polar molecules through a membrane— 

    • a. Large quantities of water pass through aquaporins. 

    • b. Charged ions, including Na+ and K+, require channel proteins to move through the membrane. 

    • c. Membranes may become polarized by movement of ions across a membrane.

  • Facilitated diffusion enables the movement of large polar molecules through membranes with no energy input. In this type of diffusion, substances move down the concentration gradient. 

  • Aquaporins transport large quantities of water across membranes.



  1. Tonicity and Osmoregulation

  • External environments can be hypotonic, hypertonic or isotonic to internal environments of cells— 

    • a. Water moves by osmosis from areas of high water potential/low osmolarity/ low solute concentration to areas of low water potential/high osmolarity/high solute concentration.

 RELEVANT EQUATION 

Water Potential: Ψ = Ψs + Ψp 

Ψp = pressure potential 

Ψs = solute potential

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

  • Osmoregulation maintains water balance and allows organisms to control their internal solute composition and water potential. Water moves from regions of low osmolarity or solute concentration to regions of high osmolarity or solute concentration.



  • SOLUTE POTENTIAL OF A SOLUTION 

Ψs = −iCRT 

where: i = ionization constant C = molar concentration

 R = pressure constant R = 0.0831 

T = temperature in Kelvin (°C + 273)



  1. Mechanisms of Transport

  • Metabolic energy (such as that from ATP) is required for active transport of molecules and ions across the membrane and to establish and maintain electrochemical gradients. 

    • Membrane proteins are necessary for active transport. 

    • The Na+ + /K pump and ATPase contribute to the maintenance of the membrane potential.



  1. Compartmentalization

  • Membranes and membrane-bound organelles in eukaryotic cells compartmentalize intracellular metabolic processes and specific enzymatic reactions. 

  • Internal membranes facilitate cellular processes by minimizing competing interactions and by increasing surface areas where reactions can occur.



  1. Origins of Cell Compartmentalization

  • Membrane-bound organelles evolved from once free-living prokaryotic cells via endosymbiosis. 

  • Prokaryotes generally lack internal membrane bound organelles but have internal regions with specialized structures and functions. 

  • Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.



Terminology 



  • Surface Area to Volume Ratio

  • Compartmentalization

  • Solute

  • Cytosol

  • Eukaryotic cell

  • Prokaryotic cell

  • Nucleoid

  • Cytoplasm

  • Plasma membrane

  • Nuclear envelope

  • Chromosomes

  • Nucleolus

  • Ribosomes

  • Endomembrane system

  • Vesicles

  • Endoplasmic reticulum

  • Smooth er

  • Rough er

  • Transport vesicles

  • Lysosome

  • Vacuoles

  • Food vacuoles

  • Contractile vacuoles

  • Mitochondria

  • Chloroplasts

  • Plastids

  • Peroxisome

  • Cytoskeleton

  • Motor protein

  • Microtubules

  • Centrosome

  • Centrioles

  • Flagella

  • Cilia

  • Microfilaments

  • Cell wall

  • Plasmodesmata

  • Gap junctions

  • Tight junctions

  • Amphipathic

  • Fluid mosaic model

  • Integral proteins

  • Transmembrane proteins

  • Peripheral Proteins

  • Glycolipids

  • Glycoproteins

  • Selective permeability

  • Transport protein

  • Channel Proteins

  • Carrier Proteins

  • Aquaporins

  • Concentration gradient

  • Passive transport

  • Osmosis

  • Isotonic

  • Hypertonic

  • Hypotonic

  • Osmoregulation

  • Turgid

  • Flaccid

  • Plasmolysis

  • Facilitated diffusion

  • Ion channels

  • Gated channels

  • Active transport

  • Sodium potassium pump

  • Proton pump

  • Endocytosis

  • Phagocytosis

  • Receptor Mediated Endocytosis

  • Exocytosis

  • Tonicity