Stanbridge - T1 - Physiology - W2 - Cellular Transport, Membrane, Metabolism, Tissue and Tissue Types

Cellular Transport and the Cell Membrane

• Cellular transport is the movement of substances across the cell membrane
• The cell membrane is selectively permeable, allowing some substances to pass through easily while preventing others
• Two main types of transport: passive and active
• Passive transport doesn't require energy; substances move down their concentration gradient
• Active transport requires energy (ATP) to move substances against their concentration gradient

Lecture Objectives

• Understand cellular transport functions of membrane proteins
• Identify different types of transport across/through the cell membrane
• Comprehend various diffusion, osmosis, and active transport mechanisms
• Explain membrane potential
• Describe and illustrate the cell cycle, specifically mitosis
• Understand the processes of protein synthesis (transcription and translation)

Membrane Proteins Involved with Transport

• Passive transport: Membrane proteins facilitate the movement of substances from high to low concentration
• Hydrophilic channels selective for specific solutes
• Specific examples: water, oxygen, carbon dioxide
• Active transport: Membrane proteins use ATP to actively pump substances across the membrane, often against their concentration gradient
• Examples include Na+/K+ pump

Membrane Proteins Involved in Signal Transduction

• Receptors: Membrane proteins with binding sites shaped to fit specific chemical messengers (e.g., hormones)
• Binding initiates a chain of events within the cell

Membrane Proteins Involved in Catalyzing Reactions

• Enzymatic activity: Membrane proteins can act as enzymes with active sites exposed for reactions in solution.
• Sequential steps in metabolic pathways are catalyzed by different enzymes working together.

Membrane Proteins Involved with Cell Recognition

• Cell-cell recognition: Glycoproteins act as markers, facilitating cell identification

Membrane Proteins Anchor the Inside and Outside of the Cell

• Attachment to the cytoskeleton and extracellular matrix: Membrane proteins are anchored to both, keeping cells in position
• Playing roles in cell movement or binding adjacent cells

Intercellular Joining

• Proteins of adjacent cells connected
• Cell adhesion molecules (CAMs) provide temporary binding sites (migration, interactions)
• Nutrients transferred and structural support facilitated.

Cell Junctions: Tight Junctions

• Series of integral proteins fused between cells, creating an impermeable junction
• Some junctions may exhibit leakiness

Cell Junctions: Desmosomes

• Thin protein filaments connect cells at different points, distributing tension
• Found in tissues subject to stretching (skin, heart)

Cell Junctions: Gap Junctions

• Cylindrical proteins connect cells, facilitating communication
• Permeable properties determined by membrane types
• Location in excitable tissues

Membrane Transport

• Plasma membranes are selectively permeable, allowing some substances to pass easily and others being prevented
• Substances can cross membranes by passive or active transport

Types of Membrane Transport

• Passive transport (no ATP) : Substances move down their concentration gradient
• Active transport (requires ATP): Substances move against their concentration gradient

Concentration Gradient

• Difference in solute/substance concentration across a barrier

Types of Passive Transport

• Diffusion: movement of particles from high to low concentration, achieving uniform mixing
• Simple diffusion: movement of nonpolar substances directly through the phospholipid bilayer
• Osmosis: diffusion of water across a selectively permeable membrane to equalize water concentrations
• Facilitated diffusion: use of membrane proteins (channels or carriers) to speed up the movement of substances along the gradient; important for large or charged molecules

Passive Processes

• Diffusion: particles move from areas of high concentration to low concentration
• Simple diffusion: Some examples of molecules that pass through membrane include water, oxygen, and carbon dioxide
• Non-polar, hydrophobic, lipid-soluble substances can pass directly

Passive Processes (cont.)

• Facilitated diffusion: use of membrane proteins (channels or carriers) to help polar molecules pass across the membrane more easily
• Carrier-mediated: binding sites allow small amounts of substances to pass; cavity not simultaneously open to both environments
• Channel-mediated: Allows multiple substances to pass across membrane at same time

Terms used in Diffusion

• Osmotic concentration: Measure of dissolved particles in solution
• Osmolality: Measure of dissolved particles in a solvent

Diffusion where a membrane is permeable to solutes and water

• At equilibrium, both sides have same osmolarity; volume unchanged

Osmosis

• Water moves across a membrane from lower to higher concentrations to even it out
• A form of simple diffusion

Passive Processes (cont.)

• Osmosis: water diffuses from higher to lower osmotic concentration (dilute substance) to a lower concentration

Importance of Osmosis

• Changes in cell volume cause tissues to swell or shrink
• Uncontrolled changes impact cell function, especially neurons

Osmosis and Tonicity

• Penetrating solutes: diffuse freely across the membrane; "pull" water with them
• Non-penetrating solutes: cannot pass through cell membranes; water must move to balance

Tonicity

• Ability of a solution to change or alter cell shape by altering cell's internal water volume

Isotonic Solution

• Solutions with same solute concentrations as inside the cell; water moves into and out of the cell
• Cell retains normal size and shape

Hypertonic Solution

• Solutions with higher solute concentrations than inside the cell; water moves out of cell
• Cell loses water and shrinks (crenation)

Hypotonic Solution

• Solutions with lower solute concentrations than inside the cell; water moves into cell
• Cell swells and may burst (lysis)

Summary of the types of passive transport across the plasma membrane

• Simple diffusion, carrier facilitated diffusion, channel mediated facilitated diffusion, and osmosis are shown in relation to the phospholipid bilayer.

Membrane Transport: Active Processes

• Two types: Active transport, Vesicular transport
• These require ATP to move substances across plasma membranes because of these factors:
  • Solute size (too large for channels)
  • Solubility in lipids (not lipid soluble)
  • Gradient (moving against)

Active Transport

• Requires a carrier protein, binds substances specifically and reversibly
• Moves solutions against their concentration gradient
• Requires energy (ATP)

Active Transport: Two Types

• Primary active transport: Directly requires energy from ATP
• Secondary active transport: Indirectly uses energy from ionic gradients established by primary active transport

Ions (review)

• Atoms or molecules with electrical charges (positive or negative)
• Cations (positive) examples include Na+ and K+
• Anions (negative) examples include Cl−

Sodium-Potassium Pump

• Channels allow slow leakage down concentration gradients
• Pump works as an antiporter
• Maintains Na+ and K+ gradients
• Located in all plasma membranes
• Pumps 3 Na+ out of the cell while pumping 2 K+ into the cell
• High intracellular K+ and extracellular Na+ concentration

Secondary Active Transport

• Driven by the concentration gradient created by primary active transport
• E.g., Na+ diffuses back across the membrane through a membrane cotransporter protein

Vesicular Transport

• Moving particles in and out of cells through vesicles (sections of membrane pinched off)
• Requires energy (ATP)
• Endocytosis
• Exocytosis

Endocytosis

• Phagocytosis: engulfing large or solid materials
• Pinocytosis: engulfing extracellular fluid and solutes
• Receptor-mediated endocytosis: Specific receptors bind certain substances, facilitating membrane folding for uptake.

Exocytosis

• Usually stimulated by things bound on the cell surface
• Examples of products released: hormones, neurotransmitters, wastes, and mucus

Cell Growth and Reproduction (Focus: Chapter 2)

• DNA is organized into chromosomes (e.g., humans have 46 chromosomes, 23 pairs)

Cell Cycle (Focus: Interphase, Mitosis)

• Interphase, Growth and DNA synthesis, growth and final preparations for division are presented graphically
• Cytokinesis is included.
• Phases of mitosis are listed including interphase(G0, G1, S, G2).

DNA and RNA

• DNA bases: Adenine, Thymine, Cytosine, Guanine
• RNA bases: Adenine, Uracil, Cytosine, Guanine

The Process of Protein Synthesis

• Transcription (in nucleus): mRNA is created from DNA
• mRNA carries genetic code from nucleus to cytoplasm

DNA and Protein Synthesis (Translation)

• Translation (in cytoplasm): Ribosomes translate mRNA into protein

Transcription and Translation

• Process showing how DNA translates into functional proteins

Focus on Translation Details

• Steps of translation(elongation, termination and initiation) are detailed

Cellular Metabolism

• Sum of all biochemical reactions in the body
• Two main parts: Anabolism(build larger molecules from smaller ones) and Catabolism (breaks down larger molecules into smaller ones)

Major Stages of Energy Processing

• GI tract: Digests food. Material is absorbed into the blood and transported to cells.
• In tissues: Anabolic and catabolic reactions in the cytoplasm(example: glycolysis)
• In mitochondria: Primarily catabolic reactions, requiring oxygen to produce water, CO2 and ATP via Kreb's cycle and oxidative phosphorylation.

Cellular Respiration

• Catabolic reactions where food is broken down to produce ATP.
• Stages of cellular respiration (glycolysis, Krebs cycle, oxidative phosphorylation) presented in summary, with ATP production highlighted.
• Body can store energy as glycogen and fat.
• ATP fuels energy releasing catabolic reactions that then perform cellular work

Carbohydrates, Proteins, and Fats in Energy Processing

• Different nutrient pathways are illustrated and summarized as they relate to energy production, focusing on carbohydrates, proteins, and fats

Glycolysis, Krebs/Citric Acid Cycle, Oxidative Phosphorylation

• The steps of these major metabolic pathways are detailed regarding ATP production
• Diagram depicting the energy yield of glucose for oxidative phosphorylation

Electron Transport Chain

• Electron transport chain steps and processes are explained
• Diagrams provided illustrating free energy released during the processes

ATP Synthase

• ATP synthase structure and function are described
• Illustrates how the enzyme harnesses energy from the proton gradient to make ATP.

Total ATP Yield From One Glucose Molecule

• Summary table quantifies the total ATP obtained from the breakdown of one glucose molecule

Tissues and Tissue Types

• Four basic tissue types: Epithelial, Connective, Muscular, and Nervous,
• The functions of these tissues are explained, as are examples of each type.

Epithelial Tissue Naming

• Classification based on the number of cell layers (simple, stratified) and cell shape (squamous, cuboidal, columnar)
• Names of epithelium are shown as a combination of these features.

Epithelial Tissue Structure

• Two surfaces : apical and basal
• Apical surface faces the outside of the body, or an open space
• Basal surface is attached to the underlining connective tissue

Simple Epithelia

• Epithelia with a single layer of cells are for absorption, secretion, filtration, and not very protective

Simple Squamous Epithelium

• Endothelium: Lines blood vessels
• Mesothelium: Lines ventral body cavity

Simple Cuboidal Epithelium

• Function: Secretion and absorption
• Examples: Kidney tubules, small glands, ovary surface

Simple Columnar Epithelium

• Function: Absorption, secretion of enzymes/mucus
• Examples: Most of the GI tract lining and parts of the uterus

Pseudostratified Columnar Epithelium

• Function: Secrete substances (especially mucus)
• Location: ciliated (trachea, respiratory tract), non-ciliated (ducts that carry sperm)

Stratified Squamous Epithelium

• Function: Protects underlying tissue in areas that experience friction
• Examples: Non-keratinized (mouth, esophagus), Keratinized (epidermis)

Transitional Epithelium

• Function: Stretches
• Examples: Ureters, bladder, parts of the urethra

Glands and Glandular Epithelium

• Gland: Cell(s) that make and secrete a product.
• Unicellular exocrine glands between epithelial sheets
• Multicellular exocrine glands develop from invaginations of epithelial sheets
• Most have ducts that connect to epithelial sheets
• Exocrine glands release via bursting (holocrine) or exocytosis (merocrine)
• Endocrine glands do not have ducts; secrete into extracellular space (blood or lymphatic fluid); produce hormones

Connective Tissue: Types and Categories

• Proper, Cartilage, Bone, and Blood are listed

Connective Tissue Functions

• Binding and supporting
• Protecting
• Insulating
• Storing and reserving fuel
• Transporting substances
• The overall tissue contains macrophages, WBCs, mast cells, and fat cells

Connective Tissue Distinct Features

• Varying vascularity
• Primarily composed of non-living extracellular matrix
• Capacity to withstand stress
• Most diverse type of tissue

Components of Connective Tissue

• Ground substance, Fibers, Cells

Ground Substance

• Mostly fluid, acting as a diffusion medium
• Can be fluid or viscous
• Composed of interstitial fluid, proteins, and proteoglycans

Connective Tissue Fibers

• Collagen: High tensile strength (resists pulling forces)
• Elastin: Allows stretch and recoil
• Reticular: Supports other tissue types

Connective Tissue Cells

Cell types:

• Fibroblasts
• Chondrocytes
• Osteoblasts, others
• Immature cells (-blast) and mature cells (-cyte) are discussed
• Examples include stem cells (blood making tissue)/plasma

Schematic of Connective Tissue Types

A tree diagram of connective tissue types

Connective Tissue Proper: Loose Connective Tissue- Areolar

• Function: Surrounds organs; supports and pads
• Role in inflammation and fluid exchange

Connective Tissue Proper: Loose Connective Tissue- Adipose

• Function: Energy storage; insulation padding

Connective Tissue Proper: Loose Connective Tissue- Reticular

• Function: Provides support for cells in lymphoid organs

Connective Tissue Proper: Dense Connective Tissue- Dense Regular

• Function: Tensile strength in one direction; used for attachments

Connective Tissue Proper: Dense Connective Tissue- Dense Irregular

• Function: Strength in many directions; supportive

Connective Tissue Proper: Dense Connective Tissue- Elastic

• Function: Stretches and recoils; used in areas needing flexibility and elasticity

Connective Tissue: Cartilage- Hyaline

• Function: Provides cushioning & support; important for joints

Connective Tissue: Cartilage- Elastic

• Function: Flexible support; important in structures needing flexibility

Connective Tissue: Cartilage- Fibrocartilage

• Function: Strong shock absorption; often found where support and strength are needed (e.g., spinal discs)

Connective Tissue: Bone

• Function: Support, protection, levers for muscles
• Contains minerals, fat, and marrow where blood cells are formed
• Bone is well vascularized

Connective Tissue: Blood

• Function: Transports substances, including gases, nutrients and waste
• Fluid matrix within which blood cells are found
• Contains cellular components like red and white blood cells and platelets

Muscular Tissue

• Very cellular; well-vascularized
• Responsible for most body movement
• Types include Skeletal, Cardiac, and Smooth

Skeletal Muscle Tissue

• Function: Voluntary movements, attaches to bones, sometimes skin
• Contains striated fibers (multinucleated)

Cardiac Muscle Tissue

• Function: Involuntary control, maintains blood flow in body cavities
• Contains striated, branching cells w/ intercalated discs

Smooth Muscle Tissue

• Function: Involuntary control, moves substances through internal body cavities
• No striations; one nucleus per cell

Nervous Tissue

• Function: Cells generate and conduct nerve impulses, supporting cells protect and support neurons
• Long cells are part of the tissues in structures like brain, spinal cord, and nerves

Test your knowledge of key concepts in cell biology, including the functions of glycolysis and oxidative phosphorylation, types of tissues, and energy storage mechanisms. This quiz covers essential material that is foundational to our understanding of cellular processes.