Introduction to Cells Quiz

Introduction to Cells

• Cells are the basic, living, structural, and functional units of the body
• Cell biology is the study of cellular structure and function
• Cells perform chemical reactions called metabolism to create life processes

A Generalized Cell

• Plasma membrane: Encloses the cell, the outer boundary; separates the cell's internal environment (living) from the external environment (non-living).
  • It's a bilayer of phospholipids, a selective barrier
  • Plays a role in cellular communication
• Cytoplasm: Fills the interior of the cell, a semi-fluid substance
  • Contains macromolecules essential for cellular activity
  • Contains organelles
  • Cytosol: Part of the cytoplasm that contains water, organic molecules, and ions.
  • Cytoplasm is the collective term for cytosol plus organelles
• Nucleus: Centrally located organelle; contains chromosomes.
  • Consists of a single molecule of DNA and associated proteins
  • Each chromosome contains thousands of hereditary units called genes

A Generalized Cell (continued)(Figure)

• Organelles
• Cytoskeleton
• Microtubules
• Microfilaments
• Intermediate filaments
• Microvilli
• Centrosome (pericentriolar material and centrioles)
• Lysosomes
• Smooth endoplasmic reticulum
• Peroxisomes
• Mitochondria
• Ribosomes
• Golgi Complex
• Vacuoles
• Nucleolus
• Chromatin

The Plasma Membrane

• Integral proteins: Extend through the lipid bilayer
• Peripheral proteins: Attached to the inner or outer surface of the membrane, do not extend through it.
• Some integral proteins are ion channels
• Transporters: Selectively move substances through the membrane
• Receptors: For cellular recognition; a ligand is a molecule that binds with a receptor
• Enzymes: Catalyze chemical reactions
• Others act as cell-identity markers

The Plasma Membrane (continued)(Figure)

• Phospholipids: Polar head (hydrophilic), fatty acid tails (hydrophobic) - Bilayer
• Cholesterol: In the lipid bilayer
• Glycolipids: Carbohydrate + Lipid
• Glycoproteins: Carbohydrate + Protein

The Plasma Membrane

• Selectively permeable
  • Allows oxygen, carbon dioxide, water, and steroids to pass through
  • Does not allow glucose, proteins, and ions to pass through directly
• How do materials enter the cell?
  • Integral proteins act as channels
  • Na+/K+ pump, G protein, Tyrosine Kinase Pathway
• Intracellular fluid (ICF): Fluid within the cells (also called cytosol)
• Extracellular fluid (ECF): Fluid outside cells
  • Interstitial fluid: ECF filling the spaces between cells
  • Plasma: ECF in blood vessels
  • Lymph: ECF in lymphatic vessels

Membrane Transport

• Passive transport: High to low concentration (with concentration gradient); no ATP needed
• Active transport: Low to high concentration (against concentration gradient); ATP needed
• Diffusion: Net movement of a substance from a region of high concentration to a region of lower concentration
• Osmosis: Net movement of water through a selectively permeable membrane from an area of high concentration to a lower concentration
• Facilitated diffusion: Net movement of a substance through an integral protein from a region of high concentration to a region of lower concentration
• Na+/K+ pump: Transports ions across the plasma membrane (antiporter); requires ATP; moves from lower to higher concentration

Membrane Transport(continued)

• Vesicle: A small spherical sac formed by budding off from the Golgi apparatus membrane, plasma membrane or lysosome membrane.
• Exocytosis: Vesicles fuse with the plasma membrane, releasing their contents into the extracellular fluid (ECF)
• Endocytosis: Materials move into a cell in a vesicle; includes receptor-mediated endocytosis, phagocytosis, and pinocytosis

Cytoplasm

• Ribosomes: Site of protein synthesis(Figure)
  • Composed of rRNA and proteins
  • Attach to internal membranes of the endomembrane system
  • Float freely in the cytoplasm; Composed of 2 subunits

Cytoplasm (continued)

• Endomembrane system: Endoplasmic Reticulum (ER), Golgi Apparatus, Lysosomes, Microbodies (Peroxisome), Vacuoles

Cytoplasm (continued)(ER)

• Endoplasmic Reticulum (ER): Membrane-bound; embedded proteins
  • Cisternal space (lumen)
  • Two types:
    • Smooth ER
    • Rough ER
  • Rough ER contains embedded ribosomal proteins
  • Smooth ER contains enzymes that catalyze the synthesis of carbohydrates and lipids, stores ions and steroids

Cytoplasm (continued)

• Golgi apparatus: Collects, sorts, packages, and distributes proteins and other substances
  • Modifies proteins and lipids from the ER
  • Creates glycolipids or glycoproteins (addition of short sugar chains)
  • Abundant in glandular cells; secretion is high
  • Cis face: Receiving end, near ER
  • Trans face: Distribution end, faces plasma membrane. Products packaged into vesicles at the trans face.

Cytoplasm (continued)(Lysosomes)

• Lysosomes: Digestive vesicles
  • Arise from the Golgi apparatus (trans face)
  • Contain hydrolytic enzymes
  • Function in phagocytosis (of macromolecules, particles, and worn-out organelles)

Cytoplasm(continued)(Microbodies)

• Peroxisomes: Contain digestive enzymes
  • Produce hydrogen peroxide as a byproduct
  • Contain detoxifying enzymes
  • Break down hydrogen peroxide into water and oxygen.
  • Isolate oxidative enzymes to decrease disruptions to metabolic reactions in the cytoplasm

Cytoplasm(continued)(Vacuoles)

• Vacuoles: Storage depots for water, sugars, ions, and waste products.

Cytoplasm (continued)

• Centrioles: Microtubule organizing centers
  • Occur in pairs
  • Move to opposite poles of the cell during cell division
  • Cylindrical in shape; composed of 9 triplet rows of microtubules

Cytoplasm (continued)(Mitochondria)

• Mitochondria: Contain their own DNA
  • Proteins (essential for function) are produced via these genes.
  • Can duplicate themselves during cell replication
  • Contain oxidative enzymes for transferring energy from macromolecules to ATP.
  • Surrounded by two membranes (outer and inner membranes)
  • Inner membrane has cristae (increases surface area).
  • Matrix is the "cytoplasm" of the mitochondrion

Cytoplasm (continued)(Cytoskeleton)

• Cytoskeleton: Network of protein fibers
• Supports the shape of the eukaryotic cell
  • Keeps organelles in fixed locations
  • Helps move materials within the cell
• Types:
  • Microtubules
  • Actin filaments (muscle contraction)
  • Intermediate filaments (structural stability), e.g. keratin, neurofilaments

Cytoplasm (continued)(Cilia and Flagella)

• Cilia: Short, hair-like projections from the cell surface; move fluids along the cell surface.
• Flagella: Longer than cilia; move the entire cell.

Nucleus (continued)

• Nucleus: Largest organelle (usually one per cell)
  • Centrally located
  • Stores genetic information
  • Contains nucleolus (involved in rRNA synthesis)

Nucleus (continued) (Nuclear Structure and Function)

• Surrounded by the nuclear envelope
  • Outer and inner membrane
• Pores in the envelope
  • Allow proteins into the nucleus
  • Allow RNA and RNA-protein complexes out of the nucleus to cytoplasm.

Interphase

• Interphase is divided into three phases:
  • G1: Gap Phase 1 (cell growth)
  • S: Synthesis phase (DNA replication)
  • G2: Gap Phase 2 (chromosomes condense; protein synthesis)

Mitosis

• Mitosis is divided into five phases
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase

Cellular Diversity

• Average adult has nearly 100 trillion cells
• About 200 different types of cells
• Cells vary in shapes and sizes
• Cellular diversity allows organization into tissues and organs