LECTURE NOTES Structures In The Cell

Nucleus

• Control center of the cell

• Largest organelle

• Usually the only organelle visible with a light microscope

Nucleus Structures

• Nuclear envelope

  • Phospholipid bilayer

    • Nuclear pores allow molecules and ions in and out of the nucleus

Nuclear pores allow molecules and ions in and out of the nucleus

• messenger RNA (mRNA)

  • passes out of nucleus

  • involved in protein synthesis

Nucleus Structures

• Nuclear envelope

  • Phospholipid bilayer

    • Nuclear pores allow molecules and ions in and out of the nucleus

Nuclear pores allow molecules and ions in and out of the nucleus

• ribosomes

• enzymes

  • from cytoplasm to the nucleus

• hormones

  • activate certain genes

Nucleus Structures

• Nucleoplasm

  • jelly-like fluid containing

    • nucleolus

      • spherical body made of RNA

The nucleolus produces ribosomes

Nucleus Structures

• Chromatin

  • latent chromosomes

  • made of DNA and protein

Cytoplasm Structures

• Cytosol

  • intracellular fluid - complex, semitransparent mixture

  • 60-80% water plus dissolved solutes

    • soluble proteins

    • salts and sugars

Cytoplasm Structures

• Inclusions - transient chemical substances such as:

stored nutrients

• glycogen

secretory products

• mucus

pigment granules

• melanin

oil droplets

Mitochondria

• Powerhouse of the cell

• Produces readily usable energy in the form of ATP

Ribosomes

• The site where protein synthesis occurs

• Small granules of protein and RNA

Only organelle without a membrane

Ribosomes Locations

• Nucleoli

• Cytosol - intracellular fluid

• The outer surfaces of the rough ER and nuclear envelope

Ribosome Functions

• Interprets coded genetic messages (mRNA) and assembles amino acids into proteins according to the specified by the code

• Unattached ribosomes scattered throughout the cytoplasm make enzymes and other proteins for use within the cell
  
  

• Attach to the rough ER and helps make proteins that are destined to be packed into lysosomes

  • In cases of things like digestive enzymes, these proteins will be secreted from the cell

Endoplasmic Reticulum (ER)

• Branching network of membranes throughout cytoplasm

• Involved in intracellular communication (inside of the cell)

Rough Endoplasmic Reticulum

• Contains ribosomes, causing it to have a rough or grainy appearance

• Involved in protein synthesis

  • Involved especially in the creation of proteins that are to be involved in exocytosis or deployment in lysosomes

Smooth Endoplasmic Reticulum

• Contains NO ribosomes

• Smooth in appearance

• Involved in tasks such as

  • lipid synthesis

  • detoxification

  • calcium storage and release

  • found in liver cells

Golgi complex

• Packages proteins received from the rough ER, which are used inside and outside of the cell for various functions

• Involved in the modification of newly synthesized proteins, lipids, and carbohydrates

• Synthesizes lysosomes and secretory vesicles

Golgi vesicles

• Some break off and become secretory vesicles

• Carry cell products to cell surface for exocytosis

• Some become lysosomes

Vesicles

Membranous sacs or bags containing various substances for intracellular use and/or extracellular secretionL

Lysosome Functions

• Vesicles containing powerful hydrolytic enzymes (enzymes that destroy things with water molecules)

• Help destroy foreign substances entering the cell

• Contains enzymes for intra-cellular digestion

Lysosome Functions

• Involved in autophagy, or the digestion of worn out organelles

• Involved in apoptosis

• Involved in glucose mobilization in the liver, or the degradation of stored glycogen into glucose

Cytoskeleton

• A group of microfilaments, intermediate filaments, and microtubules

• Form an internal scaffolding that suspends organelles and gives shape to the cell

Cytoskeleton - Microfilaments TERMINAL WEB

• Made of the protein actin

• Forms a fibrous mat called the terminal web (membrane skeleton) on the cytoplasmic side of the plasma membrane

• The phospholipid bilayer spreads out and rests on the terminal web which provides the bilayer with physical support

Cytoskeleton - Intermediate Filaments

• Thicker and stiffer than microfilaments

• Gives the cell its shape and helps it resist stress

• Helps connect cells to neighboring cells

• In epidermal cells, they are made out of the tough protein keratin

• Gives hair and fingernails their strength

Cytoskeleton - Microtubules NOT PERMANENT STRUCTURES

• Holds organelles in place

• Forms bundles that maintain the cells shape and rigidity

• Enables motor proteins to walk along them, carrying organelles and macromolecules around the cell

• Forms the axoneme of cilia and flagella

• Forms the mitotic spindle that guides chromosomes during cell division

Centrioles

• A short cylindrical assembly of microtubules

• Arranged in nine groups of three microtubules each

• Two centrioles lie perpendicular to each other within a small clear area of cytoplasm called the centrosome

• Play a role in cell division

Cilia and Flagella

• Hair-like motile projections from free surfaces that help propel substances within body or allow locomotion

• Cilia are usually shorter and more numerous

  • found on the free surface of ciliated columnar epithelium

  • cilia moves mucus, ova, etc.

• Flagella are usually longer and less numerous

  • tail of sperm

Plasma Membrane

The cell and many of the organelles within it are bordered by a plasma membrane

• surrounding the cell at its periphery

• establishes boundary of cell

• establishes shape of cell

• establishes identity of cell

• regulates various vital metabolic reactions

Plasma Membrane Processes

Physiologically important processes occur at the surface of a cell

• immune responses

• binding of egg and sperm

• cell-to-cell signaling by hormones

• detection of tastes and smells

• regulation of the passage of materials in and out of the cell