The Eukaryotic Cell: Structure and Function

• Prokaryotes – single celled organism that lacks

  a nucleus and membrane bound

  organelles. (bacteria)
• Eukaryotes – organisms that have a well

  developed nucleus enclosed with

  nuclear envelope.
• CELL MEMBRANE

  -Defines the boundary of the cell from

  intracellular fluid and extracellular fluid.

  -Controls the passage of materials in and

  out of the cells

  -Govern the interaction of the cell with

  other cells
• Fluid Mosaic Model

  -Two layered phospholipid bilayer

  membrane with anchored proteins
• Phospholipids

  -Constitute 75% of membrane lipids

  -Occur as two layers (phospholipid

  bilayer)
• Three types of membrane lipids: phospholipids, cholesterol, glycolipids
• Composition of Phospholipid:

  Head – glycerol and phosphate unit,

  hydrophilic and faces the fluid part of the cell.

  Tail – two fatty acid chains,

  hydrophobic; oriented away from the fluid part

  of the cell.
• Cholesterol

  -Constitute 20% of the membrane lipids

  -Gives fluidity to the cell membrane
• Glycolipids

  -Constitute 5% of the membrane lipids

  -2 fatty acids + short carbohydrate

  chains
• Two Kinds of membrane proteins: Integral and peripheral
• Integral Proteins

  -Pass all the way through the cell

  membrane
• Peripheral Proteins

  -Adhere to the surface of the cell

  membrane

  -Glycoprotein – protein + short

  carbohydrate chains
• Receptors – bind to chemical

  messengers such as hormones, bind to

  receptor results to a physiological

  change in the cell, and important cell

  for communication.
• Enzymes – act as catalysts for chemical

  reaction to take place.
• Anchor proteins – physically link

  intracellular structures.
• Three kinds of transport proteins: channel, carrier, and pump
• Channel Protein – allow the passage of

  water and solutes to enter or exit the

  cell.
• Carrier Protein – transport substances

  into and out of the cell; can change its

  orientation
• Protein Pumps – transport substances

  against its concentration gradient.
• Fluidity of Membranes

  -Permits movement of membrane pieces

  -Allow vesicle formation and fusion
• Exocytosis – release of materials

  outside (secretion)
• Endocytosis – materials taken inside

  o Phagocytosis – solid

  o Pinocytosis – liquid
• Compartmentalization -each compartment is specialized for a particular process producing a particular

  substance.
• Hydrophobic substances, smaller

  molecules like water may diffuse

  easily through the phospholipid

  bilayer.
• Large hydrophilic substances like

  amino acid, glucose, and ions

  need to pass through membrane

  proteins by facilitated diffusion or

  active transport.
• PROTOPLASM

  -All substances inside the cell membrane

  except the vacuole; incudes the

  nucleus and the cytoplasm.
• CYTOPLASM

  -Part between the cell membrane,

  nucleus and or the vacuole.
• Cytosol – fluid portion that contains

  water, dissolved solutes and

  suspended particles.
• Organelles – subcellular structures
• Membranous Organelles

  -Surrounded by one or two bilayer lipid

  membrane

  -Includes the endomembrane system
• Non-Membranous Organelles

  -Lack membranes and directly in

  contact with the cytosol
• NUCLEUS

  -Spherical structure with double layered

  membrane

  o Outer membrane continuous with

  the rough endoplasmic reticulum

  o With nuclear pores for the

  passage of substances between

  the nucleus and the cytoplasm
• Nucleoli – involved in the synthesis of

  ribosomes
• Chromatin - tightly coiled DNA and

  histone proteins
• Nucleoplasm – fluid substance

  containing water, enzymes and RNA
• ENDOPLASMIC RETICULUM

  -Extensive membranous network

  continuous with the nuclear membrane
• Rough Endoplasmic Reticulum

  -With ribosomes

  -Synthesize proteins for secretion
• Smooth Endoplasmic Reticulum

  -Lacks ribosomes

  -Synthesize membrane lipids
• GOLGI APPARATUS (DICTYOSOMES)

  -Consists of flattened membrane sacs

  which receive protein from ER or lipids

  from SER

  o Form vesicles that process, sort

  and package proteins/lipids for

  transport to different parts of the

  cell or for secretion
• Cis Face – entry side of dictyosome