Chapter 3: The Cellular Level of Organization

Cell Membrane

• Composed of phospholipids, cholesterol, and membrane proteins

• Functions: structural support, physical isolation, create gradients, regulates exchange, sensing the extracellular environment

Phospholipids

• Diglycerides attached to a phosphate group

• Hydrophilic head (nonlipid and phosphate group) and hydrophobic tail (fatty acid)

Integral Proteins

Span the width of the membrane

cannot be removed without damaging membrane

Peripheral proteins

Bound to the inner or outer surface of the membrane

Anchoring Proteins

attach other structures to the plasma membrane

stabilize the membrane

Recognition proteins

identify the cell

Receptor proteins

Binds substances or ligands

Carrier proteins

transport polar solutes using energy

Channel proteins

allow water ions across the membrane. no energy required

Glycoproteins

Big protein, small glycan group

Proteoglycans

Small proteins, very large glycan groups

Cytoplasm

Holds all the internal components of the cell

Cytoskeleton

Dynamic internal scaffolding

Composed of:

• microfilaments: make a cytoplasmic network and attach to the plasma membrane

• Intermediate filaments: strengthen the cell

• Microtubules: support and movement to the organelles

Microvilli

• Finger shaped projections of the plasma membrane that increase surface area

• Cover the surface of the cell

Centrioles

• Direct the movement of chromosomes during cell division

Cilia

Contain microtubules at the core

Beat rhythmically to move fluids across cell surface

Ribosomes

• Responsible for manufacturing proteins

• Free floating: make cytoplasmic proteins

• Fixed onto the ER: make secreted and membrane proteins

Endoplasmic Reticulum

Rough ER: contains ribosomes, synthesizes and packs proteins in vesicles that are delivered to the Golgi apparatus

Smooth ER: Involved in lipid and carbohydrate synthesis

Golgi Apparatus

Modifies and packages secretions

Renews or modifies the plasma membrane

Packages lysosomes and other vesicles

Proteasomes

Degrades damaged or abnormal proteins in the cytoplasm or ER

Proteins are tagged with ubiquitin

Lysosomes

Degrades endocytosed proteins, organelles, or the entire cell

When does lysosome activation occur?

1. The primary lysosome fuses with the membrane of another organelle

2. The primary lysosome fuses with an endosome containing fluid or solid material from outside the cell

3. The lysosomal membrane breaks down during apoptosis following injury to the cell

Mitochondria

• Responsible for ATP production through aerobic respiration,

Nucleus

• Control center for the cell

• Stores all the information required to make different proteins

• Surrounded by a double membrane with large pores

• Nuclear membrane connects with the ER

• Contains DNA and produces mRNA

• Nucleoli: region of the nucleus that produces ribosomal RNA

Protein Synthesis:

DNA transcription creates mRNA

Translation occurs in ribosomes to create the amino acid sequence

Translation

Sequence of codons determines the sequence of amino acids

Complementary base pairing of anticodons (tRNA) provides the amino acids acids