section 1, chapter 3

Section 1, Chapter 3Cells

CellsOverview

Basic unit of life75 Trillion cells in human bodyVary in size and shapes

Over 260 types of cells in body i.e. neurons, muscle, bone, blood cells All types are derived from just 1 fertilized egg

DifferentiationForming specialized cells from unspecialized cells

Major Parts of a CellNucleus

Cell Membrane

CytoplasmCytosol = fluidOrganelles

Cell MembraneOverview

The cell membrane maintains integrity of cell

Membrane is a fluid structure – flexible

Selectively permeable- allows only select substances into and out of cell

Signal transduction – communication between cell & environment

The cell membrane is composed of three major components

1. Bilayer of phospholipids 2. Cholesterol 3. Membrane proteins

Polar region (hydrophilic)

Nonpolar region(hydrophobic)

Phospholipid bilayer

Phospholipid Bilayer

Nonpolar Hydrocarbon tailsPhospholipids align so that tails are hidden from water

Nonpolar tails form the interior of membrane

Polar Phosphate headsPolar groups align to face water

Polar heads are exposed to surfaces of membrane

Phospholipid bilayer forms a fluid, yet stable boundary.

The interior the cell membrane is hydrophobic

Permeable to nonpolar molecules Steroids, Oxygen, Carbon Dioxide can easily cross the membrane

Impermeable to polar moleculesProteins, Water, Sugars, ect. Cannot easily cross membrane

Cholesterol= rigid rings of hydrocarbons

Contributes to the nonpolar nature of membrane

Stabilizes the cell membrane

Increases rigidity of cell membrane

Membrane Proteins1. Integral Proteins

Spans cell membrane

Forms ion channels & pores

Examples include: Na+ channels and K+ channels Aquaporins = water channels

Transmembrane ProteinsIntegral protein, where one end extends outside cell, and the other end dips into cytoplasm.

Many function as receptors

Membrane Proteins2. Peripheral Proteins

Projects from surface of membrane

May be a glycoprotein (protein + sugar)

Includes Cellular Adhesion Molecules (CAM)

Membrane Proteins

Cellular Adhesion Molecules (CAM)

Guides moving cells to targets

Establishes cell-to-cell connectionsForms new neural connections in learning and memoryGuides cells surrounding an embryo towards uterusGuides white blood cells to injury

Selectin

• Covers the surface of white blood cells (WBC)

• Selectin binds to carbohydrates on surface of damaged capillaries

• Allows circulating WBCs to anchor near site of injury

CAM Protein

Transmembrane Protein Receptor

A molecule (ligand) binds to portion of receptor outside cell

Transmembrane Protein changes conformation

Portion inside cell sends a signal into cell

1. Nuclear Envelope

2. Nucleolus

3. Chromatin

3 Parts of the nucleus

• Double-layered membrane = 2 lipid bilayers.

• Nuclear Pores• Channel proteins allow specific

molecules across nuclear envelope

• Ribosomes & RNA leaves nucleus through pores

Nuclear Envelope

Nucleolus “little nucleus”

• Dense body of RNA & Proteins

• Produces Ribosomes

Chromatin “Colored substance”

Chromosome “colored body”

Condenses into chromosomes during mitosis

DNA wrapped around histone proteins

End of Section 1, Chapter 3