Cell Membranes

About This Chapter

• Functional compartments of the body • Biological membranes • Intracellular compartments • Tissues of the body • Tissue remodeling • Organs

• Three major cavities – Cranial – Thoracic – Abdominopelvic • Fluid-filled compartments – Circulatory system – Eyes – Cerebrospinal fluid (CSF)

ANATOMICAL: The Body Cavities

POSTERIOR ANTERIOR

Cranial cavity

Pleural sac Thoracic Pericardial cavity sac

Diaphragm

Abdominal cavity Abdominopelvic cavity Pelvic cavity

• Hollow organs – Heart – Lungs – Blood vessels – Intestines • Lumen – For some organs, not the internal environment

• Extracellular fluid (ECF) – Plasma – Interstitial fluid • Intracellular fluid (ICF)

Compartments Are Separated by Membranes

Pericardial Tissue membranes Phospholipid bilayers membrane have many cells. create cell membranes.

Cell

Heart Loose connective tissue

The pericardial sac is Seen magnified, the pericardial Each cell of the The cell membrane a tissue that surrounds membrane is a layer of flattened pericardial membrane is a phospholipid the heart. cells supported by connective has a cell membrane bilayer. tissue. surrounding it.

• Physical isolation • Regulation of exchange with the environment • Communication between the cell and its environment • Structural support

• Lipids and proteins • Fluid mosaic model

The Fluid Mosaic Model of Biological Membranes

Peripheral proteins can Glycoprotein be removed without disrupting the integrity This membrane- of the membrane. Transmembrane spanning protein proteins cross the crosses the membrane lipid bilayer. seven times.

Carbohydrate Extracellular Phospholipid heads fluid face the aqueous COOH intracellular and extracellular compartments. Lipid-anchored proteins Peripheral Lipid tails protein form the Cytoplasm interior layer Cytoskeleton proteins of the membrane. Phosphate Cell Intracellular Cholesterol molecules insert NH2 membrane fluid themselves into the lipid layer. Cytoplasmic loop

• Lipids – Phospholipids – Sphingolipids – Cholesterol • Phospholipid structures in water solutions – Micelle – Liposome – Bilayer of the cell membrane

Membrane Phospholipids

Membrane phospholipids form bilayers, Polar head (hydrophilic) micelles, or liposomes. They arrange themselves so that their nonpolar tails Stylized model Nonpolar fatty acid tail are not in contact with aqueous (hydrophobic) solutions such as extracellular fluid. can arrange themselves as

Phospholipid bilayer Micelles are droplets of phospholipids. Liposomes have forms a sheet. They are important in lipid digestion. an aqueous center.

• Proteins – Integral • Transmembrane • Lipid-anchored – Peripheral

• Carbohydrates – Glycoproteins – Glycolipids

• Cytoplasm – Cytosol – Inclusions – Cytoskeleton – Organelles • Nucleus

• Ribosomes – Fixed – Free • Polyribosomes

• Actin (microfilaments) • Intermediate filaments – Keratin – Neurofilaments • Microtubules – Centrioles, cilia, flagella

• Cell shape • Internal organization • Intracellular transport • Assembly of cells into tissues • Movement

• Centrosome – Assembles tubulin monomers into microtubules • Centrioles – Direct DNA movement in cell division • Cilia – Fluid movement across cells • Flagella – Cell (sperm) movement through fluid

Cilia Cilia and flagella have The beating of cilia 9 pairs of microtubules and flagella creates surrounding a central pair. fluid movement. Fluid movement

Flagellum Microtubules

Fluid movement

Cilium

Cell membrane

Cilia

Organelle

Motor protein ATP

Direction of movement

Cytoskeletal fiber

• Myosins – Muscle contraction • Kinesins and dyneins – Movement of vesicles along microtubules • Dyneins – Movement of cilia and flagella

• Two membranes create two compartments – Mitochondrial matrix • Unique DNA – Intermembrane space • Essential role in cellular ATP production

Mitochondria Outer membrane Mitchondria are spherical to elliptical organelles with a double Intermembrane space wall that creates two separate compartments within the organelle. The inner is surrounded by a membrane that folds into Cristae matrix leaflets called cristae. The intermembrane space, which lies Matrix between the two membranes, plays an important role in ATP production. Mitochondria are the site of most ATP synthesis in the cell.

• Rough ER – Ribosomes attached – Protein assembly and modification • Smooth ER – Synthesis of fatty acids, steroids, lipids – Modified forms in liver, kidney, muscles

Endoplasmic Reticulum (ER) and Ribosomes Rough ER The endoplasmic reticulum (ER) is a network of interconnected membrane tubes that are a continuation of the outer nuclear Ribosomes membrane. Rough endoplasmic reticulum has a granular appearance due to rows of ribosomes dotting its cytoplasmic surface. Smooth endoplasmic reticulum lacks ribosomes and Smooth ER appears as smooth membrane tubes. The rough ER is the main site of protein synthesis. The smooth ER synthesizes lipids and, in some cells, concentrates and stores calcium ions.