Chapter 3 Marieb Human Anatomy and Physiology - Lecture Notes | BIOL 2403, Study notes of Physiology

Download Chapter 3 Marieb Human Anatomy and Physiology - Lecture Notes | BIOL 2403 and more Study notes Physiology in PDF only on Docsity!

THE CELLULAR LEVEL OF ORGANIZATION

Chapter 3

Anatomy and Physiology Lecture

THE CELLULAR LEVEL OF ORGANIZATIOM

Functions of the Cell

1. Basic unit of life
2. Protection and Support
3. Movement
4. Communication
5. Cell metabolism and energy release
6. Inheritance

How We See Cells

1. Light microscope
2. Electron microscope
3. Scanning electron microscope (SEM)
4. Transmission electron microscope (TEM)

Summary of Cell Parts

1. Plasma membrane. The outer, limiting membrane separating the cell's internal parts from the extracellular materials and external environment.
2. Cytoplasm: Cytoplasm. The substance that surrounds organelles and is located between the nucleus and the plasma membrane. All cellular contents located between plasma membrane and nucleus. Cytosol - the thick semifluid portion of the cytoplasm; which is intracellular fluid.
3. Cytoplasm: Organelles. Permanent structures with characteristic morphology that are highly specialized for specific cellular activities.
4. Nucleus. The secretions and storage products of cells.

Polar part is the phosphate-containing “head”, which is hydrophilic (mixes with water).

Nonpolar parts are the two fatty acid “tails”, which are hydrophobic (do not mix with water).

(b) Glycolipids (Combination of Carbohydrate and Lipids) consist of 5% of membrane lipids.

Glycolids, like phospholids are also amphipathic.

Functions: (1) Are important for adhesion among cells and tissues. (2) May mediate cell-to-cell recognition and communication. (3) Contribute to regulation of cellular growth and development.

(C) Cholesterol molecules ( a lipid) consists of 20% of membrane lipids.

Cholesterol molecules are on both sides of the bilayer, located among the phospholipids in animal cells.

The stiff steriod rings of cholesterol strengthen the membrane but decrease its flexibility.

• Plant cell membranes lack cholesterol.

• (Bilayer is self-healing; if a needle is pushed through it and pulled out, the puncture site seals).

Membrane Proteins

Fluid-mosaic model – Is the modern concept of the plasma membrane that suggests that the plasma membrane is neither rigid nor static in structure, but highly flexible and can change its shape and composition through time.

Membrane Proteins are classified into two categories: Integral (intrinsic) and Peripheral (extrinsic) proteins:

(a) Integral Proteins extend across the phospholipid bilayer among the fatty acid tails.

Are Glycoproteins (combination of sugar and protein)

Functions of Integral:

1. Some integral Protein (glycoprotein) form tiny channels (pores) through which certain subs flow into or out of the cell.
2. Others act as transporter (carriers) to move a substance from one side of the membrane to the other.
3. Serve as recognition sites called receptors.

(b) Peripheral Proteins do not extend across the phospholipid bilayer.

Are loosely bound to the inner and outer surface of the membrane and are easily separated from it.

(Far less is known about Peripheral Protein than Integral Protein, and their functions are not yet completely understood.)

Generalized Functions of Membrane Proteins

1. Channel (Pore)
2. Transporter (carrier)
3. Receptor
4. Enzyme
5. Cytoskeleton anchor
6. Cell identity marker

Marker Molecules

Marker Molecules are cell surfaces molecules that allow cells to identify one another or other molecules.

MOVEMENT THROUGH THE PLASMA MEMBRANE

Extracellular materials are separated from the Intracellular materials by the Plasma membrane. A Plasma membranes is Selectively Permeable , that is, it allows only certain substances to pass through it.

In order for cells to survive, thing must move in and out of the cell.

Certain substances, for example, must move into the cell to support life, whereas waste materials or harmful substances must be moved out.

Four Ways By Which Substances Can Pass Through Plasma Membrane :

1. Directly through the phospholipid membrane
2. Membrane channel
3. Carrier molecules
4. Vesicles

Two processes involved in movement of material are:

1. Passive (physical) Processes - the substance move on their own down a concentration gradient; that is, from an area where their concentration is high to an area where their concentration is low.

*(Mechanisms that move substances across a membrane without using energy (released by splitting ATP).

The substance may also be forced across the plasma membrane by pressure from an area where the pressure is high to an area where it is low.

*Without an expenditure of energy.

2. Active (Physiological) Processes - the substance does not move on its own. The substance moves against a concentration gradient, that is, from an area where its

concentration is low to area where it is high.

*(Mechanism that move substances across a membrane by using energy released by splitting ATP).

*With an expenditure of energy.

Mechanism that move substances across a membrane by using energy (released by splitting ATP).

Diffusion

Diffusion is the movement of solutes from an area of higher concentration to an area of lower concentration in solution.

Net Diffusion - the difference in diffusion between two regions having different concentration.

Equilibrium - point of even distribution.

Concentration Gradient is the difference between high and low concentration.

Viscosity is a measure of how easily a liquid flows; thick solutions, such as syrup. Are more viscous than water. Diffusion occurs more slowly in viscous solvents than in thin watery solvents.

(Molecules moving from the high-concentration area to the low- concentration area are said to move down or with the concentration gradient.)

Note: Diffusion of molecules is an important means by which substances move between the extracellular and intracellular fluids in the body.

Example of diffusion in the body: The movement of oxygen from the blood

-Water molecules move out of the cells faster than they can enter, causing the red blood cells to shrink.

-Shrinkage of red blood cells in this manner is called crenation. *(2% NaCl solution is Hypertonic solution.)

Filtration

Filtration is the movement of solvents (water) and dissolved substances (solute) across a selectively permeable membrane by gravity or hydrostatic (water) pressure.

From area of high pressure to an area of lower pressure.

Example in the body: Occurs in the kidney, where the blood pressure supplied by the heart forces water and small molecules like urea through thin cell membranes of tiny blood vessels and into the kidney tubules.

*(Protein molecules remain in the blood since they are too large to be forced through the cell membrane of the blood vessels).

(Molecules of many harmful substances and waste products are small enough to be filtered. They then can be eliminated in the urine).

MEDIATED TRANSPORT MECHANISM

Mediated transport mechanism involves carrier proteins within the plasma membrane that move large, water-soluble molecules or electrically charged molecules across the plasma membrane.

Specificity means that each carrier protein binds to and transports only a single type of molecule.

Competition is the result of similar molecules binding to the carrier protein.

Saturation means that the rate of transport of molecules across the membrane is limited by the number of available carrier proteins.

Three Kinds of Mediated Transport:

1. Facilitated Diffusion

Facilitated Diffusion - Is a carrier-mediated process that moves substances into or out of cells from a higher to a lower concentration.

Does not require metabolic energy to transport substance across the plasma membrane.

*Facilitated diffusion of glucose - is greatly accelerated by insulin , a hormone produced by the pancreas.

2. Active Transport

Some substances cannot move (enter or leave) into the cell either because they are too big, have the wrong charge, or must move against the concentration gradient.

Active Processes - Is a mediated transport process that requiresenergy provided by ATP.

Active transport processes are important because they can move substances against their concentration gradients, that is, from lower concentration to higher concentration.

Example: The Sodium Pump

Sodium Pump maintains a low concentration of sodium ion (Na+) in the cytosol (intracellular fluid) by pumping then out against their concentration gradient.

Also move Potassium ions (K+) into cells against their concentration gradient.

Vesicle – Is a membrane-bounded sac found within the cytoplasm.

1. Phagocytosis or "cell eating " - projections of the plasma membrane and cytoplasm (psuedopods) surround large solid particles outside the cell and then engulf them.

Phagocytic white blood cells and cells in other tissues engulf and destroy bacteria and other foreign substances; which constitutes a vital defense mechanism to protect us from disease.

2. Pinocytosis or "cell drinking " - the engulfed material is a tiny droplet of extracellular fluid rather than a solid.
3. Receptor-Mediated Endocytosis - similar to pinocytosis, but a highly selective process in which cells can take up specific molecules or particles.

Large molecules (eg. ligands) bond with receptors (specific proteins) and cross the plasma membrane.

Example: The virus that causes AIDS enters cells by attaching to a glycoprotein receptor called CD4 that is present on certain types of white blood cells.

Exocytosis - is a reverse process; it discharges substances from cells.

Occurs in all cells but is especially important in nerve cells, which release their neurotransmitter substances by this process.

CYTOPLASM

Cytosol

Cytosol : Consist of a fluid portion, a cytoskeleton, and cytoplasmic inclusions.

Cytoskeleton – Support the cells and holds the nucleus and organelles in place.

Cytoskeleton Consists of Three Groups of Protein

1. Microtubles: Are large hollow tubules composed primarily of protein units called tubulin.
2. Actin filament or Microfilaments: Are small fibrils about 8 nm in diameter that form bundles, sheets, or networks on the cytoplasm of cells.
3. Intermediate filaments: Are protein fibers about 10 nm in diameter that provide mechanical strength to cells.

Cytoplasmis Inclusions – Are aggregates of chemicals either produced by the cell or taken in by the cells.

ORGANELLES

Nucleus (Think of “Brain” or “Control Tower”)

The largest structure in the cell; spherical or oval in shape.

Contains the hereditary factors of the cell, called genes, which control cellular structure and direct many cellular activities.

Contains genetic material which consists of deoxyribonucleic acid (DNA).

Genetic material appears as a threadlike called Chromatin; when cell is not reproducing.

Prior to cellular reproduction the chromatin shorten and coils into a rod- shaped bodies called chromosomes.

Nucleoli are present inside the nucleus.

2. Agranular (smooth) ER

-Do not contain ribosomes -Synthesize fatty acid, phospholipid, and steroid -Can inactivate or detoxify a variety of channels, including alcohol, pestiudes, and carcinogens

Golgi Complex (Think of a “post office”)

Consists of four to six stacked, flattened membranous sacs (cisternae) referred to as cis, medial, and trans cisternae.

Process, sort, and deliver proteins within the cell.

Secretes proteins and lipids and forms lysosomes.

Mitochondria (Think of “Powerhouse”)

Are called the "Powerhouses" of the cell, as they function in energy generating.

Active cells, such as muscle, liver, and kidney tubule cells, have large number of mitochondria because of their high energy expenditure.

Within mitochondria, energy is transferred from carbon compounds, such as glucose, to ATP.

Mitochondria is composed of two membranes

a. The outer mitochondria membrane is smooth, but the inner membrane is arranged in a series of folds called cristae.

b. The central cavity of a mitochondrion enclosed by the inner membrane and cristae is called the matrix.

Lysosomes (Think of “Suicide packets”)

Are formed from Golgi complexes.

Function in Intracellular Digestion:

Contain digestive enzymes; digest worn-out organelles by a process called autophagy (self-eat)

Digests injured cell by a process called autolysis (self-destruct).

Lysosomes are thereby called "suicide packets"

Are found in large numbers in white blood cells, which carry on phagocytosis (cell eating).

Functions in Extracellular Digestion

-(Prior to fertilization, the head of a sperm cell releases lysosomal enzymes capable of digesting a barrier around the egg so that the sperm cell can penetrate it.)

-Involved in bone removal (especially during the growth process)

Peroxisomes

Similar in structure to lysosomes, but smaller.

Are abundant in liver cells.

Contain several enzymes (e.g. catalase) involved in the metabolism of hydrogen peroxide.

Catalase 2H 2 O 2 --------------------------- 2H 2 O + 2O 2 Hyrdogen Water Oxygen

-It protects the body by screening out harmful ultraviolet rays from the sun.

2. Glycogen - a polysaccharide that is stored in the liver, skeletal muscle fibers (cells), and the vaginal mucosa.

-When the body requires quick energy, liver cells can break down the glycogen into glucose and release it.

3. Lipids - are stored in adipocytes (fat cells), may be decomposed for producing energy.

Extracellular materials

-Are substances that lie outside the plasma membrane. -They provide support and a medium for the diffusion of nutrients and wastes. -Some, like hyaluronic acid and chondroitin sulfate, are amorphous (without shape). -Others, like collagenous, reticulae, and elastic fibers, are fibrous.

OVERVIEW OF CELL METABOLISM

Cell Metabolism – Is the sum of all the catabolic (decomposition) and anabolic (synthesis) reactions in the cell.

Glycolysis – Converts the glucose to Pyruvic acid.

Aerobic respiration – Occurs when oxygen is available.

Anaerobic respiration – Occurs without oxygen and includes the conversion of Pyruvic acid to lactic acid.

GENE ACTION

Gene is a group of nucleotides on a Deoxyribonucleic Acid (DNA) molecule that serves as the master mold for manufacturing a specific protein.

Cells are basically protein factories that constantly synthesize large numbers of diverse proteins.

Proteins , in turn determine the physical and chemical characteristics of cells and therefore of organisms.

Other proteins serve as hormone, antibodies, and contractile elements in muscle tissue. Others are enzymes.

Deoxyribonucleic Acid (DNA ) is a substance present in nuclei of cells consisting of phosphoric acid, a sugar, and nitrogenous bases.

-It is a nucleic acid localized principally in the chromosomes.

-It regulates protein synthesis and is the key molecule of the genes which give each cell its hereditary qualities and characteristics.

PROTEIN SYNTHESIS

Production of all the Proteins in the body is under the control of DNA.

Building blocks of DNA are nucleotides containing: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

Triplet (every three nucleotides), code for an amino acid, and amino acids are the building block of proteins.

Genes – Are all of the triplets required to code for the synthesis of a specific protein.