Introduction to Physiology: The Cell and General...

Copyright © 2006 by Elsevier, Inc.

Chapter 2:The Cell and Its Functions

Slides by Dr. Abbas S. Dakhil, Ph.D.


Organization of the Cell

• Cells: the basic structural and functional unit


The different substances that make up the cell are collectively calledprotoplasm. Protoplasm is composed mainly of five basic substances:.

• Water

• Electrolytes

• Proteins

• lipids

• Carbohydrates


Physical Structure of the Cell

The cell contains highlyorganized physicalstructures, calledintracellular organelles.


Membranous Structures of the Cell

The cell membrane iscomposed mainly of a lipidbilayer of phospholipidmolecules, but with largenumbers of proteinmolecules protrudingthrough the layer.Also, carbohydrate moietiesare attached to the proteinmolecules on the outside ofthe membrane and toadditional protein moleculeson the inside.


Endoplasmic Reticulum

granular endoplasmic reticulum contains ribosomes and they functionto synthesize new protein molecules

agranular, or smooth, endoplasmic reticulum. Synthesis of lipid substances


Golgi Apparatus

“transport vesicles” (also called endoplasmic reticulum vesicles, orER vesicles) and processed it to form lysosome and secretory vesicles



Lysosomes

• intracellular digestive system

• Lysosomes ingest (1) damaged cellular structures, (2) food particlesthat have been ingested by the cell, and (3) unwanted matter such asbacteria

• Contain 40 different hydrolase (digestive) enzymes


Peroxisomes

• Contain oxidases rather than hydrolases

• Oxidases are capable of combining oxygen with hydrogen ionsderived from different intracellular chemicals to form hydrogenperoxide (H2O2).

• H2O2 is a highly oxidizing substance and is used in associationwith catalase, another oxidase enzyme to oxidize many substancesthat might otherwise be poisonous to the cell


Secretory Vesicles

• secretory vesicles or secretory granules are formed by the endoplasmicreticulum–Golgi apparatus system and are then released from theGolgi apparatus into the cytoplasm.

• Secretory vesicles store protein proenzymes (enzymes that are notyet activated). The proenzymes are secreted later through the outercell membrane.


Mitochondria

• Mitochondrion is composed mainly of two lipid bilayer–proteinmembranes: an outer membrane and an inner membrane

• Many infoldings of the inner membrane form shelves onto whichoxidative enzymes are attached.

• In addition, the inner cavity of the mitochondrion is filled with amatrix that contains enzymes that are necessary for extractingenergy from nutrients.


Nucleus

• The nucleus is the control center of the cell

• The nuclear membrane (nuclear envelope), is separate bilayermembranes, one inside the other. The outer membrane is continuouswith the endoplasmic reticulum of the cell cytoplasm,


Functional Systems of the Cell

1. Ingestion by the Cell—Endocytosis

• The principal forms of endocytosis are pinocytosis and phagocytosis.

Mechanism of pinocytosis.



2. Digestion of Foreign Substances Inside the Cell—Function ofthe Lysosomes



Extraction of Energy from Nutrients—Function of theMitochondria

almost all these oxidative reactionsoccur inside the mitochondria, andthe energy that is released is used toform the high-energy compoundATP.• carbohydrates are convertedinto glucose• proteins are converted into

amino acids• fats are converted into fatty

acids



Functional Characteristics of ATP

ATP is a nucleotide composed of (1) the nitrogenous base adenine, (2)the pentose sugar ribose, and (3) three phosphate radicals.



Uses of ATP for Cellular FunctionAdenosine triphosphate (ATP) (formed in the mitochondrion) provideenergy for three major cellular functions: (1) membrane transport, (2)protein synthesis, and (3) muscle contraction.

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Introduction to Physiology: The Cell and General...

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