the cell and its function

8/10/2019 The Cell and Its Function

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THE CELL AND ITS FUNCTIONS.M REYES, DMD


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INTRODUCTION TO PHYSIOLOGY: THE CELL AND GEN

PHYSIOLOGY

1. THE FUNCTIONAL ORGANIZATION OF THE HUMAN BODY AND CONTROL OF IN

ENVIRONMENT

2. THE CELL AND ITS FUNCTION

3. GENETIC CONTROL OF PROTEIN SYNTHESIS ,CELL FUNCTION AND CELL REPR


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THE CELL


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ORGANIZATION OF THE CELL

two major parts of the cell :

nucleus- separated from the cytoplasm by a nuclear membrane

Cytoplasm- separated from the surrounding fluids by a cell membrane, also called the plasma

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

water, electrolytes, proteins, lipids, and carbohydrates.


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PARTS OF THE CELL


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PROTOPLASM IS COMPOSED MAINLY OF FIVE BASIC

SUBSTANCES

Water. The principal fluid medium of the cell ,which is present in most cells, except for

concentration of 70 to 85 per cent.

Ions. The most important ions in the cell are potassium,magnesium,phosphate, sulf

bicarbonate, and smaller quantities of sodium, chloride, and calcium.

Proteins. Second most abundant substances in most cells ,constitute 10 to 20 per cen

mass.

Lipids. phospholipids and cholesterol constitute only about 2 per cent of the total cell m

in water ,used to form the cell membrane and intracellular membrane barriers that sepa

cell compartments.

Carbohydrates play a major role in nutrition of the cell, i.e glycogen


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PHYSICAL STRUCTURE OF THE CELL


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The cell is not merely a bag of fluid, enzymes, and chemicals; it also contains highly org

structures, called intracellular organelles.

The physical nature of each organelle is as important as the cells chemical constituent

For instance, without one of the organelles,the mitochondria, more than 95 per cent of

release from nutrients would cease immediately


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1. Membranous Structures of

the Cell

2. Cytoplasm and Its Organelles


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1. MEMBRANOUS STRUCTURES OF THE CELL

Cell membrane

also called the plasma membrane, envelops the cell, is a thin, pliable, elastic structure only 7.

thick.

It is composed almost entirely of proteins and lipids

The approximate composition is :

proteins,55 per cent phospholipids, 25 per cent

cholesterol, 13 per cent

other lipids, 4 per cent

carbohydrates,3 per cent


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LIPID: BARRIER OF THE CELL MEMBRANE AND IMPE

WATER PENETRATION

The basic lipid bilayer is composed of PHOSPHOLIPID molecules.

Each layer has two ends:

Hydrophilic or the phosphate portion

Hydrophobic or the fatty acid portion

hydrophobic portions of the phospholipid molecules are repelled by water but are mutu

one another,they have a natural tendency to attach to one another in the middle of the

hydrophilic phosphate portions then constitute the two surfaces of the complete cell me

intracellular water on the inside of the membrane

extracellular water on the outside surface.


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PHOSPHOLIPID BILAYER


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CHOLESTEROL MOLECULES IN THE CELL MEMBRAN

also lipid in nature

Dissolved in the bilayer of the membrane.

They mainly help determine the degree of permeability (or impermeability) of the bilaye

constituents of body fluids.

Cholesterol controls much of the fluidity of the membrane as well.


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PROTEINS IN THE CELL MEMBRANE

Two types of proteins occur: 1. integral proteins-protrude all the way through the membrane

2. peripheral proteins- attached only to one surface of the membrane and do not penetrthrough.


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FUNCTIONS OF INTEGRAL PROTEINS

1. provide structural channels (or pores) through which water molecules and water-solu

especially ions, can diffuse between the extracellular and intracellular fluids

2. act as carrier proteins for transporting substances that otherwise could not penetrate

3. transport substances in the direction opposite to their natural direction of diffusion, w

active transport

4. act as enzymes


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INTERGRAL PROTEINS AND PERIPHERAL PROTEINS


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FUNCTION OF PERIPHERAL PROTEINS

Act as enzymes or as controllers of transport of substances throu

membrane pores.


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CARBOHYDRATES IN THE CELL MEMBRANEGLYC

Proteoglycansare carbohydrate substances bound to small protein coresare loosel

outer surface of the cell as well.

Thus, the entire outside surface of the cell often has a loose carbohydrate coat called t

functions of the Glycocalyx:

(1) a negative electrical charge, that repels other negative objects.

(2) The glycocalyx of some cells attaches to the glycocalyx of other cells, thus attachin

another.

(3) Many of the carbohydrates act as receptor substances for binding hormones

(4) Some carbohydrate moieties enter into immune reactions


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1. Membranous Structures of the Cell

2. Cytoplasm and Its Organelles


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CYTOPLASM

filled with both minute and large dispersed particles and organelles.

The clear fluid portion of the cytoplasm in which the particles are dispersed is called

Dispersed in the cytoplasm are :

neutral fat globules

glycogen granules

Ribosomes

secretory vesicles,

five especially important organelles: 1. the endoplasmic reticulum, 2. the Golgi apparatus, 3.mlysoSomes, and 5. peroxisomes.


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FIVE ESPECIALLY IMPORTANT ORGANELLES:

1. the endoplasmic reticulum

2. the Golgi apparatus

3. Mitochondria

4. Lysosomes

5. Peroxisomes.


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1. ENDOPLASMIC RETICULUM

network of tubular and flat vesicular structures

The space inside the tubules and vesicles is filled with endoplasmic matrix, a watery

different from the fluid in the cytosol

provide machinery for a major share of the metabolic functions of the cell

TWO TYPES OF ER:

1. Granular Endoplasmic Reticulum- Ribosomes, synthesize new protein molecules in the cel

2. Agranular Endoplasmic Reticulum- synthesis of lipid substances


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GRANULAR AND AGRANULAR ENDOPLASMIC RETICU


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GOLGI APPARATUS

composed of four or more stacked layers of thin,flat,enclosedvesicles lying near one s

nucleus

The Golgi apparatus functions in association with the endoplasmic reticulum. HOW?

transport vesicles (also called endoplasmic reticulum vesicles,or ER vesicles) pinch o

endoplasmic reticulum and fuse with the Golgi apparatus.

The transported substances are then processed in the Golgi apparatus to form lysosomes

secretory vesicles

other cytoplasmic components


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GOLGI APPARATUS


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LYSOSOMES

vesicular organelles that form by breaking off from the Golgi apparatus and then disper

the cytoplasm

contains hydrolase (digestive) enzymes.

Functions:

(1) digests damaged cellular structures

(2)digests food particles that have been ingested by the cell

(3)digests unwanted matter such as bacteria


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LYSOSOMES


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PEROXISOMES

formed by self-replication (or perhaps by budding off from the smooth endoplasmic retic

than from the Golgi apparatus.

contain oxidases rather than hydrolases

oxidases are capable of combining oxygen with hydrogen ions derived from different in

chemicals to form hydrogen peroxide (H2O2).

Hydrogen peroxide is a highly oxidizing substance ,functions to oxidize many substanotherwise be poisonous to the cell

i.e. about half the alcohol a person drinks is detoxified by the peroxisomes of the liver cells in t


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MITOCHONDRIA

powerhouses of the cell.

Mitochondria is self-replicative

composed mainly of two lipid bilayerprotein membranes:

an outer membrane

an inner membrane- form shelves onto which oxidative enzymes are attached

the inner cavity is filled with a matrix(contains large quantities of dissolved enzymes)

extracting energy from nutrients.

Theseenzymes operate in association with the oxidative enzymes on the shelvest

oxidation of the nutrientsformation of 1. carbon dioxide and water 2. releasing ener


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MITOCHONDRIA


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ATP FUNCTION

ATP releases its energya phosphoric acid radical is split away = formation of adenos

(ADP)

This released energy is used to energize vir tually all of the cells other functions, such

substances and muscular contraction.

To reconstitute the cellular ATP as it is used up,

energy derived from the cellular nutrients causes ADP and phosphoric acid to recombine to fo

the entire process repeats over and over again.

Hence ,ATP has been called the energy currency of the cell


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SECRETORY VESICLES

Formed by the endoplasmic reticulumGolgi

apparatus system and are then released from

the Golgi apparatus into the cytoplasm in the

form of storage vesicles


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SECRETORY VESICLE


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FILAMENT AND TUBULAR STRUCTURES OF THE CEL

primary function

act as a cytoskeleton, providing rigid physical structures for certain parts of


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NUCLEUS

control center of the cell.

contains large quantities of DNA, which are the genes.

The genes determine the characteristics of the cells proteins,including the structural pr

the intracellular enzymes that control cytoplasmic and nuclear activities.

The genes also control and promote reproduction of the cell itself.

The genes first reproduce to give two identical sets of genesthen the cell splits by a s

called mitosisto form two daughter cells,each of which receives one of the two sets of


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NUCLEUS


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NUCLEAR MEMBRANE

also called the nuclear envelope,

has two separate bilayer membranes, one inside the other.

The outer membrane is continuous with the endoplasmic reticulum and the space betw

nuclear membranes is also continuous with the space inside the endoplasmic reticulum The nuclear membrane is penetrated by several thousand nuclear pores


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NUCLEOLI AND FORMATION OF RIBOSOMES

Nucleolus does not have a limiting membrane.

It is the accumulation of large amounts of RNA and proteins of the

found in ribosomes.

The nucleolus becomes considerably enlarged when the cell is ac

synthesizing proteins.


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NUCLEOLI AND FORMATION OF RIBOSOMES

Formation of the nucleoli (and of the ribosomes in the cytoplasm

nucleus) begins in the nucleus. How?

Specific DNA genes in the chromosomescause synthesis of R

Some of the RNA is stored in the nucleoli

most of the RNA is transported outward through the nuclear pores into cytop

Here, it is used in conjunction with specific proteins to assemble mature ribosom

essential role in forming cytoplasmic proteins


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FUNCTIONAL SYSTEMS OF THE CELL


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INGESTION BY THE CELLENDOCYTOSIS

If a cell is to live and grow and reproduce, it must obtain nutrients and other substancessurrounding fluids.

Most substances pass through the cell membrane by diffusion and active transport.

Endocytosis a specialized function of the cell membrane which allows very large part

cell

Two types Endocytosis

Pinocytosis - ingestion of minute particles that form vesicles of extracellular fluid and particinside the cell cytoplasm.

Phagocytosismeans ingestion of large particles, such as bacteria, whole cells, or portions of

tissue.


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MECHANISMS OF PINOCYTOSIS

DIGESTION OF PINOCYTOTIC AND PHAGOCYTIC FOR


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SUBSTANCES INSIDE THE CELLFUNCTION OF THE

LYSOSOMES

After a pinocytotic or phagocytic vesicle appears inside a cell, one or more lysosomes b

to the vesicle and empty their acid hydrolases to the inside of the vesicledigestive v

residual body- remnant of the digestive vesicle

Residual body is excreted through the cell membrane by a process called EXOCYTOS



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LYSOSOMES



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LYSOSOMES

Regression of Tissues and Autolysis of Cells Tissues of the body often regress to a smaller size, Lysosomes are responsible for much of thi

I.E Uterus after pregnancy, in muscles during long periods of inactivity, and in mammary glandlactation

The lysosomes also contain bactericidal agents that can kill phagocytized bacteria befocause cellular damage.

(1) lysozyme, dissolves the bacterial cell membrane;

(2) lysoferrin, prevents bacterial growth

(3) acid at a pH of about 5.0, which activates the hydrolases and inactivates bacterial metabol


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LOCOMOTION OF CELL

Two other types of movement

ameboid locomotion

ciliary movement


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1. AMEBOID MOVEMENT

movement of an entire cell in relation to its surroundings, such as movement of white b

through tissues

Mechanism of ameboid locomotion:

1.Begins with protrusion of a pseudopodium from one end of the cell

2.The pseudopodium projects far out, away from the cell body, and partially secures its

tissue area.

3. Then the remainder of the cell is pulled toward the pseudopodium


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AMEBOID MOVEMENT


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Types of cell that exhibit amoeboid locomotion

1. white blood cells when they move out of the blood into the tissues in the form of tissue ma

2. fibroblasts move into a damaged area to help repair the damage

3. embryonic cells often must migrate long distances from their sites of origin to new areas dof special structures.


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Chemotaxis

Controls Ameboid Locomotion

most important initiator of ameboid locomotion

results from the appearance of certain chemical substances in the tissues- chemotactic substa


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2. CILIA AND CILIARY MOVEMENTS

A second type of cellular motion

whiplike movement of cilia on the surfaces of cells.

Occurs in only two places in the human body:

1. surfaces of the respiratory airways 2. inside surfaces of the uterine tubes

the cell and its function

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