College of Teacher Education

CELL PARTS AND FUNCTIONS

Cell Parts and Functions

Cell Parts and FunctionsMitochondria – the powerhouse of the

cell. It converts the potential energy of food molecules into ATP.

Microfilaments – also called actin filaments that are found just beneath the cell membrane providing support and maintaining cell shape.

Lysosome- the suicidal bag of the cell for it contains hydrolytic enzymes that can break down large macromolecules and also engulfs another organelle specially the damaged ones.

Cell Parts and FunctionsPeroxisome- contains enzymes that

can help detoxify alcohol and other harmful substances and convert poisonous peroxides to water. It also plays an important role in the hydrolysis of fatty acids into simple units that can be utilized by the mitochondria for the process of cellular respiration.

Centrioles – associated with the formation and anchoring of the spindle fibers during cell division of animal cell

Cell Parts and FunctionsMicrotubules – plays an important role

in intracellular transport, formation of mitotic spindle fiber needed for the cell division, and formation of cell wall in plant cells.

Smooth Endoplasmic Reticulum – performs functions like lipid synthesis, carbohydrate metabolism, and help in the detoxification of drug and poison.

Cell Parts and FunctionsGolgi apparatus – performs unique

functions of manufacturing, processing, and packaging macromolecules like protein and other products and secretions before they are sent to their respective destinations.

Cilia – structures for locomotion of cellRibosomes- these are where proteins

are manufactured. They are the protein factories of the cell.

Cell Parts and FunctionsRough Endoplasmic Reticulum-

provides surface for ribosomes where synthesis of many secretory proteins takes place.

Chromatin- to package DNA into a smaller volume to fit in the cell, to strengthen the DNA to allow mitosis, to prevent DNA damage, and to control gene expression. It contains the gene as well.

Cell Parts and FunctionsNucleus- contains the genetic material

that directs the production of protein and other many cellular processes. It is the central command of the cell center of the cell. Its main function is to control gene expression and initiate DNA replication.

Nuclear Envelope- protects the nucleus.

Cell Parts and FunctionsNucleolus- it is where components of

ribosomes and Rrna are synthesized. These components pass through the nuclear membrane into the cytoplasm where they are combined to form ribosomes.

Nuclear Pores – allows the passage of small water-soluble molecules in and out of the nucleus.

Cell Parts and FunctionsCytoplasm/ Plasma Membrane- the

region found outside the nucleus surrounded by cell membrane. This contains semifluid translucent substance called cytosol. Important cellular processes such as cell division take place in the cytoplasm. Suspended in the cytoplasm are membrane-bound organelles each performing specific functions all directed for the survival of the cell and the cell and the individual as a whole.

Cell Parts and FunctionsCell Membrane – a dynamic membrane

separating the interior of the cell from the outside environment. Aside from enclosing the cell, it gives form and shape to the cell. It is semi-permeable.

Plant Cell

College of Teacher Education

TRANSPORT ACROSS MEMBRANES

2 Major Kinds of Cell Transport1. Passive Transport – it is the

movement of molecules without the expenditure of energy.

2. Active Transport - it is the movement of molecules where energy is exerted by the cell.

3 Ways of Traversing the Cell Membrane

A substance may traverse the cell membrane in three principal ways:1. By Diffusion and Osmosis2. By Carrie-Mediated Transport System3. By Endocytosis

I.DIFFUSION The movement of particles from an

area of a higher concentration to an area of lower concentration of the particles or molecules, thus tending

3 Ways of Traversing the Cell Membrane

to equalize the concentrationthroughout the area of diffusion.

Simple Diffusion – the particle is transported through the membrane without the aid of permease and without expenditure of energy by the cell.

3 Ways of Traversing the Cell Membrane

II. OSMOSISIt is the movement of water molecules

or solvents through a semi-permeable membrane from a lower osmotic pressure to greater osmotic pressure

Osmotic Pressure – the physical pressure that exactly balances the osmosis of water due to the concentration difference between a solution and pure water.

3 Ways of Traversing the Cell Membrane

“ OSMOSIS IN ANIMAL AND PLANT CELL AND THE TYPES OF SOLUTION”

Turgor Pressure – the pressure that tends to force water molecules out of the cell.

Diffusion Pressure – the force or pressure that causes water molecules to diffuse into the cell.

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THREE TYPES OF SOLUTION DURING OSMOSIS

1. Isotonic Solution – a solution whose osmotic pressure is equal top at of the cell, no change will occur thus a balance is maintained (equilibrium).

2. Hypertonic Solution- a solution whose osmotic pressure is greater than that of the cell.

- It will cause water to leave the cell, thus the cell will shrink or crenate.

3 Ways of Traversing the Cell Membrane

3. Hypotonic Solution – a solution whose osmotic pressure is lower than that of the cell

- It will cause water to enter the cell, thus the cell will swell or hemolyze or even burst in animal cell.

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“ Diffusion Through Channels”The diffusion of ions could be allowed

at all times or they may need signals to open or close

* Chemically- Gated Ion Channels- When a signalling molecule binds to

specific binding site on the transmembrane protein

* Voltage- Gated Ion Channels- When the ionic charge across a plasma membrane changes

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III. CARRIER-MEDIATED TRANSPORT

Carriers or Transporters- these are special transmembrane proteins that enable solute molecules to cross the phospholipid bilayer- They are usually quite specific, recognizing and transporting only a limited group of chemical substances or perhaps even a single substance.

3 Ways of Traversing the Cell Membrane

“FACILITATED DIFFUSION”A transporter assists a molecule to

diffuse through the membrane that it cannot otherwise penetrate

- Sponsors movement only in a “downhill” movement, along a concentration gradient where no metabolic energy is required

- Example is the transport of GLUCOSE (blood sugar) in cells

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III. ENDOCYTOSISThe ingestion of material by cells,

they are pathways for specifically internalizing solid particles, small molecules and ions, and macromolecules, requires energy.

Examples are the following:1. Phagocytosis- “cell eating”- A common method among protozoa,

lower metazoan and white blood cells

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- Digestion via lysosomal enzymes once a phagosome detaches

2. Pinocytosis- small areas of the surface membrane are invaginated in cells to form tiny vesicles (aveolae)- For the intake of vitamins,and similar

mechanisms may be important in translocating substances from one side of the cell to the other and internalizing signal molecules

- Examples are hormones

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3. Receptor-Mediated EndocytosisBring large molecules within the cellA ligand (particular molecule) binds to

the plasma membrane.Invaginations covered with the

protein clathrin are created (clathrin-coated pits)

Invaginations uncoats, the receptor and the ligand separates

Lysosome attacks the remaining vesicle, the endosome

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Contents are digested and absorbed in the cytoplasm

EXOCYTOSISExtruding contents to the surrounding

medium Removal of undigestible residues of

substances brought in by endocytosis, to secrete substances such as hormones and to transport a substance completely across a cellular

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barrier ( TRANSCYTOSIS)Actin and actin- binding proteins are

essential cytoskeletal components in the process of endocytosis and exocytosis.