CELL STRUCTURE & FUNCTION

Cell Theory

• All living things are made up of cells. • Cells are the smallest working units of all

living things. • All cells come from preexisting cells

through cell division.

Definition of Cell

A cell is the smallest unit that is capable of performing life functions.

Two Types of Cells

1. Prokaryotic2. Eukaryotic

Prokaryotic cell• Do not have internal structures surrounded

by membranes• Few internal structures• One-celled organisms, Bacteria

Eukaryotic cells• Contain organelles surrounded by membranes• Most living organisms

Eukaryotic cells

Organelle• a structure in a cell with a specific function

• Adult humans have around 100 trillion cells in the body

There are different types of cells :

Cells of epithelium – epithelial cells Cells of bones – osteocytesCells of cartilages – chondrocytesCells of muscle – muscle cellsCells of nervous tissue – Nerve cells or neuronsCells of connective tissue – fibroblast cellsCells of blood – leucocyte, erytrocyte

Plasma membrane• Also known as cell membrane or plasmalemma• Outer covering of cell• It separates the cell from the extracelluar space and

fluid• It is made up of phospholipid and protein

molecules double layer• Functions as a selective barrier that regulates the

passage of certain materials into and out of the cell• Fascilitates the transport of specific molecules

Double layer structure

• Some cells present the extension of cell membrane – microvilli, cilia and flagellum• Microvilli – seen in the cells lining intestine• Cilia – seen in the cells lining the trachea• Flagellum – long projection, seen in the sperms

sperm

Flagellum and cillia

Help cell move

Flagellum and cillia

Help cell move

Cytoplasm

• Cytoplasm refers to the jelly-like material with organelles in it & Surrounded by cell membrane

• Contains cell organelles like mitochondria, golgi apparatus, endoplasmic reticulum, ribosomes, lysosomes, centrioles and microtubules

• If the organelles were removed, the soluble part that would be left is called the cytosol. It consists mainly of water with dissolved substances such as amino acids in it.

Nucleus• Is the administrative center of the cell • Largest organelle• First described by Robert Brown in 1831• Stores the cell's hereditary material – DNA• Coordinates the cell's activities like growth, metabolism,

protein synthesis, and reproduction (cell division)• Generally there is only one nucleus per cell, but there are

exceptions (muscle cell)• The semifluid matrix found inside the nucleus is called

nucleoplasm• The nucleus contains – nucleolus and chromatin

Nuclear Membrane• Surrounds nucleus• Made of two layers• Openings allow material

to enter and leave nucleus

• The envelope is perforated with tiny holes called nuclear pores

• These pores regulate the passage of molecules between the nucleus and cytoplasm

Kromosom • Di dalam nukleus terdapat benang-benang halus yang disebut

kromatin. • Pada saat sel akan mulai membelah diri, kromatin menebal,

memendek membentuk kromosom. • Kromosom adalah struktur padat yang terdiri dari dua

komponen molekul, yaitu DNA dan protein.• Molekul DNA akan berikatan dengan protein histon dan

nonhiston membentuk sejumlah nukleosom.• Unit-unit nukleosom bergabung memadat membentuk

benang yang lebih padat dan terpilin menjadi lipatan-lipatan solenoid.

• Lipatan solenoid tersusun padat menjadi benang-benang kromatin.

Nucleolus

• Inside nucleus• Contains RNA to build proteins • A membrane-less organelle within the

nucleus• Under microscope it looks like a large dark

spot within the nucleus• A nucleus may contain up to four nucleoli

Mitochondria• Rod-shaped organelles that can be considered the power

generators of the cell • Produces energy (ATP) through chemical reactions –

breaking down fats & carbohydrate

• Contain outer and inner membranes

• Inner membrane is thrown into folds called cristae

• Cristae divide the interior into compartments

Endoplasmic Reticulum• Is a network of tubules• Synthesizes proteins, carbohydrates and lipids• Also involved in the storage and transport of

these structures• Two type of endoplasmic reticulum -

• Rough and smooth endoplasmic reticulum

Rough endoplasmic reticulum:• Rough because it contains ribosomes• Protein is synthesized here

Smooth endoplasmic reticulum:• Without ribosomes• Involved in carbohydrate and lipid

metabolism

Ribosomes

• Organelles that help in the synthesis of proteins. Ribosomes are made up of two parts, called subunits. 

• They get their names from their size. One unit is larger than than the other so they are called large and small subunits

• Both these subunits are necessary for protein synthesis in the cell. When the two units are docked together with a special information unit called messenger RNA, they make proteins. 

• Two types of ribosomes :• Free ribosomes – scattered in the cytoplasm• Fixed ribosomes – attached to the endoplasmic reticulum

• While attached to the ER, ribosomes make proteins that the cell needs and also ones to be exported from the cell for work elsewhere in the body

Golgi apparatus (Golgi complex)

• Consists of a stack of flattened membrane discs called cisternae

• Number of cisternae vary from 3 to 10

• Usually located close to the cell nucleus

• Protein 'packaging plant’

• It is the distribution and shipping department for the cell's chemical products

• It modifies proteins and lipids (fats) that have been built in the endoplasmic reticulum and prepares them for export outside of the cell or for transport to other locations in the cell

• In the cell, shipping and sorting done by the Golgi complex. It is a very important step in protein synthesis.

• If the Golgi complex makes a mistake in shipping the proteins to the right address, certain functions in the cell may stop. 

RE and Golgi apparatus

Lysosome• Contains digestive

enzymes for break up old cell components and bacteria

• Transports undigested material to cell membrane for removal

• Cell breaks down if lysosome explodes

Centrioles

• Animal cell contains pair of centrioles

• They are cylindrical structures, made up of short microtubules

• Each centriole contains 9 groups of microtubules

• Lead cromosomes movement during cell division

• Control flagella and cilia vibration