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CELL STRUCTURE & FUNCTION
Cell TheoryAll 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 CellA cell is the smallest unit that is capable of performing life functions.
Two Types of CellsProkaryoticEukaryotic
Prokaryotic cellDo not have internal structures surrounded by membranesFew internal structuresOne-celled organisms, Bacteria
Eukaryotic cellsContain organelles surrounded by membranesMost living organisms
Organellea 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 membraneAlso known as cell membrane or plasmalemmaOuter covering of cellIt separates the cell from the extracelluar space and fluidIt is made up of phospholipid and protein molecules double layerFunctions as a selective barrier that regulates the passage of certain materials into and out of the cellFascilitates the transport of specific molecules
Double layer structure
Some cells present the extension of cell membrane microvilli, cilia and flagellumMicrovilli seen in the cells lining intestineCilia seen in the cells lining the tracheaFlagellum long projection, seen in the sperms
spermFlagellum and cilliaHelp cell move
Flagellum and cilliaHelp cell move
CytoplasmCytoplasm 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.
NucleusIs the administrative center of the cell Largest organelleFirst described by Robert Brown in 1831Stores the cell's hereditary material DNACoordinates 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 nucleoplasmThe nucleus contains nucleolus and chromatin
Nuclear MembraneSurrounds nucleusMade of two layersOpenings allow material to enter and leave nucleus The envelope is perforated with tiny holes called nuclear poresThese 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.
NucleolusInside nucleusContains RNA to build proteins A membrane-less organelle within the nucleusUnder microscope it looks like a large dark spot within the nucleusA nucleus may contain up to four nucleoli
MitochondriaRod-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 membranesInner membrane is thrown into folds called cristaeCristae divide the interior into compartments
Is a network of tubulesSynthesizes proteins, carbohydrates and lipidsAlso involved in the storage and transport of these structuresTwo type of endoplasmic reticulum - Rough and smooth endoplasmic reticulum
Rough endoplasmic reticulum:Rough because it contains ribosomesProtein is synthesized here
Smooth endoplasmic reticulum:Without ribosomesInvolved in carbohydrate and lipid metabolism
RibosomesOrganelles 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 cytoplasmFixed 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 cisternaeNumber of cisternae vary from 3 to 10Usually located close to the cell nucleus Protein 'packaging plant
It is the distribution and shipping department for the cell's chemical productsIt 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
LysosomeContains digestive enzymes for break up old cell components and bacteriaTransports undigested material to cell membrane for removalCell breaks down if lysosome explodes
CentriolesAnimal cell contains pair of centriolesThey are cylindrical structures, made up of short microtubulesEach centriole contains 9 groups of microtubulesLead cromosomes movement during cell divisionControl flagella and cilia vibration