1. Cell Structure By Idura Namira

2. Learning Objectives

3. Units To Memorize

4. Resolution and Magnification Magnification is the number of times larger an image is compared with the real size of the object. Resolution is defined as the ability to distinguish between two separate points. – Resolution of a light microscope is 200nm. – Resolution of an electron microscope is 0.5nm. The general rule is that the limit of resolution is about one half the wavelength of the radiation used to view the specimen. This can be explained by the picture below.

5. Organelles Function OrganellesCharacteristicsFunctions Nucleus - Nuclear Envelope -Nuclear pores -Chromatin - Nucleolus Largest cell organelle Surrounded by two membranes known as the nuclear envelope. The outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum The nuclear envelope has many small pores called nuclear pores. The chromosomes are in a loosely coiled state known as chromatin. Nuclear pores allow and control exchange between nucleus and the cytoplasm. Substances leaving the nucleus through the pores are mRNA and ribosomes for protein synthesis. Substances entering through the nuclear pores are proteins to help make ribosomes, nucleotides, ATP and some hormones. Chromosomes contains DNA, which is organized into functional units called genes, genes control the activities of the cell and inheritance. Nucleolus makes ribosomes, using the information in it’s own DNA.

6. OrganellesCharacteristicsFunction Endoplasmic reticulum -rough ER - Smooth ER Extensive system of membranes running through the cytoplasm. Continuous with the outer membrane of the nuclear envelope. Rough ER is covered with so many tiny organelles called ribosomes. To transport proteins Smooth ER has a different function than the rough ER, make lipids and steroids, such as cholesterol, as well as reproductive hormones such as estrogen and testosterone. Ribosomes Found on the cytoplasm as well as on the rough ER. Very small, only about 25nm in size Made of RNA and protein Site of protein synthesis.

7. OrganellesCharacteristicsFunction Golgi Apparatus Collects, processes and sorts molecules (particularly protein from rough ER), ready for transport in Golgi vesicle either to other parts of the cell or out of the cell (secretion). In plants, enzymes in Golgi apparatus converts sugars into cell wall components. Golgi vesicle are used to make lysosomes. LysosomesSpherical sacs surrounded by a single membrane with and having no internal structure. Commonly 0.1-0.5 um in diameter. Contains digestive (hydrolytic) enzymes which must be kept separate from the rest of the cell to prevent damage. Responsible for the breakdown (digestion) of unwanted structures such as old organelles or even whole cells. Example : in mammary gland after lactation. In white blood cell, used to digest bacteria. Head of sperm contains lysosomes (acrosome) for digesting a path to the ovum.

8. OrganellesCharacteristicsFunction Mitochondria Usually about 1um in diameter. Can be in various shapes, but often sausage shaped. Surrounded by two membrane (an envelope) Inner one is called cristae which is folded to form finger like cristae. It projects into the interior solution (matrix) Site of aerobic cell respiration They make ATP Involved in the synthesis of lipids Contains ribosomes with size of 70S Contains small circular DNA molecules, also like those found in bacteria. DNA and ribosomes of mitochondria are still active and responsible for the coding and synthesis of certain vital proteins. Used to be a bacteria but can now no longer live independently. Part of the endosymbiosis theory. Cell Surface Membrane extremely thin, about 7nm Has three layers, described as a trilaminar appearance Partially permeable Controls exchange between the cell and its environment

9. OrganellesCharacteristicsFunction Microvilli Finger-like extensions of the cell surface membrane. Commonly found in epithelial cells (cells covering surfaces of structures) Greatly increase the surface area of the cell surface membrane. Useful for absorption Centrioles A cell has two centrioles A hollow cylinder about 0.4um long, formed from a ring of short microtubules, tiny tubes made of a protein called tubulin The microtubules are used as a starting point for growing the spindle microtubules for nuclear division.

11. Prokaryotes Vs Eukaryotes

13. Organelles That Are Not Present in Prokaryotes Nucleus Lysosomes Microtubules Endoplasmic Reticulum Mitochondria Golgi Apparatus

14. Tissues and Organs Usually, specialized cells show division of labor by being grouped into tissues; the tissues may be further grouped into organs and the organs into systems. – Tissues : A tissue is a collection of cells, together with any intercellular secretion produced by them, that is specialised to perform one or more particular functions. – Organ: part of the body which forms a structural and functional unit and is composed of more than one tissue – System: Collection of organs with a particular function.