Cells & Organelles

Lecture 1

Cells & Organelles Biology, Campbell & Reece 7th Edn. Ch 1, pp. 1-8; Ch 6, pp. 94-118; Ch 27, pp. 534-538

By

Dr Mohamed Abumaree Molecular Reproductive Biology & Immunology College of Medicine King Saud bin Abdulaziz University for Health Science Riyadh 2009

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Objectives 1.To understand the difference between pro- & eukaryotic cells 2.To

identify

the

organelles

found

in

eukaryotic cells & know their functions 2

What is Biology?  A science that study life to understand: 1. The development of living organisms from a single microscopic cell! 2. The formation of energy! 3. How human mind works! 4. The improvement of the quality of life, for example, human disease identification by genetics & cell biology 3

 Organisms: living things  Organs: Such as brain, heart, kidney  Organ systems: a number of organs with a specific function, such as the digestive system, system (tongue, stomach & intestines)  Tissues: A group of similar cells aggregated & associated together to perform one or more specific functions in the body  Four basic tissue types: Muscle; Nerve; Epidermal & connective tissues 4

What Are Cells? 5

 Cells: Structural & functional units of all living organisms  Unicellular organisms (bacteria): consist of a single cell  Multicellular organisms (humans): many cells of many kinds, such as muscle cells which are organized into various specialized tissues  Cells perform all activities of life, such as cell division to form new cells Cell division

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 Cell division: essential for reproduction, growth & repair  Cell contains chromosomes (partly made of deoxyribonucleic acid, DNA)  DNA is the substance of genes  Genes: inheritance units transmit information from parents to offspring  Chromosome has one very long DNA molecule, with many genes arranged along its length 7

The Heritable Information

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The DNA of chromosomes replicates as a cell prepares to divide Thus, each of the two cellular offspring inherits a complete set of genes

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 DNA molecule is made up of two long chains (double helix) 

DNA chains are linked by four nucleotides (chemical building blocks)  Nucleotides encode the information in genes, which encoding proteins

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 DNA provides the design of inheritance, inheritance but proteins build up & maintain the cell  We utilize the same genetic code  Nucleotide sequences determine the similarities or differences between organisms  Genome: the entire library of genetic instructions  Within the genome, genes coding for different proteins with specific functions 11

How Can we Study Cells?

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 Microscope (morphology & structure) has 2 important parameters: 1. Magnification 2. Resolution  Light microscopes (magnify to ~1,000 times the size of the actual specimen  Electron microscope (magnify a hundredfold over the light microscope)  Cell fractionation (composition & function) to separate organelles from each other by a centrifuge (size & density) 13

Forms of Cells 14

PROKARYOTIC CELLS microorganisms, such as bacteria

EUKARYOTIC CELLS plants & animals 15

 Eukaryotic cells bigger than prokaryotic cells  In eukaryotic cells, chromosomes located in nucleus  In prokaryotic cells, chromosomes concentrated in nucleoid  In eukaryotic cells, nucleus surrounded by a membrane (nuclear envelope)  In prokaryotic cells, there is no membrane surrounding the nucleoid 16

 Cells are surrounded by a plasma membrane, membrane a barrier allows the passage of oxygen, nutrients & wastes to service the cell  Eukaryotic cells also have an internal membranes  The region between nucleus & plasma membrane is the cytoplasm, cytoplasm a semifluid substance (Cytosol)  Eukaryotic cells contains membrane-bounded organelles in their cytoplasm unlike prokaryotes 17

Membranes consist of a double layer of phospholipids & other lipids Embedded in the lipid bilayer or attached to its surfaces diverse proteins or carbohydrates

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Animal Cell Structure 19

NUCLEUS  Most prominent organelle in animal cell  Nuclear envelope encloses the nucleus  Nuclear envelope punctured by pores to regulate the passage of large macromolecules  Nuclear envelope lined by nuclear lamina, lamina mechanically supports nuclear envelope to maintain nucleus shape 20

 Nucleus contains chromosomes, chromosomes made up of chromatin, a complex of proteins & DNA  Human cell has 46 chromosomes  Sex cells (egg & sperm) have only 23 chromosomes  Nucleolus: prominent structure in nondividing nucleus  Nucleus directs protein synthesis as instructed by the DNA 21

Cytoplasm 1. Cytoplasm: entire region between nucleus & plasma membrane 2.Most of metabolic activities occur in the cytoplasm 3. Contains many organelles suspended in a semifluid medium (cytosol) 22

Ribosomes 1.Ribosomes perform protein synthesis 2.Made of ribosomal RNA & protein 3.Two types with identical structures synthesizing proteins with different functions  Free ribosomes (suspended in the cytosol)  Bound ribosomes (attached to the outside of ER or nuclear envelope) 23

The endomembrane system  Membranes with different structure & function: 1. 2. 3. 4. 5. 6.

Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Various kind of vacuole Plasma membrane

 Function: 1. 2. 3. 4.

Protein synthesis Protein transport into membranes/organelles/out of the cell Lipid metabolism & movement Poisons detoxification 24

The Endoplasmic Reticulum 1. Smooth ER (outer surface lacks ribosomes)  Functions in lipid synthesis; carbohydrate metabolism; drug & poisons detoxification; calcium storage

2. Rough ER (ribosomes, so appears rough)  Making secretory glycoproteins..)

protein

(such

as

insulin,

 Addition of membrane proteins & phospholipids to its own membrane 25

Golgi Apparatus  Manufacturing center (such as polysaccharides), warehousing, sorting & shipping products of ER to other destinations

Lysosomes  Contain hydrolytic enzymes (specialized proteins speed up chemical reactions in cells) that digest all kinds of macromolecules 26

Mitochondria 1.Found in eukaryotic cells (plants, animals, fungi, & protists) 2.Cells have a single large mitochondrion or many of mitochondria 3.Contains enzymes, DNA & ribosomes; so involved in metabolic activity such as ATP (Adenosine-triphosphate ) production 27

Chloroplasts  Contain green pigment chlorophyll, enzymes, DNA, ribosomes  Function in the photosynthetic production of sugar  Found in leaves & other green organs of plants & in algae 28

Peroxisomes 1. Produce H2O2 2. Break fatty acids to produce energy 3. Detoxify harmful compounds (alcohol) in liver 4. Convert H2O2 (TOXIC) to H2O

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Cytoskeleton  A network of fibers including: 1. Microtubules 2. Microfilaments 3. Intermediate filaments

 Functions 1. Mechanically supporting the cell shape 2. Cell motility (movement) 3. Regulate the biochemical activities in the cell 30

Cilia and Flagella  Attachment sticking out from some cells  Enhance cell movement (Human sperm)  Move fluid over the tissue surface  For example, in woman’s reproductive tract, tract cilia lining the oviduct (fallopian tubes) help move an egg toward the uterus

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Bacteria are microscopic & unicellular

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 Different shapes (spheres “cocci”, rods “bacilli” & spirals)  Smaller than eukaryotic cells  Cell wall protects from bursting in a hypotonic environment  Cell wall is covered by a capsule (a sticky layer) for adherences & protection from attacks by other prokaryotes  Dominate the biosphere 33

 Adapt, reproduce and live in diverse places (acidic, salty, cold or too hot)  The internal structure & genome are simpler than eukaryotes  Genome: 1. Has ~1000 as much DNA 2. Consist of a ring of DNA (Single chromosome) that is associated with few proteins 3. Chromosome located in a nucleoid region 34

A typical prokaryotic cell may also have much smaller rings of DNA called plasmids, most consisting of only a few genes

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