The structure and function of Cell components M. Amin Tabatabaiefar, Ph.D Dep. Of Genetics and...

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The structure and function of Cell components

M. Amin Tabatabaiefar, Ph.DDep. Of Genetics and Molecular BiologyIsfahan University of Medical Sciences

Cells

• Smallest living unit• Most are microscopic

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Discovery of Cells

• Robert Hooke (mid-1600s)– Observed sliver of cork– Saw “row of empty boxes”– Coined the term cell

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Cell theory

• (1839)Theodor Schwann & Matthias Schleiden

“ all living things are made of cells”

• (50 yrs. later) Rudolf Virchow

“all cells come from cells”

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Principles of Cell Theory

• All living things are made of cells

• Smallest living unit of structure and function of all organisms is the cell

• All cells arise from preexisting cells

(this principle discarded the idea of

spontaneous generation)

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Cell Size

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Cells Have Large Surface Area-to-Volume Ratio

Characteristics of All Cells

• A surrounding membrane• Protoplasm – cell contents in thick fluid• Organelles – structures for cell function• Control center with DNA

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Cells chemical composition

• Chemical composition-by weight – 70% water– 7% small molecules

• salts• Fatty acids• amino acids• nucleotides

– 23% macromolecules

• Proteins• Polysaccharides• Lipids• DNA,RNA

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Cells chemical composition

• Chemical composition-by weight – 70% water– 7% small molecules

• salts• Fatty acids• amino acids• nucleotides

– 23% macromolecules

• Proteins• Polysaccharides• Lipids• DNA,RNA

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Prokaryotes and Eukaryotes, continued

Prokaryotes Eukaryotes

Single cell Single or multi cell

No nucleus Nucleus

No organelles Organelles

One piece of circular DNA Chromosomes

No mRNA post transcriptional modification

Exons/Introns splicing

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Prokaryotic and Eukaryotic CellsChromosomal differences

Prokaryotes The genome of E.coli contains

amount of 4X106 base pairs > 90% of DNA encode protein

Lacks a membrane-bound nucleus. Circular DNA and supercoiled domain

Histones are unknown

Eukaryotes The genome of yeast cells

contains 1.35x107 base pairs A small fraction of the total DNA

encodes protein. Many repeats of non-coding

sequences All chromosomes are contained

in a membrane bound nucleus DNA is divided between two or

more chromosomes A set of five histones

DNA packaging and gene expression regulation

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Section 7-2

Figure 7-5 Plant and Animal Cells

Go to Section:

Animal Cell

NucleusNucleolus

Rough Endoplasmic Reticulum

Smooth Endoplasmic Reticulum

Ribosomes

Golgi Bodies

Cell Membrane

Cytoplasm

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Representative Animal Cell

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• Now let’s talk about structures only found in PLANT Cells!!

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Representative Plant Cell

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Section 7-2

Figure 7-5 Plant and Animal Cells

Go to Section:

Plant Cell

Cell Membrane

Vacuole

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Plant Cell

Cell Membrane

Vacuole

Chloroplasts

Cell Wall

Nucleolus

Nucleus

Rough ER

Smooth ER

Golgi Bodies

Mitochondria

Ribosomes

Cytoplasm

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Organelles

• Cellular machinery • Two general kinds

– Derived from membranes– Bacteria-like organelles

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Cytoplasm

• Is a gel-like matrix of water, enzymes, nutrients, wastes, and gases and contains cell structures (organelles).

• Fluid around the organelles called cytosol.

• Most of the cells metabolic reactions occur in the cytoplasm.

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Cytoplasm• Viscous fluid containing organelles• components of cytoplasm

– Interconnected filaments & fibers – Fluid = cytosol– Organelles (not nucleus)– storage substances

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Cytoskeleton

Cytoskeleton

• Function– structural support

• maintains shape of cell• provides anchorage for organelles

– motility• cell locomotion• cilia, flagella, etc.

– regulation • organizes structures &

activities of cell

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Cytoskeleton• Made of three types of

filaments• Acts as skeleton and

muscle• Provides shape and

structure• Helps move organelles

around the cell

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Cytoskeleton

• Give the cell its shape• Supports the organelles inside the cell• Provides “tracks” for movement inside the

cell• Is involved in cell division

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Function

• Cytoskeletons maintain cell shape, protects the cell, enables cellular motion (using flagella), and plays important roles in both intercellular transport and cellular division.

Cytoskeleton• Filaments & fibers

• Made of 3 fiber types– Microfilaments– Microtubules– Intermediate filaments

• 3 functions:– mechanical support– anchor organelles– help move

substances

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Components of cytoskeleton: 1) Microfilaments

• Solid rods of globular proteins.

• Important component of cytoskeleton which offers support to cell structure.

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Components of cytoskeleton: 2) Microtubules

Centrosomes and Centrioles

• The centrosome– Is considered to be a “microtubule-organizing

center”– Contains a pair of centrioles

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Centrioles

• Found only in animal cells.

• Self-replicating• Made of bundles of

microtubules.• Help in organizing cell

division.

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• Microtubules– Shape the cell– Guide movement of organelles– Help separate the chromosome copies in

dividing cells

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Cilia and Flagella

• External appendages from the cell membrane that aid in locomotion of the cell.

• Cilia also help to move substance past the membrane.

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An overview of cytoskeleton• Three major cytoskeletal systems and their general properties

• a) Intermediate Filaments - a system of elastic fibers - used to strengthen cells and to transmit mechanical strain across cells in a tissue. These filaments are purely skeletal in nature.

• b) Microtubules - rigid protein tubules. These are involved in generation of cell shape and provide substrate for two different types of motor systems, dyneins and kinesins. The mitotic spindle is a variant form of the microtubular cytoskeleton.

• c) Microfilaments (actin filaments) - this is the most complex system. Occurs in many forms, bundles of fibers or networks. Interacts with many types of molecules including its own class of motor proteins, the myosins. Its most elaborate form occurs in striated muscle. Microfilaments are responsible for cytoplasmic streaming and amoeboid motion.

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A = actin, IF = intermediate filament, MT = microtubule

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• cilia are thread-like projections of certain cells that beat in a regular fashion to create currents that sweep materials along;

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Flagella may extend to the rear of a cell and push it forward by snakelike wriggling, or stick out in front and draw it along.

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Cilia & Flagella Structure

• Bundles of microtubules• With plasma membrane

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Centrioles

• Pairs of microtubular structures• Play a role in cell division

Intercellular junctions

• Plant cells– plasmodesmata

• channels allowing cytosol to pass between cells

plasmodesmata

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Cell membrane

• Found in ALL Cells

• Structure– double layer of fat

• phospholipid bilayer– receptor molecules

• proteins that receive signals

lipid “tail”

phosphate“head”

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• Function– separates cell from outside– controls what enters or leaves cell

• O2, CO2, H2O, nutrients, waste– recognizes signals from other cells

• allows communication between cells

Cell membrane

lipid “tail”

phosphate“head”

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Phospholipids

• Phosphate heads: Hydrophilic (love water)

• Lipid tails: Hydrophobic (fear water)lipid “tail”

phosphate“head”

Water Outside the cell

Water Inside the cell

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Animal cell surface

• Extracellular matrix– collagen fibers in network of glycoproteins

• support• adhesion• movement• regulation

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Intercellular junctions in animals

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Intercellular junctions in animal cells

– tight junctions• membranes of adjacent cells fused forming barrier

between cells• forces material through cell membrane

– gap junctions• communicating junctions• allow cytoplasmic movement between adjacent cells

– desmosomes• anchoring junctions• fasten cells together in strong sheets

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Cell Wall Differences

• Plants – mostly cellulose• Fungi – contain chitin

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Functions of the Cell Wall

• Maintaining and determining cell shape• Physical barrier to many things like

pathogens• Prevents the membrane from bursting in a

hypotonic medium• It can control rate and direction of cell

growth• Metabolic role- the wall has some

enzymes for moving and secretion

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Membranous Organelles

• Functional components within cytoplasm• Bound by membranes

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Endoplasmic Reticulum

• Helps move substances within cells

• Network of interconnected membranes

• Two types– Rough endoplasmic reticulum– Smooth endoplasmic reticulum

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• Network of continuous sacs, studded with ribosomes.

• Manufactures, pro-cesses, and transports proteins for export from cell (vesicles)

• Continuous with nuclear envelope.

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• Ribosomes attached to surface– Manufacture protiens– Not all ribosomes attached to rough ER

• May modify proteins from ribosomes

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Ribosomes• Are the sites of protein synthesis.

• Found attached to the Rough endoplasmic reticulum or free in the cytoplasm.

• 60% RNA and 40% protein.

• Protein released from the ER are not mature, need further processing in Golgi complex before they are able to perform their function within or outside the cell.

55Courtesy of http://micro.magnet.fsu.edu/

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Structure

• Non-membrane bounded particles in cells• Made in the nucleolus• The number of ribosomes in a cell

depends on the cell’s function• Consist of 2 subunits

– 60S (large)– 40S (small)– Each subunit has its own mix of ribosomal

RNA (rRNA) and proteins

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• Similar in appearance to rough ER, but without the ribosomes.

• Involved in the production of lipids, carbohydrate metabolism, and detoxification of drugs and poisons.

• Stores calcium.

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• No attached ribosomes• Has enzymes that help build molecules

– Carbohydrates– Lipids

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Function

• The major function is the synthesis of lipids & carbohydrates (such as phospholipids & steriods)

• The function is dependent of the cell: testes: produces testosterone liver:helps detox the body off of drugs by producing enzymes muscles: assists in the contraction of muscle cells & in brain cells Works with rough ER to transport molecules to other parts of the cell.

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Golgi apparatus

• Golgi apparatus are found in both animal and plant cells.

• Their structure is made up of flat membranes by the name of cisternae as many as 60 have been found in a single cell.

• Consists of four sections cis-Golgi network, medial-Golgi, endo-Golgi, and trans-Golgi all of which carry different ensymes that help them get there job done.

• Located next to the cell nuclus most of the time.

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Golgi Apparatus

• Involved in synthesis of plant cell wall• Packaging & shipping station of cell

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Golgi complex- It is organelle in the cell that is responsible for sorting and correctly shipping the proteins produced in the ER. Just like our postal packages which should have a correct shipping address, the proteins produced in the ER, should be correctly sent to their respective address.

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.

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Functions

• The functions of the Golgi apparatus is to modify proteins, transport lipids through out the cell and create lysosomes( garbage disposal of cell).

• The golgi gets everything ready to be sent out to its proper place for the cells survival

64Courtesy of: http://micro.magnet.fsu.edu

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Protein modifications in Golgi [Fig. 12-6 from

Becker]

Predict the location of enzymes, galactosyl transferase andsialic acid transferase

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Golgi Apparatus Function

1. Molecules come in vesicles

2. Vesicles fuse with Golgi membrane

3. Molecules may be modified by Golgi

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Lysosomes

• Contain digestive enzymes• Functions

– Aid in cell renewal– Break down old cell parts – Digests invaders

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Contain digestive enzymes that break down wastes and old organelles

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Lysosomes function as the cell's recycling compartment.

Lysosomes receive cellular and endocytosed proteins and lipids that need digesting. The metabolites that result are transported either by vesicles or directly

across the membrane.

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Vacuoles

• Membrane bound storage sacs• More common in plants than animals• Contents, Store waste or raw materials used

in synthesis of proteins

– Water– Food– wastes

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Function• The function and importance of vacuoles vary according to the type

of cell, having much greater importance in plant cells than in animal and bacteria cells. In plant cells it is responsible for maintaining the shape and structure of the cell. The pressure applied by the vacuole, called turgor, is what controls the size of the cell not the expanding cytoplasm. In animal cells, vacuoles are generally small.

In general the functions of vacuoles include:– Removing harmful material from the cell– Containing waste products– Maintaining turgor within the cell– Maintaining an internal acidic pH– Store nutrients and metabolites

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Bacteria-Like Organelles

• Release & store energy

• Types – Mitochondria

(release energy) – Chloroplasts

(store energy)

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Mitochondria

• Have their own DNA• Bound by double membrane

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Mitochondria

• Provides the cell with energy.

• Is the site of cellular respiration.

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MitochondriaMitochondria are membrane-enclosed organelles distributed through

the cytosol of most eukaryotic cells. Their main function is the conversion of the potential energy of food molecules into ATP.

Every type of cell has a different amount of mitochondria. There are more mitochondria in cells that have to perform lots of work, for example- your leg muscle cells, heart muscle cells etc. Other cells need less energy to do their work and have less mitochondria.

http://users.erols.com/jkimball.ma.ultranet/BiologyPages/O/O.html

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Mitochondria

• Break down fuel molecules (cellular respiration)

– Glucose– Fatty acids

• Release energy– ATP

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14_10_resp_enzy_comp.jpgElectron transport and H+ pumping in mitochondria

4 4 2

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Chloroplasts

• Derived form photosynthetic bacteria• Solar energy capturing organelle

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Photosynthesis

• Takes place in the chloroplast• Makes cellular food – glucose

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Review of Eukaryotic Cells

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Review of Eukaryotic Cells

The structure and function of Cell components M. Amin Tabatabaiefar, Ph.D Dep. Of Genetics and...

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