Cells

Levels of Organization

• Chemical (Least complex)

• Cellular

• Tissue

• Organ

• Organ System

• Organism (Most complex)

History• 1600’s Anton Van Leeuwenhoek - first to view

nature w/microscope• 1665 Robert Hooke - Coined term ‘cells’• 1838 Matthias Schleiden - ‘All plants are made of

cells’• 1839 Theodor Schwann - ‘All animals are made of

cells’• 1855 Rudolf Virchow - ‘All cells come from pre-

existing cells’

Cell Theory

• Schleiden and Schwann 1840.

• All living things are made of cells.

• New cells are produced from existing cells.

• Cells are the basic units of structure and function of all living things.

Two types of cells.

• Prokaryotic cells make up prokaryotes.• Eukaryotic cells make up eukaryotes.

• Prokaryotes: No nucleus, genetic material in cytoplasm, only organelle = ribosomes, smaller, simpler, unicellular evolutionarily more ancient

• Eukaryotes: Have nucleus, larger, more complex, more organelles, evolutionarily more modern.

Basic Cell Structures

• Most prokaryotes (bacteria) difficult to see with light microscope

• All cells have cell membrane, cytoplasm, genetic material and ribosomes

• Presence of other cells structures (organelles) varies

Describing Cell Structures

• Include:– Structure: describes the shape and smaller

component parts of the organelle

– Location: Nucleus, cytoplasm or cell membrane, sometimes more specific

– Function: what does it do and how does it do it

Cell Membrane

• Is a phospholipid bilayer with some proteins & carbohydrates associated with it.

• Integral proteins form channels & pumps to pass substances across the membrane.

• Represented by the “Fluid Mosaic Model”.

Cell Membrane Picture

Cell Membrane Functions

• Controls what goes in and out of the cell.

• Proteins are unique within species and individuals and therefore serves as a form of cellular identification.

• Encloses cell contents and separates from the extracellular space.

• Support & Protection?

Cytoplasm

• A watery gel in which all the organelles reside

• The site of multiple enzyme controlled chemical reactions.

• Polar compounds go into solution while non-polar compound remain suspended

Enzymatic Regulation of Cells

• Enzymes are biological catalysts.

• Enzymes are proteins

• Speed up the rate of chemical reactions

• Enzyme Action Effected By:– pH– Temperature– concentration

Cell Wall

• When present is exterior to the cell membrane.

• Made primarily of cellulose and provides significant support and protection to the cell.

• Not present in animal cells.

Cell Wall Picture

Nucleus

• Spherical shape which can be seen with an ordinary light microscope.

• Contains nucleolus & chromatin• Controls all cell functions by controlling

protein synthesis and hereditary blue-print.

• Surrounded by a nuclear envelope - a double membrane layer with pores.

Nucleus

• Nucleolus - a dense area where ribosome production begins.

• Contains DNA bound to histone proteins. The complex is called both chromatin and chromosomes depending on the stage of the cell cycle and the function it is performing.

Nucleus Picture

Organelles• “Little organs” including:• Ribosomes• Endoplasmic Reticulum• Golgi Apparatus• Lysosomes• Vacuoles• Chloroplasts• Mitochondria• Centrioles• Cytoskeleton

– (Microfilaments & Microtubules)

Ribosome Picture

Ribosomes

• Structure: “B” shape, smallest organelle, made of RNA & protein

• Location: Cytoplasm (Free) or surface of rough endoplasmic reticulum (Fixed)

• Function: AA joined on surface = site of protein synthesis

Ribosome S.L.F.

• Consisting of a large and small subunit.

• Made of rRNA and protein

• The smallest organelle.

• Can be attached to R.E.R or free.

• Site of protein assembly, AA chemically bonded together here (10 Structure)

Endoplasmic Reticulum (R.E.R. & S.E.R.) Pictures

Rough Endoplasmic Reticulum

• A flat & folded internal membrane maze

• In the cytoplasm usually close to the nucleus.

• Modifies & transports proteins.

• Assembles & transports cell membrane parts.

Smooth Endoplasmic Reticulum

• Does not have ribosomes attached.

Golgi Apparatus Picture

Golgi Apparatus S.L.F.

• Stacks of individual enclosed membranes wider than E.R.

• Located in the cytoplasm

• Assembles & packages lipoproteins

• Binds carbohydrates to proteins

Lysosomes Picture

Lysosomes S.L.F.

• Found in the cytoplasm

• Contains digestive enzymes

• Digests food particles

• Catabolism of waste & worn out cell parts

Vacuoles S.L.F.

• Various sac-like shapes in cytoplasm

• Large in plant cells

• Stores water, proteins, carbos, salts

• The term ‘vesicle’ is used for a vacuole with a transport function.

Vacuoles Picture

Chloroplast Picture

Chloroplast S.L.F.

• Contains maternal DNA, remnants of photosynthetic prokaryotic ancestors

• Found in plants of course but also in some protists.

• Captures the energy from sunlight to transform carbon dioxide and water into sugars and oxygen.

Mitochondrion Picture

Mitochondria

• Structure: Contains maternal DNA, Kidney shape, double folded inner membrane

• Location: Cytoplasm

• Function: Aerobic Cellular Respiration = Converts food energy into a form of energy (ATP) the cell can use.

• Special: Are remnants of aerobic prokaryotes as explained by the endosymbiotic theory

Centrisome Picture

Centrisome S.L.F.

• Term centrisome refers to a set of two centrioles in a cell.

• 2 centrioles arranged at 900 angles to each other, made of microtubules in a cylindrical shape grouped in 9 bunches of 3.

• Aids in cell division as part of the mitotic spindle.

• Only present in animal cells.

Cytoskeleton Microtubules Microfilaments

• Long hollow structures found at the base of cilia & flagella and acts as a rigid lever like bone aiding cilia & flagella movement. Serves to maintain cell shape as well as be a track for transport of organelles.

• Found in the cytoplasm and made of actin & myosin proteins.Contractile ability. Part of cleavage furrow. When attached to microtubules causes movement of cilia & flagella.

Cytoskeleton Microtubules & Microfilaments

Pictures

Microtubules

• Structure: long, slender, made of tubulin proteins with 2 in the middle surrounded by 9.

• Location: throughout cytoplasm, also at base of cilia and flagella

• Function: part of mitotic spindle,involved in movement of cilia & flagella, transport track

Microfilaments• Structure: long, slender, made of actin

and myosin proteins

• Location: cytoplasm & base of cilia & flagella

• Function: contracts like muscle so aids in the movement of cilia, flagella and cell division by forming a cleavage furrow, structure and support of the cell

Other

• Flagella - in humans only found in sperm

• Barr body - the second X chromosome in females only which is inactivated

Cilia PictureCilia

Flagella Picture

Flagella

Cilia & Flagella Structure

Eukaryotic Cilia S.L.F.

• Structure - 2 to 20um long, 9 double microtubules around 2, usually many in one cell, .25um diameter

• Location – protruding from cell, but covered by plasma membrane

• Function – locomotion or movement of liquids or particles in fixed cells, signal antenna

Eukaryotic Flagella S.L.F.

• Structure – same as cilia except only 1 or 2 per cell if present, but longer (10 to 200um)

• Location – protruding from cell, but covered by plasma membrane

• Function – locomotion

The Cell as a Factory• Cell Membrane - gate security• Nucleus - C.E.O. office

– Chromosomes = secret recipe

• Cytoskeleton - building supports• Vacuoles (Vesicles) - raw material storage

and distribution • Ribosomes - assembly line machinery• Lysosomes - waste removal system &

cleanup• Mitochondrion - main power source• Chloroplasts - power source in ‘green’ plants• ER - product modification and transport• Golgi - product packaging

Part 2

Movement Across the Cell Membrane

• The cell membrane is a selectively - permeable (semi-permeable) membrane.

• Many large molecules cannot cross.

• Many charged molecules cannot cross.

• Some non-lipid soluble molecules cannot cross.

Movement Across the Cell Membrane

• Active Transport Mechanisms– Require energy (A.T.P.)– Move against a concentration gradient

• Passive Transport Mechanisms– Do not require energy– Moving with a concentration gradient

Movement Across the Cell Membrane

• Active Transport Mechanisms– Endocytosis

• Phagocytosis - cell eating or engulfing solids• Pinocytosis - cell drinking or engulfing liquid

– Exocytosis– Protein Pumps

• Passive Transport Mechanisms– Diffusion– Osmosis– Facilitated Diffusion

Movement Across the Cell Membrane

• Diffusion - driven by the movement of particles in a gas or liquid state from an area of higher concentration to an area of lower concentration

• Osmosis - diffusion of water across a semi-permeable membrane

• Facilitated Diffusion - movement of particles down the concentration gradient with the help of integral proteins in the cell membrane

Tonicity

• Isotonic - an equal concentration of solutes both in and outside a cell

• Hypertonic - a solution with a greater concentration of solutes in relation to another

• Hypotonic - a solution with a lower concentration of solutes in relation to another

Tonicity in Cells

• Hypertonic - term used when the extracellular solute concentration is greater than the cell resulting in movement of water out of the cell causing cell shrinkage or crenation

• Hypotonic - term used when the extracellular solute concentration is less than the cell resulting in movement of water into the cell causing cell swelling

Fluid Balance - Homeostasis

• All living things function best in a narrow range of conditions.

• Living things have mechanisms to maintain a stable internal environment

• Examples: temperature, pH, water content

• All living things need water

Water Balance

• In plants, water balance is often controlled by: stoma, waxy cuticle, shape, size

• In complex organisms like humans water balance is primarily influenced by water intake versus water loss but, there are several regulating mechanisms that control this balance.

Water Regulation

• Sweating, respiration, excretion = loss• Hypothalamus detects [H2O] in the blood.• Antidiuretic hormone (ADH) released and

kidneys decrease water removal from the blood & loss in urine.

• Thirst mechanism • Increased [H2O] in blood decreases [ADH]

and water removal from blood by kidneys increases again. (Negative Feedback Loop)

Specialized Cell Types

• Differentiated cells contribute to the function of the organism as a whole.

• Unicellular organisms must perform all the activities associated with life

• Multicellular organisms are more complex & interdependent because individual cells perform only specific functions for the good of the whole organism.

Examples of Specialized Cells

• Nerve Cells (Neurons) - carry messages in the form of an electrochemical signal

• Pancreas Cells - some secrete insulin and some secrete peptidase, amylase or lipase

• RBC - have hemoglobin to carry oxygen