Cell BiologyCell BiologyCELL STRUCTURECELL STRUCTURE

Levels of OrganizationLevels of Organization The levels of life are organized hierarchically:The levels of life are organized hierarchically:……from lowest to highest:from lowest to highest:

1. ATOMS1. ATOMSeg. carbon, oxygen atomseg. carbon, oxygen atoms

2. MOLECULES2. MOLECULESeg. glucose, proteins, neutral fats, cholesteroleg. glucose, proteins, neutral fats, cholesterol

3. ORGANELLES (structures that make up cells)3. ORGANELLES (structures that make up cells)eg. nucleus, mitochondria, endoplasmic reticulaeg. nucleus, mitochondria, endoplasmic reticula

4. CELLS4. CELLSeg. nerve cells, smooth muscle cellseg. nerve cells, smooth muscle cells

5. TISSUES (comprised of similar cells)5. TISSUES (comprised of similar cells)eg. nerve tissue, muscle tissue, epithelial tissue, connective eg. nerve tissue, muscle tissue, epithelial tissue, connective

tissuetissue

Nerve tissue – sense stimuli and transmit signals throughout animal.Nerve tissue – sense stimuli and transmit signals throughout animal.Muscle tissue – movement, support; three types:Muscle tissue – movement, support; three types:

i. Skeletal (Striated) – voluntary bodily movements;i. Skeletal (Striated) – voluntary bodily movements;ii. Smooth (Visceral) – involuntary contractions (blood vessels, intestine, ii. Smooth (Visceral) – involuntary contractions (blood vessels, intestine, bladder, etc);bladder, etc);iii. Cardiac (Heart) – pumping of heart.iii. Cardiac (Heart) – pumping of heart.

Epithelial tissue – Protects: covers outside of body, lines organs and cavities Epithelial tissue – Protects: covers outside of body, lines organs and cavities within body.within body.

Connective tissue – binds and supports other three tissue types; six types:Connective tissue – binds and supports other three tissue types; six types:i. Loose Connective tissue – most widespread; attaches epithelia to other i. Loose Connective tissue – most widespread; attaches epithelia to other tissues and holds organs in place tissues and holds organs in place strong and elastic in nature; strong and elastic in nature;ii. Dense Connective tissue – tendons (muscle-to-bone) and ligaments (bone-to-ii. Dense Connective tissue – tendons (muscle-to-bone) and ligaments (bone-to-bone);bone);iii. Bone – mineralized (Caiii. Bone – mineralized (Ca2+2+ & Mg & Mg2+2+) for support and protection;) for support and protection;iv. Cartilage – flexible support in certain areas (nose, ears, trachea, vertebrae);iv. Cartilage – flexible support in certain areas (nose, ears, trachea, vertebrae);v. Blood – ‘connects’ different parts of body by transporting materials;v. Blood – ‘connects’ different parts of body by transporting materials;vi. Fat (Adipose) tissue – pads and insulates body.vi. Fat (Adipose) tissue – pads and insulates body.

6. ORGANS (comprised of various tissue-types)6. ORGANS (comprised of various tissue-types)eg. heart, brain, liver.eg. heart, brain, liver.

7. ORGAN SYSTEMS (comprised of various organs)7. ORGAN SYSTEMS (comprised of various organs)eg. Nervous System, Digestive Systemeg. Nervous System, Digestive System

8. ORGANISM (comprised of organ systems)8. ORGANISM (comprised of organ systems)eg. human beings, cats, wildebeesteg. human beings, cats, wildebeest9. POPULATIONS/COMMUNITIES9. POPULATIONS/COMMUNITIES

Definition: CELL – the structural and functional unit of Definition: CELL – the structural and functional unit of life. It is the smallest structure capable of performing life. It is the smallest structure capable of performing all of the functions necessary for life.all of the functions necessary for life.

FUNCTIONS NECESSARY FOR LIFE:FUNCTIONS NECESSARY FOR LIFE:1. Reproduce ON OWN! (excludes viruses which 1. Reproduce ON OWN! (excludes viruses which require cells to repr.)require cells to repr.)2. Grow2. Grow3. Respire (Metabolize) – Cellular Respiration 3. Respire (Metabolize) – Cellular Respiration (mitochondria)(mitochondria)glucose (Cglucose (C66HH1212OO66) + O) + O22 CO CO22 + H + H22O + ATP energyO + ATP energy4. Contain genetic material (RNA and DNA)4. Contain genetic material (RNA and DNA)5. Respond to stimuli5. Respond to stimuli

Molecules Making Up CellsMolecules Making Up Cells1.1. Carbohydrates (energy, identification)Carbohydrates (energy, identification)2.2. Proteins (energy, digestion, structure, Proteins (energy, digestion, structure,

hormones etc)hormones etc)3.3. Lipids (incl. fats, steroids) – (energy, Lipids (incl. fats, steroids) – (energy,

insulation, hormones, cushioning)insulation, hormones, cushioning)4.4. Nucleic Acids (RNA/DNA) – (blueprint for Nucleic Acids (RNA/DNA) – (blueprint for

proteins)proteins)- All of these molecules are made up of atoms All of these molecules are made up of atoms

(elements); the main elements comprising (elements); the main elements comprising living organisms are: C, H, N, O.living organisms are: C, H, N, O.

- Organic = C and H.Organic = C and H.

Classifying CellsClassifying Cells CELLSCELLS

PROKARYOTIC EUKARYOTIC

-- smaller, less organized

-- lack a true nucleus

-- lack membrane-bound organelles

-- bacteria -- single circular chromo-some

-- have a true nucleus with a cell membrane

-- possess membrane-bound organelles

-- 10X size of prok. cells

-- focus of Biology 12

Eukaryotic Cells

Plant Cells Animal Cells

-- p. 51 Figure 3.3

-- possess a cell wall

-- have chloroplasts

-- large, contractile vacuole

-- p. 50 Figure 3.2

-- main focus of Biology 12

-- lacking the three structures mentioned to the left

“Eu” = True

“karyon” = nucleus

Examples of Examples of Plant/Animal CellsPlant/Animal Cells

The three differences…

Cell Cell Structures/OrganellesStructures/Organelles

All cells have a CELL MEMBRANE that All cells have a CELL MEMBRANE that acts as a “gatekeeper,” allowing only acts as a “gatekeeper,” allowing only certain molecules into/out of the cell.certain molecules into/out of the cell.

The cell membrane (mb) is therefore The cell membrane (mb) is therefore described as being SELECTIVELY described as being SELECTIVELY PERMEABLE.PERMEABLE.

The cell mb separates the The cell mb separates the cytoplasmcytoplasm (the inner contents of the cell) from the (the inner contents of the cell) from the extracellular fluid (ECF)extracellular fluid (ECF)..

The cell mb also compartmentalizes The cell mb also compartmentalizes the cell into variousthe cell into various organelles organelles which are highly specialized which are highly specialized structures with specific functions.structures with specific functions.

Organelles are to the cell as organs Organelles are to the cell as organs are to our body.are to our body.

The cell mb is a very fluid, flowing The cell mb is a very fluid, flowing structure but it does work to structure but it does work to maintain the cell’s shape (with help maintain the cell’s shape (with help from the cytoskeleton).from the cytoskeleton).

Structure of the Cell Structure of the Cell MembraneMembrane

The cell mb is made The cell mb is made up of a up of a phospholipid phospholipid bilayerbilayer along with along with embedded embedded proteinsproteins..

Carbohydrates Carbohydrates can can be found associated be found associated with the cell mb as with the cell mb as well, either attached well, either attached to the proteins or to to the proteins or to the phospholipids the phospholipids themselves.themselves.

Cholesterol!

Organelles – Organelles – small, membrane-bound small, membrane-bound structures found within the cytoplasm of the structures found within the cytoplasm of the cell.cell.

A closer look at the phospholipid molecules…

Eukaryotic Cell Eukaryotic Cell OrganellesOrganelles

A recurring theme in Biology 12 is the relationship A recurring theme in Biology 12 is the relationship between between structurestructure and and functionfunction, both at the , both at the cellular and organ system levels.cellular and organ system levels.

CELL SIZECELL SIZE- For an organism to grow, its cells must For an organism to grow, its cells must dividedivide..- Metabolic requirements impose upper limits on the Metabolic requirements impose upper limits on the

sizesize that is manageable for a single cell. that is manageable for a single cell.- As a cell (among other things) grows, its As a cell (among other things) grows, its volumevolume and and

its its surface areasurface area increase, but they do so at different increase, but they do so at different ratesrates..

- Volume is a Volume is a cubiccubic function (V(sphere) = 4/3 function (V(sphere) = 4/3ππrr33), ), whereas surface area is a whereas surface area is a quadratic quadratic function function (SA(sphere) = (SA(sphere) = 44ππrr22).).

- therefore, as a cell grows, its therefore, as a cell grows, its surface surface area-to-volume ratio (SA:V)area-to-volume ratio (SA:V) decreasesdecreases..

- It is the surface area that governs a cell’s ability to import/export materials (‘good things and bad things’)…AND…it is the volume that imposes the demands upon the cell’s surface area…thus, if the demands are increasing faster than the import/export abilities, the cell may eventually reach a point where it cannot sustain living; it will either have to divide or die.

- furthermore, a cell’s furthermore, a cell’s nucleusnucleus has a limit as has a limit as to what size of a volume that it can service.to what size of a volume that it can service.

- Once a cell Once a cell dividesdivides, its SA:V increases to a , its SA:V increases to a level that is conducive to ‘healthy living’.level that is conducive to ‘healthy living’.

Organelles, which are structures within the Organelles, which are structures within the cell that are cell that are compartmentalizedcompartmentalized by by membranes similar in structure to the cell membranes similar in structure to the cell membrane, are able to sustain many membrane, are able to sustain many different local environments that facilitate different local environments that facilitate specific metabolic functions that might be specific metabolic functions that might be incompatible with each other in an ‘open’ incompatible with each other in an ‘open’ (prokaryotic-like) cytoplasm.(prokaryotic-like) cytoplasm.

AND NOW…THE ORGANELLES AND NOW…THE ORGANELLES THEMSELVES!!!THEMSELVES!!!

NUCLEUS (fig. 3.2 p.50; 3.4 p.52)NUCLEUS (fig. 3.2 p.50; 3.4 p.52)

STRUCTURE FUNCTIONSurrounded by the nuclear envelope (bilayered membrane), which serves to separate the nucleus from the cytoplasm while also serving as a “gatekeeper”.

Main General Function: serves as the “control centre” of the cell.

The nuclear envelope possesses nuclear pores that help to determine which substances enter/exit the nucleus (generally by size).

Directs Protein Synthesis (DNA does this, serving as a “blueprint” for the production of proteins in the cytoplasm).

DNA is found here – mostly as a thread-like material called chromatin.

In fact, within the nucleus, DNA is converted to mRNA during the process called transcription.

During cell division (mitosis/meiosis), chromatin condenses into thick, cylindrical structures called chromosomes, with help from rod-like proteins called histones.

The proteins that are eventually produced (in the cytoplasm) determine the structure and function of the cell.

NUCLEOLUS (fig. 3.2 p.50; 3.4 p.52)NUCLEOLUS (fig. 3.2 p.50; 3.4 p.52)

STRUCTURE FUNCTIONLocated within the nucleus and possesses its own bi-layered membrane.

The rRNA that is produced serves as a structural element of ribosomes (another organelle found in the cytoplasm).

Has its own DNA in the form of chromatin; this DNA produces rRNA (ribosomal RNA).

Ribosomes are comprised of rRNA and specific proteins, both of which are produced in the nucleolus.

Also made up of structural proteins.

RIBOSOMES (fig. 3.2 p.50; 3.5 p.53)RIBOSOMES (fig. 3.2 p.50; 3.5 p.53)

STRUCTURE FUNCTIONConsist of two subunits, each made up of rRNA and nucleolar proteins.

Serve as the site for protein synthesis by acting as an anchor for mRNA during a process called translation.

These two subunits are not assembled until they enter the cytoplasm (so that they are small enough to exit through the pores).

Ribosomes attached to the ER produce proteins that are to be exported from the cell.

Ribosomes either attach to the endoplasmic reticulum (ER) or ‘survive’ on their own within the cytoplasm.

“Free” ribosomes produce maintenance proteins that remain inside the cell.

Ribosomes that ‘survive’ on their own sometimes group together to form polysomes.

Polysomes tend to produce maintenance proteins more rapidly.

VACUOLES (fig. 3.2 p.50)VACUOLES (fig. 3.2 p.50)STRUCTURE FUNCTION

Membranous sacs (much larger in plant cells)

Storage areas for water, sugars, salts, and other nutrients.

VESICLES (fig. 3.2 p.50; 3.5 p.53; 3.6 p.54) STRUCTURE FUNCTIONSmaller membranous sacs Serve as transporters of materials

either for export from the cell or for use in other parts of the cell.

ROUGH ENDOPLASMIC RETICULUM ROUGH ENDOPLASMIC RETICULUM (ROUGH ER) (fig. 3.2 p.50; 3.5 p.53)(ROUGH ER) (fig. 3.2 p.50; 3.5 p.53)

STRUCTURE FUNCTIONMembranous system of tubular canals (picture hollowed out linguine noodles) that branches throughout the cytoplasm.

Site for Protein Synthesis – ribosomes act as anchors for mRNA, which codes for the construction of proteins.

For the most part, it is continuous with the nuclear envelope at its beginning, and the Smooth ER at its end.

Constructed proteins then enter the lumen (interior, hollowed-out gap) of the Rough ER and are modified as they pass through towards the lumen of the Smooth ER.

Has ribosomes attached to it, making it appear ‘rough’ in texture.

Once through the Smooth ER, the proteins are placed inside a transition (transfer) vesicle, which carries the protein to the Golgi for further processing.

Very closely associated with, but not generally touching, the Golgi Body (Apparatus).

Thus, the Rough ER (and Smooth ER, for that matter) serves as a transporter, of sorts, as well.

SMOOTH ER (fig. 3.2 p.50; 3.5 p.53)SMOOTH ER (fig. 3.2 p.50; 3.5 p.53)

STRUCTURE FUNCTIONMore of a tubular type structure than the ribbon-like Rough ER (picture hollowed out spaghetti noodles).

Modifies then packages proteins created in the Rough ER into transition vesicles bound for the Golgi.

Possesses the same membrane as the Rough ER, except that there are no ribosomes attached.

Lipid synthesis (including steroids, fats, and phospholipids) – eg. Steroid hormones such as testosterone, estrogen, and aldosterone are produced in the Smooth ER. Thus, high Smooth ER numbers in testes, ovaries, and adrenal glands respectively.

Continuous with Rough ER, or, in some cases, with the nuclear membrane.

Carbohydrate synthesis and metabolism – primarily in the liver cells (converting glycogen to glucose).In the liver, Smooth ER is involved in the detoxification of drugs, including alcohol. Special vacuoles called peroxisomes are often attached to the Smooth ER, and they possess enzymes capable of detoxifying drugs.

GOLGI BODY (fig. 3.2 p.50; 3.6 p.54)GOLGI BODY (fig. 3.2 p.50; 3.6 p.54)STRUCTURE FUNCTION

Composed of a stack of 4-8 saccules (flattened sacs).

Packaging, storing, and distributing of materials produced in the ER.

One side of the stack is called the cis-face (inner face)…it is directed toward the ER and receives transition vesicles.

Modifications occur here as well (this occurs as the proteins move from saccule to saccule).

The outer face (trans-face) is directed toward the cell membrane and has secretory vesicles or transition vesicles bud off of it.

Final products are packaged into secretory vesicles that move to the cell membrane for export, or into transition vesicles for maintenance materials.

LYSOSOMES (fig. 3.2 p.50; 3.6 p.54)LYSOSOMES (fig. 3.2 p.50; 3.6 p.54)STRUCTURE FUNCTION

Large vesicles formed by the Golgi that contain hydrolytic enzymes capable of digesting (breaking down) materials into smaller, more usable bits.

Intracellular Digestion of Macromolecules such as proteins, carbohydrates, fats, and nucleic acids. The products of digestion may be sent to a mitochondrion for energy production, or may be stored in a vacuole.

Can fuse with vesicles containing materials that need to be digested.

Cell Protection – lysosomes can kill some pathogens (viruses/bacteria).Autodigestion – recycling of older cell parts.Cell Death

PEROXISOMES (fig. 3.2 p.50; 3.7 p.55)PEROXISOMES (fig. 3.2 p.50; 3.7 p.55)STRUCTURE FUNCTION

Similar in structure to lysosomes. Digest only certain organic materials where the product is hydrogen peroxide (H2O2) – some lipids and alcohol are examples.

Exist primarily in liver and kidney cells and in cells that metabolize lipids (skeletal muscles).

Toxic hydrogen peroxide is then broken down by the peroxisome-specific enzyme catalase.MITOCHONDRIA (fig. 3.2 p.50; 3.8 p.56)

STRUCTURE FUNCTIONBound with a bi-layered membrane. Powerhouses of the cell – carry out

metabolic activity by performing Aerobic Cellular Respiration –>Glucose + O2 CO2 + H2O + ATP energy

The inner membrane is folded into ‘shelves’ called christae.

Christae are directly involved in ATP energy production.

Inner fluid is called the matrix. The matrix contains enzymes capable of breaking down glucose to smaller pieces to improve the efficiency of the above rxn.

CHLOROPLASTS (fig. 3.3 p.51; 3.8 p.56)CHLOROPLASTS (fig. 3.3 p.51; 3.8 p.56)STRUCTURE FUNCTION

Found only in plant cells and plant-like protist cells.

Photosynthesis – the opposite of cellular respiration, except that the energy required is in the form of sunlight, which is fixed by the pigment chlorophyll found in the grana.

Bounded by a bi-layered membrane. Plants are autotrophs – they can produce their own glucose, then metabolize it for energy!

Coin-like thylakoids are stacked into grana and connected by lamellae tubes. The fluid in between these structures is known as stroma.

CELL WALL (fig. 3.3 p.51)CELL WALL (fig. 3.3 p.51)STRUCTURE FUNCTION

Consists of the carbohydrate cellulose, a special carb with a very rigid structure.

Provides structural strength to allow plants to grow upwards against gravity. Allows most molecules to pass through it.

CYTOSKELETON (fig. 3.2 p.50; 3.10 p.59) STRUCTURE FUNCTIONMicrotubules – cylindrical tubules comprised of the protein tubulin.Constructed by the M.T.O.C. (Microtubule Organizing Centre), which contains the centriole.

Anchor organelles and helps them move through the cytoplasm by acting as tracts.Maintains cell shape.Promotes chromosomal movement.Helps entire cell move (flagella, cilia).

Microfilaments (aka Actin Filaments) – made of the protein actin.

Muscle contractions.Cytoplasmic Streaming.Maintenance/Changes to cell shape.

Intermediate Filaments – hollow tubes of intermediate size.

Tension-bearing elements utilized to maintain cell shape.

Relationship Between Relationship Between Organelles with respect to Organelles with respect to

Importing/ExportingImporting/ExportingImportingImporting::- Cell membrane indents to form a Cell membrane indents to form a vesiclevesicle

that is sent to the target if it is a that is sent to the target if it is a hormone, hormone, enzyme, or neurotransmitterenzyme, or neurotransmitter..

- If the vesicle holds a macromolecule that is If the vesicle holds a macromolecule that is to be digested, the vesicle travels to a to be digested, the vesicle travels to a lysosomelysosome..

- If the vesicle holds a macromolecule that is If the vesicle holds a macromolecule that is to be stored, the vesicle travels to a to be stored, the vesicle travels to a vacuolevacuole..

ExportingExporting::- Proteins created at ribosomes on the Proteins created at ribosomes on the Rough ERRough ER are are

funneled into the ER’s lumen where they are funneled into the ER’s lumen where they are modified/packaged into a modified/packaged into a transition transition vesicle and sent to vesicle and sent to the cis-face of the the cis-face of the Golgi BodyGolgi Body..

- Further processing/modifying occurs in the Golgi before Further processing/modifying occurs in the Golgi before the proteins are packaged into another vesicle the proteins are packaged into another vesicle ((secretory vesiclesecretory vesicle) at the trans-face.) at the trans-face.

- Secretory vesicle travels to the cell membrane and Secretory vesicle travels to the cell membrane and releases contents into the releases contents into the extracellular fluid extracellular fluid (ECF)(ECF)

- Proteins created at ‘Proteins created at ‘freefree’ ribosomes travel through the ’ ribosomes travel through the Golgi similar to Rough-ER-produced proteins, except Golgi similar to Rough-ER-produced proteins, except that instead of being placed into a secretory vesicle, that instead of being placed into a secretory vesicle, they are placed into a they are placed into a second transition vesiclesecond transition vesicle bound bound for a lysosome (for digestion), a vacuole (for storage), or for a lysosome (for digestion), a vacuole (for storage), or anywhere else in the cell where it is in demand.anywhere else in the cell where it is in demand.

- See handout and fig. 3.6 p.54See handout and fig. 3.6 p.54

- Studying the Concepts Questions Studying the Concepts Questions #1-9 p.65#1-9 p.65

- Testing Yourself Questions #1-7, 10, Testing Yourself Questions #1-7, 10, 11.11.

- Thinking Scientifically Question #2 Thinking Scientifically Question #2 p.66p.66

- Understanding the Terms Questions Understanding the Terms Questions a-e.a-e.