Cell Biology CELL STRUCTURE Levels of Organization The

Cell Biology CELL STRUCTURE

Levels of Organization The levels of life are organized hierarchically: …from lowest to highest: n 1. ATOMS eg. carbon, oxygen atoms 2. MOLECULES eg. glucose, proteins, neutral fats, cholesterol 3. ORGANELLES (structures that make up cells) eg. nucleus, mitochondria, endoplasmic reticula 4. CELLS eg. nerve cells, smooth muscle cells 5. TISSUES (comprised of similar cells) eg. nerve tissue, muscle tissue, epithelial tissue, connective tissue

Nerve tissue – sense stimuli and transmit signals throughout animal. Muscle tissue – movement, support; three types: i. Skeletal (Striated) – voluntary bodily movements; ii. Smooth (Visceral) – involuntary contractions (blood vessels, intestine, bladder, etc); iii. Cardiac (Heart) – pumping of heart. Epithelial tissue – Protects: covers outside of body, lines organs and cavities within body. Connective tissue – binds and supports other three tissue types; six types: i. Loose Connective tissue – most widespread; attaches epithelia to other tissues and holds organs in place strong and elastic in nature; ii. Dense Connective tissue – tendons (muscle-to-bone) and ligaments (bone -to-bone); iii. Bone – mineralized (Ca 2+ & Mg 2+) for support and protection; iv. Cartilage – flexible support in certain areas (nose, ears, trachea, vertebrae); v. Blood – ‘connects’ different parts of body by transporting materials; vi. Fat (Adipose) tissue – pads and insulates body. 6. ORGANS (comprised of various tissue-types)

8. ORGANISM (comprised of organ systems) eg. human beings, cats, wildebeest 9. POPULATIONS/COMMUNITIES Definition: CELL – the structural and functional unit of life. It is the smallest structure capable of performing all of the functions necessary for life. FUNCTIONS NECESSARY FOR LIFE: 1. Reproduce ON OWN! (excludes viruses which require cells to repr. ) 2. Grow 3. Respire (Metabolize) – Cellular Respiration (mitochondria) glucose (C 6 H 12 O 6) + O 2 CO 2 + H 2 O + ATP energy 4. Contain genetic material (RNA and DNA) 5. Respond to stimuli

Macromolecules Making Up Cells 1. 2. 3. 4. - Carbohydrates (energy, identification) Proteins (energy, digestion, structure, hormones etc) Lipids (incl. fats, steroids) – (energy, insulation, hormones, cushioning) Nucleic Acids (RNA/DNA) – (blueprint for proteins) All of these molecules are made up of atoms (elements); the main elements comprising living organisms are: C, H, N, O.

Classifying Cells CELLS PROKARYOTIC -- smaller, less organized -- lack a true nucleus -- lack membrane-bound organelles -- single circular chromosome -- bacteria EUKARYOTIC -- have a true nucleus with a cell membrane -- possess membranebound organelles -- 10 X size of prok. cells -- focus of Biology 12

Eukaryotic Cells Plant Cells “Eu” = True “karyon” = nucleus Animal Cells -- p. 51 Figure 3. 3 -- p. 50 Figure 3. 2 -- possess a cell wall -- have chloroplasts -- main focus of Biology 12 -- large, contractile vacuole -- lacking the three structures mentioned to

Examples of Plant/Animal Cells The three differences…

Cell Structures/Organelles All cells have a CELL MEMBRANE that acts as a “gatekeeper, ” allowing only certain molecules into/out of the cell. n The cell membrane (mb) is therefore described as being SELECTIVELY PERMEABLE. n The cell mb separates the cytoplasm (the inner contents of the cell) from the extracellular fluid (ECF). n

The cell mb also compartmentalizes the cell into various organelles which are highly specialized structures with specific functions. n Organelles are to the cell as organs are to our body. n The cell mb is a very fluid, flowing structure but it does work to maintain the cell’s shape (with help from the cytoskeleton). n

Structure of the Cell Membrane n n The cell mb is made up of a phospholipid bilayer along with embedded proteins. Carbohydrates can be found associated with the cell mb as well, either attached to the proteins or to the phospholipids themselves. Cholesterol !

A closer look at the phospholipid molecules… n Organelles – small, membrane-bound structures found within the cytoplasm of the cell.

Eukaryotic Cell Organelles A recurring theme in Biology 12 is the relationship between structure and function, both at the cellular and organ system levels. CELL SIZE - - As cells mature (post-mitosis), they grow. However, for an organism to grow, its cells must divide. Metabolic restrictions impose limits on the max. size of a cell. As a cell grows, its volume and its surface area increase, but they do so at different rates. In fact, V grows faster than SA.

- therefore, as a cell grows, its surface area-to -volume ratio (SA: V) decreases. - The SA of a cell governs its ability to import/export materials. - The V of a cell (the part of the cell housing the organelles) imposes the demands upon the cell’s SA. - 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

furthermore, a cell’s nucleus has a limit as to what size of a volume that it can service. - Once a cell divides, its SA: V increases to a level that is conducive to ‘healthy living’. Organelles, which are structures within the cell that are compartmentalized by membranes similar in structure to the cell membrane, are able to sustain many different local environments that facilitate specific metabolic functions that might be incompatible with each other in an ‘open’ (prokaryotic-like) cytoplasm. - AND NOW…THE ORGANELLES THEMSELVES!!!

NUCLEUS (fig. 3. 2 p. 50; 3. 4 p. 52) STRUCTURE Surrounded by the nuclear envelope (bilayered membrane), which serves to separate the nucleus from the cytoplasm while also serving as a “gatekeeper”. FUNCTION Main General Function: serves as the “control centre” of the cell. The nuclear envelope possesses nuclear Directs Protein Synthesis (DNA does this, pores that help to determine which substances serving as a “blueprint” for the production of enter/exit the nucleus (generally by size). 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 m. RNA 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) STRUCTURE Located within the nucleus and possesses its own bi-layered membrane. FUNCTION The r. RNA 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; Ribosomes are comprised of r. RNA and this DNA produces r. RNA (ribosomal RNA). 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) STRUCTURE FUNCTION Consist of two subunits, each made up of r. RNA and nucleolar proteins. Serve as the site for protein synthesis by acting as an anchor for m. RNA 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 Polysomes tend to produce maintenance sometimes group together to form polysomes. proteins more rapidly.

VACUOLES (fig. 3. 2 p. 50) STRUCTURE Membranous sacs (much larger in plant cells) FUNCTION Storage areas for water, sugars, salts, and other nutrients. VESICLES (fig. 3. 2 p. 50; 3. 5 p. 53; 3. 6 p. 54) STRUCTURE Smaller membranous sacs FUNCTION Serve as transporters of materials either for export from the cell or for use in other parts of the cell.

ROUGH ENDOPLASMIC RETICULUM (ROUGH ER) (fig. 3. 2 p. 50; 3. 5 p. 53) STRUCTURE FUNCTION Membranous system of tubular canals (picture hollowed out linguine noodles) that branches throughout the cytoplasm. Site for Protein Synthesis – ribosomes act as anchors for m. RNA, 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) STRUCTURE FUNCTION More 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) 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 Final products are packaged into secretory the cell membrane and has secretory vesicles that move to the cell membrane for or transition vesicles bud off of it. export, or into transition vesicles for maintenance materials.

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) STRUCTURE FUNCTION Similar in structure to lysosomes. Digest only certain organic materials where the product is hydrogen peroxide (H 2 O 2) – 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. 9 p. 57) STRUCTURE FUNCTION Bound with a bi-layered membrane. Powerhouses of the cell – carry out metabolic activity by performing Aerobic Cellular Respiration –> Glucose + O 2 CO 2 + H 2 O + 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) 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) STRUCTURE Consists of the carbohydrate cellulose, a special carb with a very rigid structure. FUNCTION 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 FUNCTION Microtubules – 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 Organelles with respect to Importing/Exporting Importing: - Cell membrane indents to form a vesicle that is sent to the target if it is a hormone, enzyme, or neurotransmitter. - If the vesicle holds a macromolecule that is to be digested, the vesicle travels to a lysosome. - If the vesicle holds a macromolecule that is to be stored, the vesicle travels to a vacuole.

Exporting: - - - Proteins created at ribosomes on the Rough ER are funneled into the ER’s lumen where they are modified/packaged into a transition vesicle and sent to the cis-face of the Golgi Body. Further processing/modifying occurs in the Golgi before the proteins are packaged into another vesicle (secretory vesicle) at the trans-face. Secretory vesicle travels to the cell membrane and releases contents into the extracellular fluid (ECF) Proteins created at ‘free’ ribosomes travel through the Golgi similar to Rough-ER-produced proteins, except that instead of being placed into a secretory vesicle, they are placed into a second transition vesicle bound for a lysosome (for digestion), a vacuole (for storage), or anywhere else in the cell where it is in demand. See handout and fig. 3. 6 p. 54

- - Studying the Concepts Questions #1 -9 p. 65 Testing Yourself Questions #1 -7, 10, 11. Thinking Scientifically Question #2 p. 66 Understanding the Terms Questions a-e.