Chapter 3 Part 1: Cell Structure and Function PDF

# Chapter 3 part 1 ## 3 Main Parts: 1. Nucleus 2. Cytoplasm 3. Cell Membrane ## The Nucleus: 1. **Nuclear Envelope** - Consists of double membranes that bounds the nucleus. - Contains nuclear pores that serve as the site of protein synthesis. 2. **Nucleoli** - Sites of ribosome synthes...

# Chapter 3 part 1 ## 3 Main Parts: 1. Nucleus 2. Cytoplasm 3. Cell Membrane ## The Nucleus: 1. **Nuclear Envelope** - Consists of double membranes that bounds the nucleus. - Contains nuclear pores that serve as the site of protein synthesis. 2. **Nucleoli** - Sites of ribosome synthesis and assembly. - Ribosomes migrate into the cytoplasm through nuclear pores to serve as the site of protein synthesis. 3. **Chromatin** - It's the combination of DNA + proteins in resting cells. - As cells prepare for dividing chromatin threads, then condenses to chromosomes. ## Plasma Membrane: - Hydrophilic head, hydrophobic tail. - **Lipid Bilayer** - Fluid Mosaic Model: It's a phospholipid bilayer with cholesterol + proteins + glycoproteins placed in various configurations. - The layer helps in regulation of water (restricts the movement). - Glycoproteins function as receptors (help in movements within the cell). - Enzymes, transport proteins, ion channels, structural proteins, etc... - Sugars and glycoproteins are sticky (gives plasma membrane a fuzzy appearance). - Forms the glycocalyx. - **Glycolipids** (receptors or antigens). - **Channels** - Control what goes in and out, and requires ATP. - **Proteins** - Holds the lipid bilayer together. - Vertical and horizontal proteins. ## Membrane Junctions - Ways cells are attached: - Glycoproteins - Wavy contours of plasma membranes of adjacent cells - Special membrane junctions - **Tight Junctions:** - Plasma membranes of ADJACENT cells. - Leak-proof (not allowing any molecule out). - Ex: Cells forming walls of the small intestine. - **Gap Junctions:** - Hollow protein cylinder (connexons) that directly attach adjacent cells. - Enabling them to exchange substances (nutrients, ions, etc.). - **Desmosomes:** - Anchoring junctions; holds cells from breaking off (heart muscle and skin cells). - Thickened plasma membrane (plaque) connected together by fine protein filaments. ## Cytoplasm - Area of most cell activities. 1. **Cytosol** - Water + dissolved nutrients and other elements. 2. **Cellular Organelles** 3. **Cytoplasmic Inclusions:** - Stored fat in fat cells (adipocytes). - Glycogen in liver cells (hepatocytes). - Pigments in skin cells (keratinocytes). ## Mitochondria - Surrounded by a double membrane (outer and inner membranes). - Inner membrane has protrusions (cristae) helps in increasing the surface area. - Contains enzymes (needs the enzymes for ATP production). - Maternal genetic material is present. - Produces ATP by cellular respiration. ## Endoplasmic Reticulum 1. **Rough ER:** Ribosomes are attached to the surface. - Participates in protein synthesis. - The synthesized protein transports and attaches to receiving phase (Golgi Apparatus). 2. **Smooth ER:** Plays no role in protein synthesis. - Participates in lipid metabolism (cholesterol and fat synthesis). - Detoxifies drugs and pesticides. - Produces steroid hormones (ex: male testes producing testosterone). ## Synthesis and Export of a Protein 1. As the protein is synthesized on the ribosome, it migrates into the rough ER cistern. 2. In the cistern, the protein folds into its functional shape. Short sugar chains may be attached to the protein (forming a glycoprotein). 3. The protein is packaged in a tiny membranous sac called a transport vesicle. 4. The transport vesicle buds from the rough ER and travels to the Golgi apparatus for further processing. ## Golgi Apparatus - Stack of flattened membranous sacs (with many vesicles fusing in and budding off). - Modifies and packages incoming proteins. - Vesicles move in 1 of 3 pathways: - **Pathway 1:** A vesicle carries the proteins and attaches to the cell membrane to perform exocytosis. - **Pathway 2:** Empty vesicles bud out of golgi apparatus; fuses with plasma membrane and enables cells to increase in size. - **Pathway 3:** Vesicles containing digestive enzymes become lysosomes; fuses with ingested substances to degrade them (ex: pathogens). ## Lysosomes - Membranous bags filled with digestive enzymes. - Recycling purposes. - Has an ability to degrade macromolecules (phagocytes, macrophages, etc). ## Peroxisomes - Membranous bags of oxidative enzymes (oxidases). - Detoxifies poisons, alcohol, and other harmful substances. - **Free radicals:** By-products of cellular metabolism that if accumulated can damage proteins and DNA. Peroxisomes convert free radicals into H₂O₂; excess H₂O₂ is converted into H₂O by the catalase enzyme. ## Cytoskeleton 1. **Microfilaments:** Involved in cell mobility and changing shape of a cell (ex: Actin and Myosin). 2. **Intermediate filaments:** Form desmosomes; acts like internal anchors that resist pulling forces on the cell. 3. **Microtubules:** Gives the cell its overall shape; helps in distributing and locking organelles in place. - **Important** during cell division. ## Structures related to Cytoskeleton: 1. **Centrioles:** Paired rod-shaped bodies near nucleus; forms microtubules and spindle fibers (plays a major role in cellular division). 2. **Cell extensions with microtubules or actin filaments as the core structure:** - **Cilia:** Multiple whip-like projections that move liquid current along surface of cells. Originates from centrioles (microtubules). - **Flagella:** Longer/thicker/smaller in number than cilia; consists of microtubules (sperm cells, bacterial flagella). - **Microvilli:** Tiny fingerlike extensions of cell membrane (involved in absorption; epithelial cells of small intestine). ## Cell Diversity - Over 200 different types of cells make the body. - Cells vary in size, shape, structure, function, etc. - Can be divided into several groups based on general function. ## Membrane Transport - Movement of the molecules (small substances). 1. **Passive transport:** No energy needed (diffusion, filtration, and facilitated diffusion). 2. **Active transport:** ATP is needed (ion channels like Na+/K+ pump). ## Osmosis 1. **Isotonic:** Equal solute and water concentrations. Causes no change in the cell. 2. **Hypertonic:** More solutes than the cells. Cells will begin to shrink. 3. **Hypotonic:** Fewer solutes, more water. Cells will plump or burst. ## Active Transport - Energy-dependent. - Substances move against concentration gradient. - ex: Na/k pump. ## Vesicular Transport (Type of Active Transport) 1. **Exocytosis** 2. **Endocytosis** - **Phagocytosis:** Engulfs solids into the cell. - **Pinocytosis:** Gulps droplets of water the cell. - **Transmembrane proteins** on the vesicles are called **V-SNARES ** (V for vesicle). - **Plasma membrane proteins** are called **t-SNARES** (t for target). - **V-SNARES** recognize and bind to **t-SNARES**. ## Cell Physiology - Cells have the ability to: - Metabolize - Grow - Digest food - Move - Dispose of waste - Reproduce - Respond to a stimulus ## Solution - The inside of a cell and the environment in which cells live is water + substances dissolved in water. - A solution is a homogenous mixture of ≥ 2 substances. - **Most abundant substance in a solution is the solvent (water), the rest are solutes.** **Examples of solutions in the human body:** 1. Blood plasma: The liquid phase of blood; rich in proteins of other substances (minerals, vitamins, hormones, etc.). It can move out of circulation to become interstitial fluid. 2. Intracellular fluid: Located inside the cells (nucleoplasm and cytosol). Contains gases, nutrients, and salts dissolved in water. 3. Interstitial fluid: Fluid that fills the spaces between cells; contains gases, nutrients, hormones, etc. ## Movement of Large Substances 1. **Vesicular transport** - Endocytosis or exocytosis ## Diffusion - Movement of molecules from higher to lower concentration. - Molecules should be small. - Molecules should be lipid-soluble. - Molecules are assisted by a membrane carrier. ## Types of Diffusion: 1. **Simple diffusion** 2. **Osmosis** (movement of water) 3. **Facilitated diffusion** (carrier mediated, channel mediated) ## Osmosis 1. **Isotonic:** Equal solute and water concentrations. Causes no change in the cell. 2. **Hypertonic:** More solutes than the cells. Cells will begin to shrink. 3. **Hypotonic:** Fewer solutes, more water. Cells will plump or burst. ## Active Transport - Energy-dependent. - Substances move against concentration gradient. - ex: Na/k pump. ## Vesicular Transport (Type of Active Transport) 1. **Exocytosis** 2. **Endocytosis** - **Phagocytosis:** Engulfs solids into the cell. - **Pinocytosis:** Gulps droplets of water into the cell. - **Transmembrane proteins** on the vesicles are called **V-SNARES ** (V for vesicle). - **Plasma membrane proteins** are called **t-SNARES** (t for target). - **V-SNARES** recognize and bind to **t-SNARES**.