Cell Biology: Cell Structure and Function PDF

Last edited: 9/6/2021 3. CELL STRUCTURE AND FUNCTION Cell Biology | Cell Structure & Function Medical Editor: Abigail Xu, RPh OUTLINE...

Last edited: 9/6/2021 3. CELL STRUCTURE AND FUNCTION Cell Biology | Cell Structure & Function Medical Editor: Abigail Xu, RPh OUTLINE (B) NUCLEOLUS Site of rRNA synthesis I) NUCLEUS Ribosome synthesis II) ENDOPLASMIC RETICULUM (E.R.) o Ribosome= rRNA + small proteins III) GOLGI APPARATUS IV) CELL MEMBRANE (C) CHROMATIN V) LYSOSOMES VI) PEROXISOMES DNA + Histone proteins VII) MITOCHONDRIA Make up the genetic material VIII) RIBOSOMES (1) Euchromatin IX) CYTOSKELETON X) REVIEW QUESTIONS Loose chromatin XI) REFERENCES Location: center of nucleus Function o Expression of DNA o Transcribe DNA I) NUCLEUS o Make different types of mRNA o Replication Brain of the cell Center of cell (2) Heterochromatin Tied chromatin Location: closer to inner membrane of nuclear envelope (D) DNA (1) DNA Replication Produce DNA from DNA (2) Transcription DNA → RNA Different types of RNA o tRNA o mRNA o rRNA II) ENDOPLASMIC RETICULUM (E.R.) (A) ROUGH E.R. Filamentous network Contain ribosomes Figure 1. Parts of the Nucleus of Cell (A) NUCLEAR ENVELOPE (1) Outer Membrane Features numerous ribosomes attached to the surface Importance of Ribosomes in outer layer o DNA is converted to mRNA in nucleus o mRNA move out of nucleus via nuclear pore o mRNA attach to ribosomes o move to rough endoplasmic reticulum (ER) (2) Inner Membrane Lamins o protein structure that binds to DNA and histones, controlling cell division o Control  Structure of nuclear envelope  Cell division  Interact with chromatin o Mutation can cause progerias (3) Nuclear Pores Figure 2. Summary of Function of Rough E.R. transport ions, proteins, and nucleotides in and out of nucleus (cytoplasm to nucleus, nucleus to cytoplasm) Contains special transporters Cell Structure and Function CELL BIOLOGY: Note #1. 1 of 7 (1) Site of Protein Synthesis (iii) Cholesterol Recall: Can become steroid hormones o DNA in nucleus can undergo transcription o Progesterone  DNA → mRNA o Testosterone o mRNA bind to ribosome in Rough E.R. o Estrogen o Translation Precursor molecules are taken up in the Smooth E.R.  mRNA → protein Enzymes in smooth E.R. use the precursors to produce Rough E.R.: site of protein synthesis lipid molecules Proteins synthesized in Rough E.R. Lipid molecules are released from the Smooth E.R. o Lysosomes through vesicles o Membrane of organelles and cell The vesicles containing the lipid molecules can be sent to o Proteins that are excreted the Golgi or cell membrane to release cholesterol, fatty acids, or phospholipids (2) Protein Folding Proteins need to be folded in a particular way to be (2) CYP 450 Enzymes functional Important in detoxification Site: Liver (contains many CYP 450) (3) Glycosylation (N-type) Breaks down the following via Biotransformation/ Rough E.R. contains enzymes that can add little sugar Xenobiotic Metabolism residues to protein to activate it o Toxins o Drugs (4) Packaging Proteins o Alcohol Proteins bud into the Rough E.R. and packaged in vesicles (3) Glucose-6-Phosphate Metabolism Vesicles containing the protein (that will become Glycogen lysosomal, membrane, or excreted protein) will be o Stored in cell transported to the Golgi Apparatus o polymer of glucose Summary Protein Synthesis in Rough E.R. o when body needs energy, glycogen can be broken down into glucose mRNA from the nucleus is bound to ribosome and transported to Rough E.R. Glucose-6-Phosphate translated to protein o Intermediate in the breakdown of glycogen to glucose protein is pushed into the filamentous network of rough Glucose-6-Phosphatase E.R. o Enzyme in Smooth E.R. protein folding o removes phosphate in the 6th carbon of Glucose-6- add sugar residue on folded protein activate protein Phosphate, converting it to glucose package protein in vesicles to be transported to Golgi (4) Stores Ca2+ Apparatus Sarcoplasmic reticulum (B) SMOOTH E.R. o Found in organs that contain lots of calcium (i.e., No ribosomes muscle cells) Contain different enzymes, particularly those involved in o analogous to smooth E.R. lipid synthesis o store calcium o contains pumps that release calcium into cytoplasm when needed during:  transport process  muscle contraction III) GOLGI APPARATUS Vesicles packed with proteins and lipids from the Rough E.R. and Smooth E.R., respectively, are sent to the Golgi Packaging organelle Figure 3. Summary of Function of Smooth E.R. (1) Lipid synthesis Types of Lipids Synthesized: (i) Fatty acids (ii) Phospholipids Figure 4. Summary of Function of Golgi Apparatus 2 of 7 CELL BIOLOGY: Note #1. Cell Structure and Function  (A) ANATOMICAL STRUCTURE OF GOLGI (A) COMPONENTS OF CELL MEMBRANE (1) Cis Golgi (1) Phospholipid Bilayer Side that faces the endoplasmic reticulum (i) Phospholipid Head Receives the vesicles from the smooth and rough E.R. Polar: water soluble (2) Trans Golgi Hydrophilic: interact with water Side where vesicles are released out of the Golgi, going Negative charges towards lysosomes, cell membrane, etc. Inner surface of membrane: pointing inwards Outer surface of membrane: pointing outwards (B) FUNCTION OF GOLGI (ii) Fatty Acid Tail (1) Receive vesicles from Rough and Smooth E.R. Saturated with Hydrogen Vesicles contain: Nonpolar o proteins containing different sugar molecules Hydrophobic: don’t like to interact with water o lipids No negative or slight changes in charge (2) Modification of proteins Point towards each other (2) Cholesterol (i) Glycosylation Came from Smooth E.R. packaged and sent to Golgi and Adding sugar residues then the cell membrane Types: Controls fluidity of membrane a. N-type ↑cholesterol → ↓space between phospholipids → ↓fluidity o add sugar residue on Nitrogen component of ↓cholesterol→ ↑space between phospholipid → ↑fluidity protein b. O-type (3) Proteins o only the Golgi can do O-type glycosylation Various functions o add sugar residue on Oxygen component of o Transporters protein o Enzymes (ii) Phosphorylation o Linker proteins between cells I-cell disease: disease related to phosphorylation (i) Integral Proteins (3) Package Molecules (ii) Peripheral Proteins Modified proteins and lipids move through Golgi and pop (B) FUNCTION: off the trans Golgi in vesicles BARRIER FOR TRANSPORT PROCESSES The molecules can become: Selectively permeable barrier o Lysosomal proteins Only allows particular diffusion o Membrane proteins o Excreted out of cell Cell transport processes Moving materials into and out of cell, crossing cell IV) CELL MEMBRANE membrane (1) Simple Diffusion (2) Facilitated Diffusion (3) Vesicular Transport V) LYSOSOMES Spherical organelles Contain hydrolytic enzymes Figure 5. Summary of Structure and Function of Cell Membrane Figure 6. Summary of Function of Lysosomes Cell Structure and Function CELL BIOLOGY: Note #1. 3 of 7  (A) TYPES OF HYDROLYTIC ENZYMES (1) Catalase (1) Proteases (2) Oxidase Break down proteins (3) Metabolic Enzymes (2) Nucleases (B) FUNCTION Break down nucleic acids (1) Protect from Oxidative Damage by Free Radicals (3) Lipases Catalase and Oxidase Break down lipids When a cell takes in oxygen, oxygen (O2) can get converted to free radicals: (4) Glucosidases o superoxide anion (O2-) Break down carbohydrates o hydrogen peroxide (H2O2) o hydroxyl radical (B) IMPORTANCE OF HYDROLYTIC ENZYMES Free Radicals are dangerous (1) Break down macromolecules o Bind to proteins, nucleic acid, cell membrane Macromolecules can be brought into cell via: Hydrogen Peroxide o White Blood Cell: Phagocytosis o Accumulate in peroxisomes due to fatty acid o Clathrin-coated mediated endocytosis metabolism Macromolecules: Catalase o Proteins o Break down hydrogen peroxide into water and o Nucleic Acids oxygen, which are not harmful for the cell o Lipids (2) Fatty Acid Oxidation o Carbohydrates Catalase (2) Autophagy of Organelles o catalyzes the first step in the break down fatty acids When organelles (i.e. mitochondria, cytoskeleton, Types: ribosomes, etc.) reach the end of their functional capacity, they are recycled (i) α-oxidation Lysosomes take and package the organelles breaks down branched chain fatty acids to o Surround the organelle with vesicles acetyl-CoA o Send to lysosome o Hydrolytic enzymes will breakdown the organelle (ii) β-oxidation  Ribosomes: made up of protein & RNA breaks down very long chain fatty acids to Broken down by proteases and nucleases acetyl-CoA (3) Autolysis of Damaged Cells (3) Make Lipids and Cholesterol Severely damaged cells beyond repair Acetyl-CoA from fatty acid oxidation can be utilized to Lysosome bust open make lipids Hydrolytic enzymes are released All macromolecules of cell are broken down (i) Plasmalogen myelin in the white mater of brain VI) PEROXISOMES issues in peroxisomes can lead to Spherical organelle Contain different enzymes (ii) Cholesterol Steroid hormones Bile acids (4) Ethanol Metabolism Catalase o Break down ethanol VII) MITOCHONDRIA Powerhouse of cell Site of ATP synthesis (A) STRUCTURE (1) Outer Membrane Smooth membrane High permeability: many transport proteins Figure 7. Summary of Enzymes and Function of Peroxisomes (2) Inner Membrane Folded Cristae (A) ENZYMES o inwardly projecting folds of the inner membrane of mitochondria 4 of 7 CELL BIOLOGY: Note #1. Cell Structure and Function  less permeable to transport of molecules going in and out (iv) Gluconeogenesis (3) Matrix Convert amino acids, glycerol, and odd-chain fatty acids into glucose Site of metabolic reactions Location of mitochondrial DNA (MTDNA) (v) Ketogenesis Make ketone bodies from acetyl-CoA (C) MITOCHONDRIAL DNA Comes from the mother Makes proteins that are involved in metabolic reactions VIII) RIBOSOMES Figure 8. Summary of Structure and Function of Mitochondria (B) FUNCTION (1) ATP Synthesis Two ways of ATP synthesis: (i) Oxidative phosphorylation Occurs in inner membrane of mitochondria Involve flow of electrons through the electron transport chain (ETC) (ii) Substrate level phosphorylation Figure 9. Structure and Function of Ribosomes (2) Metabolic reactions (A) STRUCTURE (i) Krebs cycle (1) Components Acetyl-CoA Citrate (i) Large Subunit Isocitrate Eukaryotic cells: 60s (s= Svedberg unit) α-ketoglutarate Succinyl-CoA (ii) Small Subunit Succinate Eukaryotic cells: 40s Fumarate Malate (2) rRNA + Proteins Oxaloacetate (ii) Heme synthesis (3) Types based on Location Component of different pigment molecules that (i) Membrane-bound ribosomes are part of the ETC Bound to rough E.R. Hemoglobin Myoglobin (ii) Cytosolic/ free ribosomes (iii) Urea cycle Cytosol Converting different molecules (i.e. Ammonia) into Urea Cell Structure and Function CELL BIOLOGY: Note #1. 5 of 7  (B) FUNCTION: PROTEIN SYNTHESIS (TRANSLATION) Ribosomes take mRNA and tRNA and make protein (1) Membrane-bound ribosomes Produce proteins that will become part of: o Lysosomes o Membrane (integral or peripheral proteins) o Proteins excreted out of cell (2) Cytosolic ribosomes Produce cytosolic proteins and enzymes that will not leave the cell Enzymes involved in the metabolic pathways that occur in the cytosol IX) CYTOSKELETON Scattered all over the cell Figure 11. Summary of Intermediate Filaments Function (A) MICROFILAMENTS (ACTIN) (C) MICROTUBULES Made up of two types of proteins (i) α-tubulin (ii) β-tubulin α and β-tubulin come together to form filaments 13 filaments come together to form the microtubular structure Figure 10. Function of Actin (1) Muscle Contraction Actin binds to myosin in contractile cells to cause contraction and relaxation of muscles (2) Cytokinesis of Mitosis Mitosis: cell division Actin forms the constriction ring around the central portion of cell Squeeze cell to split one cell into two daughter cells (3) Diapedesis of White Blood Cell (WBC) Move WBC from the blood to the tissues Diapedesis Figure 12. Summary of Function of Microtubules o WBC move through the intact walls of capillaries (1) Intracellular Motor Protein Transport o Vessels are lined with endothelial cells o Actins polymerize and alter shape of WBC so that it Motor proteins on the microtubules can squeeze out of the endothelial cells (i) Dynein (4) Phagocytosis of WBCs (ii) Kinesin Actins create pseudopods from WBC that surround o Bind to organelles and vesicles (contain proteins, pathogen lipids, etc. that are moving towards cell membrane or bringing into cell) (B) INTERMEDIATE FILAMENTS o Transport the contents of vesicles to different places High tensile o Railway system Not much movement o Utilizes ATP (1) Anchor Cell to Extracellular Matrix (2) Cell Division Extracellular matrix Mitosis o protein network around cell Chromosomes are lined up during metaphase o composed of collagen, elastin, other proteins Centromere: constriction region at the center of chromosome (2) Connect Cell to Cell Kinetochore: found on the side of centromere Anchor cell to one another Microtubules connect to kinetochore Depolymerization of microtubules (3) Anchor Organelles inside of Cell Separates chromosomes into sister chromatids So that organelles will not just float around 6 of 7 CELL BIOLOGY: Note #1. Cell Structure and Function  (3) Cell Extension Microtubules make up base of cellular extension Motor proteins (Dynein and Kinesin) are incorporated into cellular extensions o utilize ATP o Create beating or twisting-like motion (i) Cilia Respiratory tract: clear out mucus Fallopian tube: movement of oocyte or ovum towards uterus (ii) Flagella Sperm: movement towards secondary oocyte X) REVIEW QUESTIONS 1) Which organelle is the main site of ATP synthesis? a) Nucleus b) Mitochondria c) Golgi apparatus d) Peroxisome 2) Function of lysosome: a) Transport materials b) Destroy old cell parts c) Package proteins d) Barrier 3) Site of ribosome synthesis: a) Endoplasmic reticulum b) Lysosome c) Nucleolus d) Mitochondria 4) Only organelle that can do O-type glycosylation a) Rough ER b) Golgi Apparatus c) Cytoskeleton d) Smooth ER 5) Controls what enters and leaves the cell a) Nucleus b) Cell membrane c) Golgi apparatus d) Ribosomes 6) Main function is protein synthesis a) Lysosome b) Rough ER c) Ribosome d) Smooth ER 7) Site of Heme Synthesis a) Nucleus b) Cytoskeleton c) Mitochondria d) Ribosome 8) Enzyme involved in ethanol metabolism a) Catalase b) Nuclease c) Protease d) Lipase 9) Involved in muscle contraction a) Intermediate filaments b) Cilia c) Dynein d) Actin 10) Anchors organelles inside the cell a) Microtubule b) Actin c) Myosin d) Intermediate Filaments CHECK YOUR ANSWERS XI) REFERENCES Cell Structure and Function CELL BIOLOGY: Note #1. 7 of 7