SI2101 Cell Structure PDF

Cell Structure SI2101 Dr. Nicole Burns Lecture adapted from: Dr. Amir Shafat [email protected] Learning Outcomes Describe the structure and function of a typical cell Describe the structure and function of the major organelles...

Cell Structure SI2101 Dr. Nicole Burns Lecture adapted from: Dr. Amir Shafat [email protected] Learning Outcomes Describe the structure and function of a typical cell Describe the structure and function of the major organelles University ofGalway.ie Cell Structure and Protein Function Structure determines function. That which alters structure alters function. Cells: Membranes ─ internal and external par ons nucleus─ genomic DNA Ribosomes ─ protein synthesis endoplasmic re culum─ synthesis and calcium dynamics Golgi apparatus─ secreted proteins mitochondria─ ATP synthesis miscellaneous organelles University ofGalway.ie Cell structure and protein function cont. Central dogma: genes to proteins transcription (DNA to RNA) splicing (RNA to mRNA) translation (mRNA code determines amino acid sequence in protein synthesis) ATP/chemical energy: substrate/oxidative phosphorylation Enzymes and metabolic pathways University ofGalway.ie  Figure 3.1 Typical Sizes of Cell Structures Sizes, on a log scale © McGraw Hill, LLC 5  Figure 3.2 Electron Micrograph of a Thin Section Through a Portion of a Human Adrenal Cell, Showing the Appearance of Intracellular Organelles Don W. Fawcett/Science Source © McGraw Hill, LLC 6  Figure 3.3 Structures Found in Most Human Cells Organelles have their own membranes © McGraw Hill, LLC 7  Table 3.1 TABLE 3.1 Functions of Plasma Membranes 1. Regulate the passage of substances into and out of cells and between cell organelles and cytosol 2. Detect chemical messengers arriving at the cell surface 3. Link adjacent cells together by membrane junctions 4. Anchor cells to the extracellular matrix Copyright © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 8  Figure 3.5 Electron Micrograph of a Human Red Blood Cell Plasma Membrane and Schematic Arrangement of Proteins, Phospholipids, and Cholesterol in a Membrane NIBSC/Science Photo Library/Science Source (a) Plasma membrane of a red (b) Components of a plasma blood cell. membrane. Access the text alternative for slide images. © McGraw Hill, LLC 9  Figure 3.6 Arrangement of Integral and Peripheral Membrane Proteins in a Lipid Bilayer © McGraw Hill, LLC 10  Figure 3.7 Typical Transmembrane Protein © McGraw Hill, LLC 11  Figure 3.8 Fluid-Mosaic Model of Plasma Membrane Structure © McGraw Hill, LLC 12 Membrane Junctions Many cells are physically joined in certain locations along their membranes by specialized types of junctions, including desmosomes, tight junctions, and gap junctions. Integrins are transmembrane proteins that bind to specific proteins in the extracellular matrix and link them to membrane proteins on adjacent cells. University ofGalway.ie Desmosomes provide strong attachments Figure 3.9a University ofGalway.ie Tight Junctions Figure 3.9b University ofGalway.ie Gap Junctions communicate and coordinate Figure 3.9d University ofGalway.ie  Figure 3.9c Electron micrograph of intestinal cells Don W. Fawcett/Science Source © McGraw Hill, LLC 17  Figure 3.10 Nucleus and Nucleolus Don W. Fawcett/Science Source Don W. Fawcett/Science Source Nucleus Nucleolus © McGraw Hill, LLC 18 University ofGalway.ie  University ofGalway.ie ©2003 Brooks/Cole, Thomson learning  Nucleus The DNA code is ‘transcribed’ into mRNA Ribosomes The mRNA is ‘translated’ to give instructions for protein synthesis Figure 3.16 The Expression of Genetic Information in a Cell - From Transcription to Translation to Protein University Synthesis ofGalway.ie 27  Transcription, Translation, and Protein Synthesis Proteins are involved in all physiological processes, from cell signaling to tissue remodeling to organ function. Remember: © McGraw Hill, LLC 28 Figure 3.17 The Sequence of Three-Letter Code Words in a Gene Determines the Sequence of Amino Acids in a Polypeptide Chain GENES “CODE FOR” PROTEINS The “triplet code” of DNA determines which amino acid will be placed in each position of the protein. University ofGalway.ie 29 Figure 3.19 Spliceosomes Ultimately Form the Mature mRNA Molecule that Passes Through the Nuclear Pores to the Cytosol University ofGalway.ie 30  Figure 3.21 Sequence of Events During Protein Synthesis by a Ribosome Arrow indicates movement of the ribosome along the mRNA. © McGraw Hill, LLC 31  Figure 3.22 Several Ribosomes can Simultaneously Move Along a Strand of mRNA, Producing the Same Protein in Different Stages of Assembly Access the text alternative for slide images. © McGraw Hill, LLC 32  Table 3.2 TABLE 3.2 Events Leading from DNA to Protein Synthesis Transcription RNA polymerase binds to the promoter region of a gene and separates the two strands of the DNA double helix in the region of the gene to be transcribed. Free ribonucleotide triphosphates base-pair with the deoxynucleotides in the template strand of DNA. The ribonucleotides paired with this strand of DNA are linked by RNA polymerase to form a primary RNA transcript containing a sequence of bases complementary to the template strand of the DNA base sequence. RNA splicing removes the intron-derived regions, which contain noncoding sequences, in the primary RNA transcript and splices together the exon-derived regions, which encode specific amino acids, producing a molecule of mature mRNA. Translation The mRNA passes from the nucleus to the cytoplasm, where one end of the mRNA binds to the small subunit of a ribosome. Free amino acids are linked to their corresponding tRNAs by aminoacyl-tRNA synthetase. The three-base anticodon in an amino acid–tRNA complex pairs with its corresponding codon in the region of the mRNA bound to the ribosome. The amino acid on the tRNA is linked by a peptide bond to the end of the growing polypeptide chain. The tRNA that has been freed of its amino acid is released from the ribosome. The ribosome moves one codon step along the mRNA. The previous four steps are repeated until a termination sequence is reached, and the completed protein is released from the ribosome. In some cases, the protein undergoes posttranslational processing in which various chemical groups are attached to specific side chains and/or the protein is split into several smaller peptide chains. Copyright © McGraw Hill LLC. All rights reserved. No reproduction or distribution without the prior written consent of McGraw Hill LLC. 33  Figure3.3 All organelles have their own membranes © McGraw Hill, LLC 34  Figure 3.11 Rough and Smooth Endoplasmic Reticulum Rough endoplasmic reticulum Structure: Extensive membranous network of flattened sacs. Encloses a space that is continuous throughout the organelle and with the space between the two nuclear-envelope membranes. Has ribosomal particles attached to its cytosolic surface. Function: Proteins synthesized on the attached ribosomes enter the lumen of the reticulum from which they are ultimately distributed to other organelles or secreted from the cell. Smooth endoplasmic reticulum Structure: Highly branched tubular network that does not have attached ribosomes but may be continuous with the rough endoplasmic reticulum. Function: Contains enzymes for fatty acid and steroid synthesis. Stores and releases calcium, which controls various cell activities. Don W. Fawcett/Science Source Access the text alternative for slide images. © McGraw Hill, LLC 35  Figure 3.12 Golgi Apparatus Golgi apparatus Structure: Series of cup-shaped, closely apposed, flattened, membranous sacs; associated with numerous vesicles. Generally, a single Golgi apparatus is located in the central portion of a cell near its nucleus. Function: Concentrates, modifies, and sorts proteins arriving from the rough endoplasmic reticulum prior to their distribution, by way of the Golgi vesicles, to other organelles or to secretion from the cell. Biophoto Associates/Science Source Access the text alternative for slide images. © McGraw Hill, LLC 36  Figure 3.13 Mitochondrion Keith R. Porter/Science Source Mitochondrion Structure: Rod- or oval-shaped body surrounded by two membranes. Inner membrane folds into matrix of the mitochondrion, forming cristae. Function: Major site of ATP production, O2 utilization, and CO2 formation. Contains enzymes active in Krebs cycle and oxidative phosphorylation. Access the text alternative for slide images. © McGraw Hill, LLC 37  Figure 3.15 Cytoskeletal Filaments Associated with Cell Shape and Motility Cytoskeletal filaments Diameter Protein subunit (nanometer) Actin filament 7 G-actin Intermediate filament 10 Several proteins Microtubule 25 Tubulin © McGraw Hill, LLC 39  Summary Figure 3.3 Structures Found in Most Human Cells © McGraw Hill, LLC 40