General Zoology (1) Lecture 4 - 2024-2025 PDF

GENERAL ZOOLOGY (1) | (Lecture 4) Dr. R.A (2023 – 2024) GENERAL ZOOLOGY (1) | (Lecture 4)  2 General Zoology (1) - Lecture 4 Non-Membranous Organelles (Non-Membranous Structures): 1) Ribosome: Location:...

GENERAL ZOOLOGY (1) | (Lecture 4) Dr. R.A (2023 – 2024) GENERAL ZOOLOGY (1) | (Lecture 4)  2 General Zoology (1) - Lecture 4 Non-Membranous Organelles (Non-Membranous Structures): 1) Ribosome: Location: ▪ Ribosomes are found in both prokaryotic and eukaryotic cells. ▪ In eukaryotic cells, ribosomes are found in cytoplasm, mitochondria and chloroplast. NOTE: ribosomes found in prokaryotes are generally smaller than those in eukaryotes. General Function: ▪ Ribosome is a complicated “micro-machine for protein synthesis”. ▪ There are about 10 billion protein molecules in a mammalian cells and ribosomes produce all of them. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  3 General Structure: ▪ Ribosomes are formed from 2 ribosomal subunits: a) Large ribosomal subunit. b) Small ribosomal subunit. NOTE: two subunits are unequal in size (i.e., large subunit is about twice as large as the small subunit) and exist in free state (not attached) until required for use. Molecular Structure: ▪ Eukaryotic ribosome is composed of both nucleic acids and proteins. ▪ About two-thirds of its mass is composed of ribosomal RNA (rRNA) and one-third of about 50 different ribosomal proteins. Ribosomal Synthesis: ▪ Proteins and nucleic acids (rRNA) that form the ribosomal subunits are made in the nucleolus and exported through nuclear pores into the cytoplasm. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  4 Prokaryotic Ribosomes VS Eukaryotic Ribosomes: a) In prokaryotes, ribosomes are made up from three rRNA molecules. b) In eukaryotes ribosomes are made up from four rRNA molecules. ▪ Mass units of ribosomes are Svedberg (S) values, which are based on how rapidly the subunits settle to the bottom of test tubes under the centripetal force of a centrifuge. NOTE: ribosomes of eukaryotic cells have Svedberg values of 80S, while prokaryotes have 70S ribosomes. Types of Ribosomes in Animal Cell: a) Free ribosome: function in a free state in the cytoplasm (i.e., floating freely throughout the cell and not attached to a membrane). ▪ Function: synthesis proteins that are utilized within the cell itself only. b) Attached ribosome: settle on endoplasmic reticulum to form rough endoplasmic reticulum (i.e., attached to endoplasmic reticulum membrane). ▪ Function: synthesis proteins for intracellular or extracellular usage by the cell. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  5 NOTE: location of ribosome in a cell determines what kind of protein it makes. NOTE: When many ribosomal subunits admit an mRNA molecule as soon as the mRNA emerges from the nucleus, they form a structure called polysome. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  6 Function of Ribosomal Subunits in Protein Synthesis: a) Small ribosomal subunit mainly a decoding function. ▪ The smaller unit links up with mRNA and then locks-on to a larger sub-unit. b) Large ribosomal subunit has mainly a catalytic function (i.e., catalyze formation of peptide bonds between amino acids). ▪ In large subunit, ribosomal RNA performs the function of an enzyme. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  7 NOTE: ribosomal subunits are not static units (i.e., not always attached to each other). When production of a specific protein has finished, the two subunits are separated (i.e., ribosomal subunit assembly have a temporary existence). Large Ribosomal Subunits Sites: ▪ Large ribosomal subunit has 3 sites for association with transfer RNA molecules (tRNA): 1) A (aminoacyl) site. 2) P (peptidyl) site. 3) E (exit) site. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  8 NOTE: The surfaces of the two ribosomal subunits that face one another contain the binding sites for mRNA and incoming tRNAs and, thus, are of key importance for the function of the ribosome. NOTE: The active site, where amino acids are covalently linked to one another, also consists of RNA. This catalytic portion of the large subunit resides in a deep cleft, which protects the newly formed peptide bond from hydrolysis by the aqueous solvent. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  9 2) Cytoskeleton: Introduction: ▪ In 1903, Nikolai Koltsov proposed that the shape of cells is determined by a network of tubules that he termed the “cytoskeleton”. ▪ The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells. It extends from the cell nucleus to the cell membrane and is composed of similar proteins in various organisms. ▪ In eukaryotes, it is composed of three main types: a) Microfilaments. b) Intermediate filaments. c) Microtubules. ▪ All these types are capable of rapid growth (assembly) or disassembly dependent on the cell's requirements. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  10 General Functions of Cytoskeleton: 1) Provide structural support: maintain cell shape and resilience to tension and stress. 2) Intracellular transport of vesicle and movement of mRNA (e.g., from ER to Golgi apparatus to Plasma membrane) and translocation of organelles (i.e., position various organelles within the cell). 3) The cytoskeletons also function as apparatus for cell motility in single- cell animals by crawling movement by pseudopodia on a substratum (e.g., Amoeba) or swimming in aqueous medium through cilia or flagellar movement (e.g., Paramecium). Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  11 4) Motility in multicellular organism: the contraction of muscles, movement of sperms, WBC and phagocytes. 5) It forms the most essential component of cell division machinery. Cytoskeletons are responsible for the alignment and separation of chromatids and subsequent cytokinesis to form daughter cell. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  12 a) Microfilament (Actin Filament): Structure of microfilament: ▪ Microfilaments also known as actin filaments are solid rods of protein. ▪ They are called actin filament because they composed of actin protein. ▪ Size: the diameter of filament is about 7 nm, and they are the smallest cytoskeletal filaments. ▪ They occur in almost all eukaryotic cells. ▪ Their structure is two strands of actin wound in a spiral shape. ▪ It is synthesized as a single polypeptide consisting of 375 amino acids. ▪ Monomers: individual actin molecules are referred as G-actin (Globular actin). ▪ The G-actin molecule polymerize to form microfilament which is called as F-actin (Filamentous actin). Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  13 Actin Polymerization steps: a) Nucleation (Initial phase in actin polymerization): ▪ G-actin (actin monomers) bind to ATP forming ATP-bound actin monomers, which is hydrolyzed to ADP following filament assembly. ▪ In nucleation step, ATP-bound actin monomers aggregate into short oligomer (consisting of 3 actin monomers) called nuclei. NOTE: ATP-bound actin monomers in nucleation stage is also called G-actin. b) Elongation (Filament assembly): ▪ The nuclei elongate rapidly by adding ATP-Actin monomers from both ends. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  14 c) Stationary state and Steady state: ▪ After the formation of nuclei, ATP-bound actin elongates to become filamentous actin (F-actin) with positive and negative ends (stationary state). ▪ ATP-bound actin molecule hydrolyzes to form ADP-bound actin at the negative end. ▪ Stable F-actin in steady state is stabilized in by addition of: i. Tropomodulin capping protein in the negative (-) end to stop depolymerization (i.e., prevents disassembly of ADP-bound actin molecules). Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  15 ii. Cap Z capping protein in the positive (+) end to stop polymerization (i.e., prevents assembly of ATP-bound actin molecules). Function of microfilaments (actin filaments): 1) Membrane endocytosis during phagocytosis. 2) Locomotion in unicellular organism (endoplasmic streaming in Amoeba to form pseudopodia). 3) Muscle Contraction (sliding of actin filament over myosin filaments). 4) Cytokinesis during cell division. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  16 b) Intermediate Filament: Function of Intermediate Filament: ▪ Structural support of the cell. It is a flexible, tough and extensible filament that is found only in animal cells. Structure of Intermediate Filament: ▪ Size: the diameter of the intermediate filaments is 10-12 nm. ▪ Monomers: 70 different fibrous protein subunits. Monomers of intermediate filaments proteins are classified according to their distribution in specific tissues: i. In nucleus (e.g., nuclear Lamin A, B, and C). ii. In skin epithelium (e.g., acidic and basic keratins). Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  17 Intermediate Filament (IF) Assembly: 1) The first stage of filament assembly is the formation of dimers in which the central rod domains of two monomer polypeptide chains wrap around each other in a coiled-coil structure. 2) Two of these coiled-coil dimers (running in opposite directions), associate to form a staggered antiparallel tetramer. 3) Tetramers assemble side by side to form protofilaments. 4) The final intermediate filament contains eight protofilaments wound around each other in a rope-like structure. NOTE: In contrast to actin filaments and microtubules, intermediate filaments are apolar (i.e., they do not have distinct plus and minus ends). Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  18 Function of Intermediate Filament: 1) Membrane mechanical support. 2) In cytosol, they form internal framework that supports the cell and add resilience of the cell. 3) They form the connecting network for cell attachment to their extra cellular matrix (ECM) through hemi-desmosomes and cell-cell adhesion through desmosomes. 4) They form the interconnecting link between cytoskeletons. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  19 NOTE: intermediate filaments are similar to an anchor for the cell. c) Microtubules: Structure of Microtubules: ▪ Microtubules are stiff, hollow, unbranched and inextensible tube found in all eukaryotes. ▪ Size: The diameter of the microtubule fiber is 25 nm. ▪ Monomers: GTP-αβ tubulin heterodimers as protein subunits. NOTE: addition of tubulin incorporation is on the Beta tubulin end (plus end). Function of Microtubules: 1) Intracellular transport (e.g., vesicle transport along the ER - GA – PM axis and moving organelles throughout the cytoplasm). Tubulins are associated with Kinesin and dynein motor proteins. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  20 2) They are the major components of cilia and flagella. 3) Participate in the formation of spindle fibers and in movement of chromosomes during mitotic division. Assembly of Microtubules: 1) Formation of microtubule occurs through 2 stages of nucleation and elongation in the MTOC: 1) Nucleation: free αβ-tubulins dimmers aggregate to form short filaments called protofilaments. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  21 2) Protofilament associates into lateral sheets with the addition of more tubulin dimer monomers. 3) The sheet conformation is unstable, hence, they wrap around to form circular tube with 13 protofilaments. NOTE: free αβ-tubulins are GTP-bounded in β-subunit, which is hydrolyzed after incorporation. 4) Kinesin and dynein motor proteins are associated with tubulins. NOTE: Motor proteins are responsible for transport or translocation of organelles, vesicles on the microtubule along tracks of microtubules. Cilia and Flagella: Cilia and flagella are projections from the cell. They are made up of microtubules and are covered by an extension of the plasma membrane. They are motile and designed either to: a) Move the cell itself. b) Move substances around the cell. ▪ The primary purpose of cilia in mammalian cells is to move fluid, mucous over their surface. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  22 Cilia and flagella have the same internal structure, the major difference is in their length and number. Cilia and Flagella Structure: ▪ Cilium is composed of internal core of microtubules called axoneme. On cross-sectional view, it contains nine pairs of microtubules (doublets) surrounding two central microtubules. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  23 ▪ The microtubules composing each doublet are composed of two types of microtubules: 1) A microtubule. o Each microtubule A exhibits a pair of “arms” that contain a motor protein called dynein. o Function: dynein arms have ATPase activity. In the presence of ATP, they enable the tubules to slide along one another so the cilium can bend. 2) B microtubule. o The protein “nexin” permanently links the microtubule A with the microtubule B of adjacent doublets. ▪ Each of the nine doublets give rise to radial spokes, toward the two central microtubules. o Function: because of the nexin and radial spokes, the doublets are held in place, so sliding is limited lengthwise. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  24 Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  25 Basal body: It is composed of: 1) 9 + 0 arrangement of triplet microtubules (i.e., A- tubules, B- tubules, and C-tubules) at the proximal end of the basal body. 2) a transition zone that is composed of a 9 + 0 arrangement of doublet microtubules. 3) The distal end of the mature basal body is capped by a basal plate and is followed by a classical 9 + 2 microtubule axoneme. Centrosome: Location: ▪ Found only in animal cells, near the nucleus. Structure: ▪ Centrosome consists of 2 centrioles located at right angles (perpendicular) to each other. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  26 ▪ Each centriole is made of nine triplets of microtubules arranged in a ring. Function: 1) play a role in cell division. 2) They have a role in building cilia and flagella, during which time they are referred to as basal bodies. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  27 Lecture (4) - Homework Questions!! A. Choose the correct answer: 1) Which of the following organelles is best describes as a ribonucleoprotein complex: a) Centrosome. b) Lysosome. c) Ribosome. d) Peroxisome. 2) Eukaryotic ribosome is made up of: a) Two rRNA molecules. b) Three rRNA molecules. c) Four rRNA molecules. d) Five rRNA molecules. 3) ribosomes of prokaryotic cells have Svedberg values of: a) 50S. b) 60S. c) 70S. d) 80S. 4) When many ribosomal subunits admit mRNA molecules they are best described as: a) Free ribosomes. b) Attached ribosomes. c) Polysomes. d) All of the above. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  28 5) Which of the following is true regarding ribosomes: a) Large subunits have a decoding function. b) Small subunits have a catalytic function. c) Ribosomal assembly have a temporary existence. d) Large subunits have 3 sites for association with mRNA. 6) ……………… is a complex network of interlinking protein filaments present in the cytoplasm. a) Microfilaments. b) Intermediate filaments. c) Microtubules. d) All of the above. 7) Which of the following is not true regarding actin Polymerization: a) In nucleation, ADP-bound actin monomers aggregate into short oligomer called nuclei. b) In elongation, nuclei elongate rapidly by adding ATP- actin monomers to the plus end only. c) In steady state, tropomodulin is added to the in the plus end to stop polymerization. d) All of the above. 8) From the function of actin filaments: a) Formation of desmosomes. b) Formation of spindle fibers. c) Formation of cilia. d) Formation of pseudopodia. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  29 9) ……………… consists of 70 different fibrous protein monomers. a) Microfilaments. b) Intermediate filaments. c) Microtubules. d) All of the above. 10) Nuclear lamina is as example of: a) Microfilaments. b) Intermediate filaments. c) Microtubules. d) All of the above. 11) Intermediate filament contains ……………… wound around each other in a rope-like structure. a) Two protofilaments. b) Four protofilaments. c) Six protofilaments. d) Eight protofilaments. 12) ……………… are apolar filaments: a) Microfilaments. b) Intermediate filaments. c) Microtubules. d) All of the above. 13) From the functions of intermediate filaments: a) Membrane endocytosis. b) Muscle Contraction. c) Cytokinesis during mitotic division. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  30 d) Add resilience to the cell. 14) ……………… act as an anchor for the cell. a) Microfilaments. b) Intermediate filaments. c) Microtubules. d) All of the above. 15) ……………… are hollow, unbranched and inextensible tubes found in all eukaryotes. a) Microfilaments. b) Intermediate filaments. c) Microtubules. d) All of the above. 16) The diameter of microtubules is: a) 7 nm. b) 10 nm. c) 25 nm. d) None of the above. 17) ……………… consists of GTP-αβ tubulin heterodimer protein subunits. a) Microfilaments. b) Intermediate filaments. c) Microtubules. d) All of the above. 18) ……………… are associated with Kinesin and dynein motor proteins for intracellular transport of vesicles and organelles. a) Microfilaments. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  31 b) Intermediate filaments. c) Microtubules. d) All of the above. 19) From the functions of microtubules: a) Formation of cytoplasmic tracks. b) Formation of sperm tail. c) Formation of spindle fibers. d) All of the above. 20) Microtubules consists of: a) 10 Protofilaments. b) 11 Protofilaments. c) 12 Protofilaments. d) 13 Protofilaments. 21) Which of the following is true regarding microtubules: a) Free αβ-tubulins are GDP-bounded in α-subunit. b) Free αβ-tubulins are GTP-bounded in α-subunit. c) Free αβ-tubulins are GDP-bounded in β-subunit. d) Free αβ-tubulins are GTP-bounded in β-subunit. 22) Axoneme system of cilia consists of: a) Nine doublets of microtubules with two central ones. b) Nine doublets of microtubules without two central ones. c) Nine triples of microtubules with two central ones. d) Nine triples of microtubules without two central ones. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  32 23) In cilia, microtubule A contains a motor protein called: a) Kinesin. b) Dynein. c) Nexin. d) Radial spoke. 24) The proximal end of the basal body consists of: a) 9 + 0 arrangement of doublet microtubules. b) 9 + 0 arrangement of triplet microtubules. c) 9 + 2 arrangement of doublet microtubules. d) 9 + 2 arrangement of doublet microtubules. 25) Which of the following is not true regarding centrioles: a) Each centriole is made of nine triplets of microtubules arranged in a ring. b) Centrosome consists of 2 centrioles located perpendicular to each other. c) Together with basal body they form the microtubule organizing center (MTOC). d) None of the above. Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  33 Lecture (4) - “Model Answer” A. Choose the correct answer: 1) C 2) C 3) C 4) C 5) C 6) D 7) D 8) D 9) B 10) B 11) D 12) B 13) D 14) B 15) C 16) C 17) C 18) C 19) D 20) D 21) D 22) A Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)  34 23) B 24) B 25) D Dr. R.A (2024 – 2025) GENERAL ZOOLOGY (1) | (Lecture 4)