Lecture_3-3.pdf

Lecture 3: Cellular Anatomy Fall 2024 Textbook Sections: 4.1, 4.2, 4.3, 4.4, 4.5 Last class For the past lectures we have been examining how the molecular level of life is organized Today, we will see how these molecules form into cells. Polymer Synthesis Polymers...

Lecture 3: Cellular Anatomy Fall 2024 Textbook Sections: 4.1, 4.2, 4.3, 4.4, 4.5 Last class For the past lectures we have been examining how the molecular level of life is organized Today, we will see how these molecules form into cells. Polymer Synthesis Polymers are synthesized using a dehydration synthesis reaction Monomers can be recovered from polymers using a hydrolysis reaction  Hydrolysis and dehydration synthesis reactions are opposite reactions Levels of organization As we move up in levels of organization, the structures generated become significantly more complex. For instance, look at the difference between atoms and protein function…  Cells Before we learn how cells work we should learn what cells are… In biology, cells are described using what is known as cell theory Theories, in science, are defined as tested and confirmed explanations for observations or phenomena. They tend to be generated through inductive reasoning, where specific observations are used to establish general principles about phenomena. Theories are always open to critique, modification and dismissal based on new evidence Cell theory Cell theory contains three principles that apply, as far as we know, to all living things: 1. All living things are made of at least one cell 2. The cell is the fundamental unit of organization of life 3. All cells come from pre-existing cells Good cartoon recap: https://www.youtube.com/watch?v=4OpBylwH9DU Cell theory 1. All living things are made of at least on cell, and the life processes of metabolism and inheritance take place in these systems. Example: Organisms can either be multicellular (made of multiple cells) or unicellular (made of a single cell). Giardia lamblia Taenea solium is a is a unicellular multicellular parasite intestinal parasite  Cell theory 2. The cell is the fundamental unit of life Entities at the subcellular levels of organization (molecular or atomic) are not living. Some people might state that cells are the smallest living thing, but that statement has nothing to do with size. Rather, it is a statement made in connection with organization. As you will see cells come in a variety of sizes Cell theory 3. All cells come from pre-existing cells All cells arise from some form of cell division. In this course, the mechanisms of cell division we will examine are mitosis, meiosis and binary fission. Mitosis Meiosis Binary fission Cells Cells are quite small…but how small depends on the type of cell. Generally speaking, eukaryotic cells (plants, animals, fungi) are around 50𝛍m in diameter, prokaryotes (bacteria) vary between 1 and 10𝛍m 1𝛍m = 10-6 m https://learn.genetics.utah.edu/content/cells/scale/  Cells So we know that cells are small…why? It has to do with cell membranes… Plasma/cytoplasmic membranes control the rate for the exchange of materials (water, sugar, oxygen, …) between the cell and its environment Membranes are important for intake of nutrients, as well as export of waste Cells The larger cells grow, the smaller their surface area-to-volume ratio is This means that as a cell grows, it’s volume grows faster than its surface area Cells Who cares about all this….you do! If the surface area-to-volume ratio is small, it means there is less plasma membrane available for the transport of molecules, relative to the size of the cell… So for bigger cells it would be more difficult to transport molecules in and out of the cell Also it will be more difficult for substances within the cell to move throughout the cell, as its volume is very large Some cells are quite large, and overcome these problems witch speceific evolutionary adaptations (multiple nuclei, specific anatomy) Cells Fundamentally, all cells contain at least four structures: the plasma/cytoplasmic/cell membrane, the cytoplasm, centrally located genetic material and ribosomes Ribosome Plasma/cell/cytoplasmic membrane Made of a phospholipid bi-layer, that contains proteins, carbohydrates, and other lipids (more soon) Encloses the cell Allows for the transport of material in and out of the cell Allows for the interaction between the cell and its exterior Allows for cell to cell identification Cytoplasm Semifluid interior of the cell (75% water, 25% proteins/metabolites) Contains chemicals essential for cellular activity (sugars, fats, proteins,…) Specialized molecular machines, called organelles, are found there. Location of most of the chemical reactions that occur in the cell Liquid portion of the cytoplasm is called cytosol Centrally located genetic material Every cell contains DNA (deoxyribonucleic acid), the hereditary molecule In prokaryotes it is found in the central region known as the nucleoid In eukaryotes, it is found in the nucleus Ribosomes Protein factories of the cell Made of protein and ribosomal RNA (rRNA) (more in November) Use the code from messenger RNA (mRNA) and transfer RNA (tRNA) to synthesize proteins (more in November) Can be free or membrane bound Cell types There are two main types of cells: Prokaryotes and Eukaryotes The main and most important difference between the two cell types is the presence and absence of a nucleus. Prokaryotes DO NOT have a nucleus, while Eukaryotes DO!! Other, less important differences include the following: Prokaryotes tend to be smaller than Eukaryotes Prokaryotes are always unicellular organism while Eukaryotes can be uni- or multicellular All Prokaryotes have cell walls while not all Eukaryotes do  Prokaryotic cell structure Prokaryotes are a type of cell that include bacteria and archaea (rare form of prokaryote) Their typical structure always includes the following: Ribosomes: small organelles used for the synthesis of protein Nucleoid: region where DNA is found DNA/Chromosome: the actual genetic material of the cell Cytoplasm: interior of the cell Plasma membrane: contains the cell Cell wall: protects cell, maintains shape, helps prevent excess intake of water, made of peptidoglycan, in bacteria  Prokaryotic cell structure The following structures are also found in Prokaryotes, but are not found in all Prokaryotes: Capsule: jelly-like layer on the outside of cells that protects from predators and dehydration. Made of polysaccharides (aka sugars) Pili: Filament-like structures that allow for movement, attachment and exchange of genetic material Flagellum: used for “swimming”- like motility  Eukaryotic cell structure Eukaryotic cells are: Larger and more complex than the Prokaryotic cell Is compartmentalized by membrane bound organelles Possess membrane enclosed nuclei for the storage of DNA Can possess cell wall and flagella (depending on the cell type) Occur in animals, plants, fungi, and protists Plasma/cell/cytoplasmic membrane Made of a phospholipid bi-layer, that contains proteins, carbohydrates, and other lipids (more soon) Encloses the cell Allows for the transport of material in and out of the cell Allows for the interaction between the cell and its exterior Allows for cell to cell identification  Cytoplasm Semifluid interior of the cell (75% water, 25% proteins/metabolites) Contains chemicals essential for cellular activity (sugars, fats, proteins, ions, …) Specialized molecular machines, called organelles, are found there. Liquid portion of the cytoplasm is called cytosol Nucleus, Nucleolus, Nuclear Membrane, Nuclear Pore Nucleus: Filled with chromatin, loosely packed DNA, carries the majority of the genetic information within the cell. Nucleolus: Darker region of the nucleus, contains the genes necessary for the transcription of rRNAand production of ribosomes. Nucleus, Nucleolus, Nuclear Membrane, Nuclear Pore Nuclear envelope: Biological membrane that envelops and contains nuclear matter Nuclear pore: Pores in the nuclear membrane that allow the passage of material from the cytoplasm to the nucleus and vice-versa  Ribosomes Protein factories of the cell Made of protein and ribosomal RNA(rRNA) Use the code from messenger RNA (mRNA) and transfer RNA (tRNA) to synthesize proteins Can be free or membrane bound The Endomembrane System Comprised of the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysozomes, vacuoles, and microbodies (peroxisomes) Compartmentalizes the cell Responsible for molecular transport Provides surfaces for molecular synthesis of lipids and some proteins Rough Endoplasmic Reticulum Surface covered with ribosomes Site of protein synthesis Proteins synthesized here are destined for export from the cell, localization to vacuoles, lysosomes, or embedding in plasma membranes Site of protein glycosylation, modification by adding a carbohydrate to a protein Smooth Endoplasmic Reticulum No ribosomes Site of carbohydrate, steroid hormone, and lipid synthesis Stores and controls levels of intracellular (inside the cell) Calcium Site of cell detoxification through molecular modification of compounds Golgi Apparatus/Complex/Body Comprised of individual sacs called cisternae Functions in the collection, packaging, sorting and distribution of molecules within the cell or outside of it Molecules move from cis (facing nucleus) to trans (facing exterior of cell or plasma membrane) face Endomembrane System Lysosomes Arise from Golgi complex Contain digestive enzymes that can degrade proteins, lipids and carbohydrates at a rapid rate Used in defence against pathogens, and in breakdown of old organelles and cellular waste Microbodies Enzyme containing membrane bound vesicles Peroxisomes are an example of microbodies Contain oxidative enzymes that will produce hydrogen peroxide Involved in the breakdown of long chain fatty acids Vacuoles Found in both plants and some types of animal cells Surrounded by tonoplast (membrane) In plants: central vacuole Has channels for water exchange, controls tonicity of the cell (intracellular ion concentration)  Vacuoles There are many types of vacuoles They can be used for water storage and equilibrium Can store important molecules such as ions and nutrients As well they can store and segregate toxins and waste from the rest of the cell. Also found in fungi and protists Contractile vacuoles can control water balance by contracting and expanding Types and number of vacuoles present depend on the type of cell present Mitochondrion Metabolize sugar to produce ATP (more on this later this semester) Bacteria sized, contains own DNA and ribosomes with metabolism specific genes Chloroplasts Use the energy from sunlight to create sugar and ATP, found ONLY in plant/autotrophic cells Contain their own DNA and ribosomes  Cytoskeleton Series of protein fibres within the cell that support the cell shape and anchor organelles to fixed locations 3 different fibres: actin, microtubules and intermediate filaments  Actin filaments Also known as microfilaments Made of two long twisted fibres Involves in cellular movement, muscle contraction, and cellular division  Microtubules Largest component of the cytoskeleton Involved in cellular movement as well as movement of materials within the cell (think train tracks)  Intermediate filaments Diverse group of filaments, made of many different fibres Provide structural stability to cells  Centrioles Found only in animal cells Made of microtubule triplets, found in pairs in an area called the centrosome Plants and fungi have centrosomes, but no centrioles Allow for the assembly of microtubules, responsible for reorganization of microtubules during cell division  Cilia and flagella Made of microtubules, different than those found in prokaryotes Both can be used for motility (movement) Cilia resemble short hair-like projections and are used in some eukaryotes for the transports of material on the outside of the cell  Cell wall Hard, rigid structure that surrounds and protects the cell Has pores to allow communication between cells Allows for increased water intake Structurally different that those found in prokaryotes Made of the carbohydrates cellulose in plants, and chitin in fungi Homework Lab 1 due Cell practice packet due next week. Online quiz on Friday on cell structure