Anatomy of the Cell PDF

Anatomy of the Cell Learning outcomes: 1. Describe composition of membranes, and their role in enclosing the cell and in establishing compartments within the cell 2. Describe the basic morphology and function of the nucleus and cell organ...

Anatomy of the Cell Learning outcomes: 1. Describe composition of membranes, and their role in enclosing the cell and in establishing compartments within the cell 2. Describe the basic morphology and function of the nucleus and cell organelles 3. Describe the cytoskeleton helps to maintain cell shape and integrity and leads to cell locomotion and contraction 4. Describe intercellular junctions in providing tissue integrity and in cell- to-cell communication Anatomy of the cell: The cell is the basic structural unit of all living organisms. Anatomy of the cell What are the features common to a eukaryotic cell? outer membrane inner cytosol: contain proteins, carbohydrates, electrolytes and carbohydrates a cytoskeleton made of thin and intermediate filaments Anatomy of the Cell 1  membrane bound organelles inside cytosol Inclusions(structures within cytoplasm which can be found by membrane) Components of eukaryotic cells Eukaryote: any cell or organism that possesses a clearly defined nucleus Eukaryotic cells have an outer membrane, an inner cytosol , a cytoskeleton, membrane bound organelles and other structures called inclusions Anatomy of the Cell 2  Plasmalemma (outer membrane) Separates cytoplasm from outside environment, forming a selectively permeable barrier Bimolecular layer of amphipathic phospholipid molecules (phospholipid bilayer) Hydrophilic heads at outer and inner surfaces Hydrophobic tails at centre Contains integral proteins→ include receptors, channels, transporters, enzymes and cell attachment proteins Can exocytose(out of cell) and endocytose (into cell) material Anatomy of the Cell 3  The cell membrane is: →Fluid Can change shape easily Membrane proteins can diffuse laterally in CM many proteins are anchored so not distributed fairly across the PM →Selectively permeable Highly permeable to small hydrophobic molecules permeable to water, oxygen Virtually impermeable to charged ions(PM repels these because of charge or hydration of ion) Interior of a cell cytoplasm contains organelles and inclusions( see picture below) Anatomy of the Cell 4  Summary of organelles: Organelles are intracellular organs that each have a specific function and structural organization. In the CYTOPLASM: Mitochondria: energy production RER: protein synthesis Anatomy of the Cell 5  SER: cholesterol and lipid synthesis/detoxification Golgi-Apparatus(GA): modification and packaging of secretions Lysosomes: hydrolytic enzymes for intracellular digestion Nucleus: contains genetic code Can also be found in Cytoplasm: Inclusions: represent components that have been synthesises by the cell itself (pigment glycogen stores, lipid droplets, pre-secretion product) or taken up from the extracellular environment (endocytotic vesicle) Inclusions are dispensable and can be present as transients Name an example of inclusions? → Adipose cells in brown fat Cytoskeleton Anatomy of the Cell 6  A network of proteins within the cell that determines the shape and fluidity of the cell →Allows movement of organelles and of the cell itself →Gives shape and can change shape Microfilaments: composed of 2 actin(protein) strands dynamic cytoskeletal element Involved in cellular movement, cell division and muscle contraction 7nm Intermediate filaments: 6 proteins that bind intracellular elements together and to the plasma membrane more than 50 types glial fibrillary acidic protein that can be found in humans filaments form a network throughout the cytoplasm Gives strength to structure of cell >10nm These classes are used in pathology to identify tumour origins Anatomy of the Cell 7  Microtubules: composed of ⍺ and β tubulin which form protofilaments which form microtubule Originate from centrosome, polar, dynein and kinesin attach and move along them 25nm important for cilia,flagella and mitotic spindle can be assembled and disassembled include microtubule associated proteins(MAPS) Dynein and kinesin ‘drag’ the membrane of organelles (e.g. the GA) and vesicles along the microtubule Kinesin is an ATPase that moves toward the cell periphery Dynein is an ATPase that moves toward the cell centre Used for long axonal processes and other processes that take long to move along the cell Cytosol Solution of proteins, electrolytes and carbohydrates which the cellular components are embedded Nucleus Enclosed by a nuclear envelope Surrounded by a double nuclear membrane (composed of inner and outer nuclear membrane) have nuclear pores that provide continuity with cytoplasm outer nuclear memebrane is studded with ribosomes, and continous with rough ER Anatomy of the Cell 8  Contains chromosomes Euchromatin: DNA that is more dispersed and undergoing transcription Heterochromatin: DNA that is highly condensed and not undergoing transcription Nucleus is surrounded by a double nuclear membrane Site of RNA synthesis mRNA and tRNA in nucleus rRNA in nucleolus(within nucleus) Nuclear envelope Encloses nucleus Inner and outer nuclear membrane with the perinuclear cistern in the middle Outer nuclear membrane is studded with ribosomes Nuclear pores: allow the transport of molecules across the nuclear envelope Ribosomes Formed in nucleolus important for protein synthesis Small subunit binds RNA, large subunit catalyses peptide bond formation export of ribosomes depends on nuclear pore complex Endoplasmic reticulum (means net like structure) Anatomy of the Cell 9  RER: studded with ribosomes, responsible for protein synthesis and initiation of glycoprotein formation ER: forms a network of interconnecting memebrane bound compartments in cell SER: involved in continuous processing of proteins from RER and lipid synthesis important for synthesis of lipids most cells have small amounts of SER Cells that sythesize steroid hormones have a lot of SER → The amount of r present determines how active the cell is. Rough endoplasmic reticulum Golgi apparatus Composed of a group of flattened, membrane bound cisternae Golgi cisterns function in modification and packaging of macromolecules synthesised in ER: - add sugar - Cleaves some proteins - sorts macromolecules into vesicles Transport vesicles arrive at Golgi from SER; Golgi modifies and packages them Mitochondria: Anatomy of the Cell 10  Oblong, cylindrical organelles They are composed of an outer and an inner membrane The inner membrane is extensively folded to form cristae→ which act to increase the available surface area Power generators of the cell (generate ATP via oxidative phosphorylation and involved in the synthesis of certain lipids and proteins) Contain their own DNA and system for protein production Intracellular junctions Basically things that connect cells to other cells into a functional unit, mainly in epithelial cells →Only between immobile cells → 3 types Anatomy of the Cell 11  Occluding (tight) Links cells to form a diffusion barrier and prevents diffusion Water tight seal to prevent water flowing between cells (bladder/kidney) also known as zonula occludens Anchoring Provides mechanical strength “cells adhere to one another” Adherens junction: anchors cells together & prevents separation Desmosomes: link sub membrane intermediate filaments of adjacent cells (macula adherens) desmosomes are common in the skin, where they provide mechanical stability also called zonula adherens cadherin molecules bind to each other in extracellular space and link molecules to actin of the cytoskeleton Anatomy of the Cell 12  Communicating (gap) Allow movement of molecules between cells (selective diffusion- like a tunnel) Sort of like sky bridges that connect 2 adjacent buildings each junction is studded with several pores, these pores are produced by connexon proteins Made up of connexins (transmembrane proteins) which allows ions and cytokines to pass between cells→ allows rapid communication can be found in epithelia but also in smooth muscle and cardiac muscle(critical for spread of excitation) Anatomy of the Cell 13  Junctional complex: close association of several types of junctions found in certain epithelial tissues Cellular transport Material can move across the cell membrane via diffusion, transport proteins (pumps or channels) or by incorporation into vesicles (requires ATP) Vesicular transport: Endocytosis: material from the extracellular space can be incorporated into the cell. Membrane invaginates (turns inside out), fuses, newly made endocytic vesicle buds into cell Often receptor mediated Exocytosis: works in reverse to endocytosis Phagocytosis: bacteria binds to cell surface, cell engulfs it to form phagosome, binds with lysosome containing digestive enzymes producing a phagolysosome Anatomy of the Cell 14