Eukaryotic Cell Structures PDF

Eukaryotic Cell PUBLIC / CYHOEDDUS Structures  PUBLIC / CYHOEDDUS Learning Outcomes Understand the organelle structures which exist in eukaryo...

Eukaryotic Cell PUBLIC / CYHOEDDUS Structures  PUBLIC / CYHOEDDUS Learning Outcomes Understand the organelle structures which exist in eukaryote cells Explain the structure, role and function of the nucleus Explain the structure, role and function of the ribosomes Explain the structure, role and function of the endomembrane system Explain how mitochondria and chloroplast structure allows them to produce energy for the cell Explain the components of the cytoskeleton network, the components they are made of and how this contributes to cellular function  PUBLIC / CYHOEDDUS Modern Cell Theory All living things are made of cells Different forms in different organisms Can have specialist functions The cell is the smallest living unit of structure and function of all organisms DNA and RNA – hereditary information Manufacture of new molecules Use organic molecules as energy sources = cellular metabolism  PUBLIC / CYHOEDDUS Eukaryotic and prokaryotic cell - similarities DNA Ribosomes Cytoplasm Cell Membranes  PUBLIC / CYHOEDDUS Eukaryotic and prokaryotic cell - differences  PUBLIC / CYHOEDDUS Compartmentalisation of activities Allows all enzymes and compounds necessary for a process to be localised and concentrated Eukaryotic cells sub-divide specific tasks into membrane bound compartments (organelles) Now need to be an active and organised transport system throughout the cell Allows cells to differentiate and specialise in specific tasks Increasingly important in multicellular organisms which have dedicated structures/organs for performing specific tasks  PUBLIC / CYHOEDDUS Membrane bound organelles Derived from membrane In eukaryotes – organise functions within the cell Nucleus Ribosomes Endomembrane system  PUBLIC / CYHOEDDUS Eukaryotic nucleus Is surrounded by the nuclear envelope Envelope is a double membrane Nuclear matrix maintains shape Insoluble fibrous network Nuclear pores – complex protein channels within the membrane Allow regulated movement of biomolecules e.g. proteins into the nucleus Nucleoplasm – liquid phase around the nucleus Mostly occupied by chromatin DNA is arranged in chromosomes and associated with several protein regulation molecules Nucleolus – makes ribosomal RNA (rRNA) Can have more than one – number corresponds to protein synthesis Forms and combines with proteins to from ribosome subunits  PUBLIC / CYHOEDDUS The endomembrane system Purpose: create, modify and export cell products e.g. proteins and lipids Inter-related internal membranous sacs Composed of:- Nuclear envelope Rough endoplasmic reticulum Smooth endoplasmic reticulum Golgi apparatus Several types of vesicles and lysosomes  PUBLIC / CYHOEDDUS Ribosomes Organelle that performs translation (protein synthesis) Catalase the formation of peptide bonds Consists of 2 subunits Small (40S) subunit which binds mRNA Large (60S) subunit which catalyses peptide bond formation Provide an interface for mRNA and aminoacyl tRNAs. Ribosome has 3 tRNA binding sites P (peptidyl) site A (aminoacyl) site E (exit) site  PUBLIC / CYHOEDDUS Endoplasmic reticulum – Rough ER Ribosome studded membrane Translate mRNA and forms new peptides as they pass through into the lumen of the ER Folded to increase surface area Extensive inter-connected network of membranous channels and vesicles called cisternae Each cisternae surrounds and enclosed space – ER lumen Makes secretory proteins Chemically cleaves off signalling sequences Addition of carbohydrate units  PUBLIC / CYHOEDDUS Endoplasmic reticulum – Smooth ER Purpose: Production and metabolism of lipids and steroid hormones Calcium storage Detoxification of drugs and toxins Smooth and rough ER can be connected in a continuous network  PUBLIC / CYHOEDDUS Golgi complex Purpose: Major sorting compartment for protein traffic within the cell Compartment between protein creation and secretion Stack of flattened, membranous sacs without ribosomes Located between the RER and the plasma membrane Receives proteins from the ER, transported by vesicles Can further modify proteins (e.g. removal of amino acid chains) Proteins are sorted and transported to other cellular locations or secreted  PUBLIC / CYHOEDDUS Secretory vesicles Vesicles will have membrane recognisable signals Allows for fusion of membranes Rupture of membrane allows content release  PUBLIC / CYHOEDDUS Lysosomes and Peroxisome Lysosomes Hydrolytic enzymes – at least 50 Can fuse with an incoming vesicle e.g. bacterial cell taken up by phagocytosis Lysosome breaks down the vesicle and the bacterial cell wall within Peroxisome Filled with digestive enzymes such as peroxidase Metabolise nitrogen containing compounds Remove toxic lipids Converts peroxide to water and oxygen  PUBLIC / CYHOEDDUS Energy and Eukaryotes  PUBLIC / CYHOEDDUS ATP – the energy currency of the cell Most important form of chemical energy in all cells in any organism Energy rich molecule with high phosphoryl transfer potential ATP-ADP cycle – fundamental mode of energy exchange in biological systems Principle immediate donor of free energy not long term storage Consumed within minutes of formation  PUBLIC / CYHOEDDUS Mitochondria Membrane organelles within which cellular respiration occurs Consist of:- Outer membrane Inner membrane which is folded (cristae) Matrix Contain a small circular piece of mitochondrial DNA  PUBLIC / CYHOEDDUS Chloroplasts – plant cells! Has its own genome Similar to mitochondria Have an outer and inner membrane with an inner compartment – STROMA Stroma is like the mitochondrial matrix Within the stroma is another membrane system  thylakoids In higher plants, thylakoids are stacked grana  PUBLIC / CYHOEDDUS Cytoskeletal Network Comprised of a number of different structures 1. Microtubules 2. Microfilaments 3. Intermediate filaments Used for a number of processes 1. Structural stability – maintenance of cell shape 2. Internal transport of molecules 3. Cellular movement 4. Contraction of skeletal muscle  PUBLIC / CYHOEDDUS Principles of cytoskeletal architecture Cytoskeleton is made of small subunits that polymerise This enables the cell to make and break structures quickly and easily Addition of subunits confers polarity onto the cytoskeleton  PUBLIC / CYHOEDDUS Microtubules Subunits Alpha tubulin Beta tubulin Polarity: Yes – plus and minus end Diameter: 25nm Functions: Organisation of cell shape and polarity Intracellular transport of vesicles and organelles Chromosome movements  PUBLIC / CYHOEDDUS Centrosome Nucleation of microtubules is the limiting factor in their development Microtubules of the cytoskeleton are nucleated by the centrosome Contains two barrel-shaped centrioles 0.2 microns in diameter Contains proteins that assist in the formation of a closed microtubule  PUBLIC / CYHOEDDUS Role of microtubules 1) Organisation of cell shape and polarity  PUBLIC / CYHOEDDUS Role of microtubules 2) Intracellular transport of vesicles and organelles  PUBLIC / CYHOEDDUS Role of microtubules 3) Chromosome movements  PUBLIC / CYHOEDDUS Microfilaments Subunits G- actin monomer Polarity: Yes – plus and minus end Diameter: 7nm Functions: Cell locomotion Cytokinesis Muscle contraction Maintenance of cell shape Intracellular transport  PUBLIC / CYHOEDDUS Role of microfilaments 1) Maintenance of cell shape  PUBLIC / CYHOEDDUS Actin protrusions Produce lamellipodia and filopodia protrusions based on actin polymerisation Cross-linked actin in bundles by actin-binding proteins Filopodia – slender cytoplasmic projections from the leading edge of lamellipodia in migrating cells  PUBLIC / CYHOEDDUS Role of microfilaments 2) Cell locomotion  PUBLIC / CYHOEDDUS Intermediate filaments Subunits: Dimer Multiple proteins Polarity: None known Diameter: 8 -12nm Functions: Structural support Maintenance of cell shape Nuclear lamina  PUBLIC / CYHOEDDUS Four classes of intermediate filaments Keratin Epithelial cells for strength Vimentin and vimentin related Vimentin: Connective tissue for shape Desmin: Muscle cells for structural support Neurofilaments Nuclear lamins All cells – provides nuclear scaffold  PUBLIC / CYHOEDDUS Disorders of Intermediate Filaments-Keratin Filaments There are 54 functional keratin genes! Each is specialised, sometimes they go wrong. e.g. Epidermolysis bullosa Group of genetic conditions that result in easy blistering of the skin and mucous membranes, Can be fatal. Genetic condition - Mutations in the genes encoding keratin filaments disrupts the tensile strength of skin cells Defects in attachment between or within layers of the skin KRT5 and KRT14 gene mutations.  PUBLIC / CYHOEDDUS Disorders of the Nuclear Lamina: Progeria Extremely rare genetic disorder. Symptoms resemble aging at a very early age. Mutated gene product (progerin), break down more easily, not properly incorporated into the nuclear lamina. Unable to provide adequate structural support, causing an abnormal shape. Limits ability for cell to divide.  PUBLIC / Summary CYHOEDDUS Eukaryotic Cells have a ‘skeleton’ This gives eukaryotic cells structural integrity Contains different types of tubules and filaments. Allows cells to be predators!  PUBLIC / CYHOEDDUS The rest of the module……