Cell Organelles - 7-20 PDF

# CELL, DEVELOPMENT DIVERSITY AND CONSERVATION ## 1. Cell organelles and their functions: ### 1- Fractionation of the cell: - This is done by using centrifuge, where the more rotation of the centrifuge per minute, the more the ability to separate smaller particles. - It is u...

# CELL, DEVELOPMENT DIVERSITY AND CONSERVATION ## 1. Cell organelles and their functions: ### 1- Fractionation of the cell: - This is done by using centrifuge, where the more rotation of the centrifuge per minute, the more the ability to separate smaller particles. - It is used to separate cell structures by their relative density, larger cell structure has greater density and sink further down the centrifuge tube. ### 2- using radioactive labelled chemical substances - Providing cells with radioactively labelled chemical substances that are building blocks for specific modules and then find out where they appear in the cell. - **Example:** using labelled amino acids to observe the synthesis of proteins. The introduction of radioactively labelled amino acids into a growing culture of cells involved in protein synthesis is an experiment undertaken to trace the pathway taken by secreted proteins. - Ribosomes then RER then Golgi apparatus then plasma membrane. - The labelled product can be tracked using microscopy or using centrifuge, where parts of cell can be separated out and the radioactively labelled substances can be identified ## B Structure and functions of cell organelles: - The cell structures are divided into 2 groups: - **1. MEMBRANOUS ORGANELLES** - These are organelles which are separated from cytoplasm by their membranes to have optimum pH and specific function (i.e their activities can be separated from their surrounding cytoplasm) - **Example:** localise enzymes in reaction pathways as respiration in mitochondria and photosynthesis in chloroplast. - Also keep biological molecules separate such as hydrolytic enzymes in lysosomes - **They include:** - Large vacuoles - ER - Golgi apparatus - lysosomes - secretory vesicles - Nucleus - Mitochondria - chloroplast - Amyloplast - **2. NON-MEMBRANOUS ORGANELLE:** - **They include:** - Ribosomes - starch grains - glycogen granules - cilia - centrosomes - flagella - nucleolus ### 1. ENDOPLASMIC RETICULUM - It is a membrane bound organelle. - Its membrane is connected to the outer membrane of nuclear envelope. - The membrane forms an extended system of flattened compartments (sacs) or tubular called cisternae. - **There are two types:** - **ROUGH ER** - It is covered with many ribosomes (SoS) - **Function:** - Protein/ polypeptide synthesis by its ribosomes. which is site of Translation. - Modification of protein polypeptide chains become folded in the RER. - Polypeptides packed into vesicles to be transported to Golgi apparatus. - **Role of RER in transport of proteins:** - Proteins made in ribosomes attached to rough ER enter the sac (cisternal space) and move through them. - The proteins are then modified (ex; folding polypeptides) - Small sacs called shuttle vesicles can break/bud off from the ER and these can join together to form the Golgi body. - **SMOOTH ER** - **Function:** - Lots of SER found in liver for Synthesis of lipids such as cholesterol and also in testes and ovaries for the synthesis of the reproductive steroid hormones oestrogen and testosterone. - **Description:** - Membranous with vesicles budding off. - Tubular with cisternae (not flattened) - Fluid filled sacs - And not associated with ribosomes. ## 2. ribosome - **Function:** - Site of translation and protein synthesis. - **A.** Where ribosomes found attached on rough ER synthesis proteins that are transported to Golgi body. - **B.** While ribosomes found free in cytoplasm synthesis proteins used inside the cell for intracellular use. - **Description:** - They are small non membranous organelles. - Made up of two subunits: large and small subunit. - Each unit is made of rRNA and protein. - Ribosomes are made in nucleolus. - **There are two types of ribosomes:** - **70 S** which are small (18 nm) and found in prokaryotes, Mitochondria and chloroplast (30S and 50S subunits with ratio rRNA to proteins 2:1) - **80 S** ribosomes (25nm) found in eukaryotes free in cytoplasm as well as attached to the outside of the rough ER (made up of 40S and 60S subunits. With ratio of RNA to proteins is 1:1) ## Golgi apparatus - **Description** - Appears as a stalk of flattened membrane bounded sacs and cisternae curved shaped). - with no connection between membranes. - surrounded by secretory vesicles at the end of the sac - The stack is being constantly formed at one end (Forming Face) from fusion of vesicles which bud off from the ER and are broken down again at the other end (maturing face) to form Golgi vesicles that can move to the cell membrane to empty its content to the exterior of cell by exocytosis. - The stack of (sacs + associated vesicles) is referred to as Golgi apparatus/ complex. - **Function** - Golgi apparatus collect, process and allow chemical modification of proteins **Example:** By adding carbohydrate to make glycoproteins (such a mucus) in a process known as glycosylation - Also allow chemical modification of lipids. - They allow packaging and transporting of the synthesised proteins and lipids in Golgi vesicles, either to other parts of the cell or secreted out of the cell. - Production of Golgi/ secretory vesicles( which transport proteins& lipids) and lysosomes( which contains storage of hydrolytic enzymes) ## Lysosomes - **Description** - They exist in nearly all animal cells. - Dark spherical sac ( a form of a vesicle) surrounded by a single membrane and with no internal structure. - **Function:** - They contain hydrolytic enzymes such as proteases, lipase and carry out digestion of: - Excess or worn-out organelles or cells. - Food particles in simple organisms. - Engulfed viruses/ bacteria to digest and destroy them) - The rest of the cell is therefore protected from these enzymes by lysosome being isolated within a membrane. - The enzymes in lysosomes are synthesised on rough endoplasmic reticulum transported to Golgi body, the Golgi vesicle containing the processed enzymes later on bud off and called primary lysosome I so they are made and bud off Golgi apparatus) ## Mitochondria - **Structure and adaptation** - Usually, it's about 1 micrometre in diameter - Double membrane bound organelle. - Rod shaped for shorter distance for easier pumping of ATP molecules produced by mitochondria - Inner membrane: is folded forming cristae, function is to increase surface available to carry more ATP synthase for aerobic respiration to produce more ATP. - Outer membrane is more permeable - Inter membrane space : is the space between the 2 membranes, which a fluid space. - Matrix: interior solution containing circular DNA, .(70 S ribosomes, to allow mitochondria to synthesis their own proteins and to replicate independently, also contain stalked particles. - **Function:** - site of aerobic respiration (in matrix solution and the inner membrane [cristae]) Producing ATP molecules - Involved in lipid synthesis. ## Centrioles - **They are non-membranous organelles** - **Found in animal cell but not plant cell.** - **Centrioles are hollow cylinders but formed of 9 groups of microtubules, each in triplets** - The 2 centrioles lie close together at right angle to one another in a region called as centrosome found near the nucleus of animal cell. - **Function:** - During nuclear division, they replicate at interphase ( just before prophase), then move to poles and act as microtubule organising centre( MTOC). i.e they organise microtubules. - To assemble/formation of spindle fibres (in prophase). - To separate the chromosomes/chromatids. - Also modified centrioles are found elsewhere as flagella and cilia. ## Nucleus - **Description (structural adaptation)** - Largest cell organelle of 1-20 micrometre) It is a double membrane bounded organelle, spherical in shape. - These 2 surrounding membranes known as nuclear envelope. - The outer membrane of nuclear envelope is continuous with the membrane of rough ER and has 80S ribosomes attached. - The nuclear envelope has nuclear pores which control the exchange of materials between nucleus and cytoplasm. - Inside nuclear envelope, mainly nucleic acid (DNA and RNA) and proteins. - **Example:** - The exist of mRNA and ribosomes, the entrance of proteins help to make ribosomes, nucleotides, ATP, and some hormones as T3(thyroid hormone) - **Function** - The whole nucleus controls all cell activities because it contains 'chromatins (DNA bonded to protein when cell is not actively dividing) which carry genes thus responsible for controlling cell division, activities and inheritance. - The nuclear DNA carries instructions (genes) for synthesis of proteins. - mRNA is produced in nucleus. - Nucleolus is responsible for the synthesis of ribosomal RNA and combine it with proteins to form incomplete ribosome (makes ribosomal subunits). ### Notice: Plant cells included all the previous organelles except for centrioles & lysosomes. And the coming organelles are only found in plant cells. ## GRANA AND THYLAKOID, CHLOROPLAST - **Structure and adaptation** - It is about 4-10 micrometre in diameter - 2-3 micrometre in thickness. - So can be seen and measured by light microscope - Found only in plant cells - Biconvex shape with Double membrane bound organelle. - The 2 membranes form chloroplast envelope. - Large inner folded membrane to increase surface area where enzymes controlled reaction takes place. - Inside the chloroplast there is additional membranous system consisting of: - a- Thylakoid: disc shaped cavities, having their membrane carrying chlorophyll and enzymes. - b- Grana: stacks of thylakoids (only seen by electron microscope) - C- Inter granal lamellae: membrane connecting between Grana. - d- Stroma: interior fluid which contains loop of DNA, starch grains, 70S ribosomes and enzymes, lipid droplets. - **Function:** - Thylakoid is the the site of light dependent reaction in photosynthesis. - Stroma is the site of light independent reaction of photosynthesis. - Overall function of chloroplast: Site of photosynthesis ## Chloroplast, Mitochondria - **Both are large organelles.** - **Both are biconvex in shape.** - **Both contain their own loop of DNA** - **Both contain 70S ribosomes.** - **Both surrounded by outer membrane(double membrane bound organelles)** - **Both are thought to be prokaryotic organelles engulfed by other cells and become part of these cells(endosymbiont theory).** - **Both have enormous folded membrane Increasing surface area where enzymes controlled reactions takes place.** - **Has stroma Chlorophyl in thylakoid** - **Has matrix** ## Large permanent vacuole - **Description:** it occupies 80% of the total Plant cell. It is a sap-filled sac (containing water, ions, minerals and sugars) surrounded by a single membrane called tonoplast which controls exchange between cytoplasm and vacuole, allowing movement of substances in and out by osmosis. - **Function:** - It gives turgidity to plant cell by building up turgor pressure on cell wall. - Act as food storage by storing water, ions, minerals and sugars. - Stores cell sap which helps keeping continuous osmosis of water. - Stores waste products, Eventually, those waste products would be sent out of the cell. - **Notice** that vacuole contain pigments, so upon heating, changes in the characteristics of the membrane of vacuole, so causes pigment to leak out. ## PLASMODESMATA - **Description** - Cytoplasmic bridge/ no cell wall at all. - Allow communication between cells. - Allow movement of water by symplastic pathway. - Lined with cell membrane. ## Amyloplast - **Description** - Double membrane bound organelle. - Colourless and store starch (amylose and amylopectin). - Found in parts of plant with high amount of starch stored (potato tuber) - Stores concentric layers of amylopectin. ### Notice - Both chloroplast and mitochondria share 70S ribosomes, circular DNA, double membrane bound organelles. - Differences between bacteria and mitochondria is that mitochondria has no cell wall, no cytoplasm instead has matrix, has no flagella nor slimy capsules, also mitochondria has cristae but bacteria have mesosomes. - Photosynthetic prokaryotes have no chloroplast. - **organelles seen by light microscope:** - Nucleus - cell wall - cell membrane - vacuole - chloroplast - Mitochondria (with no details) - Nucleoli - **organelles only seen by electron microscope:** - lysosomes - centrioles - Ribosomes - ER - Golgi body - chloroplast Grana - + all organelles seen by light microscope. ## Prokaryotic cells - Average diameter of cell from 0.5-5 micrometre (very small) - Circular DNA free in cytoplasm with no nucleus/ loop of DNA (non linear chromosome) - Naked DNA - Has only 70s ribosomes (18 nm) - No ER - Have fewer cell organelles (no membrane bound organelles) - No double membrane- bound organelles Such as mitochondria and chloroplast - No single membrane- bound organelles such as Golgi body, lysosomes, vacuoles - Cell wall made of peptidoglycan (murein) - Has plasmids - Has slime capsule (for protection from antibodies, antibiotics, WBCs, phagocytes and prevent dehydration), and pili (allow bacteria to adhere to surfaces). ## Eukaryotic cells - Up to 40 µm Chave ranging diameter from 10-100µm) larger - DNA found as chromosomes inside nucleus ( linear) - Notice: protoplasm is the cytoplasm and nucleus combined. - DNA associated with histone proteins - Has both 70s and 80 ribosomes - ER present to which ribosomes may be attached. - Has many types of cell organelles - Has a double membrane- bound organelles Such as nucleus, mitochondria and chloroplast - has single membrane -bound organelles Such as Golgi body, lysosome, vacuoles. ## ultrastructure of prokaryotic cells: - **Structure** - **1. Bacterial cell wall** - Have a layer of peptidoglycan (murein) consisting of parallel chains of polysaccharide cross linked by short peptides producing an enormous molecules with, a net like structure. - **2. Capsule (slime layer):** - Present in some bacteria. - Present around their cell wall. - Produced from starch, gelatin, protein or glycolipid. - **3. Pili and flagella:** - **Pili:** thread-like protein projections found on surface of some bacteria. - **Flagella:** made from a many stranded helix/ helices of the contractile protein flagellin, and found in some bacteria. - **function** - **1.** Prevents the cell swelling and bursting. - **2.** Maintains shape of bacterium, giving support and protection to the contents of the cell. - **1.** Protects the bacteria from phagocytosis by white blood cells. - **2.** Also cover the cell markers on cell membrane that identify the cell, making it easier for bacterium to be pathogenic without being easily identified by the immune system. - **3.** Also help bacteria survive dry conditions. - **Used for attachment of bacteria to host cell and involved in sexual reproduction 1.** - **Needed to move bacteria by rapid rotations( about 100 Revolution per second**