Cell Organelles PDF

# CELL, DEVELOPMANT ## 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 c...

# CELL, DEVELOPMANT ## 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 than 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: - **A. Single membrane bound organelle**: Large vacuoles, ER, Golgi apparatus, lysosomes, secretory vesicles. - **B. Double membrane bound organelles**: 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 the 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. - Where ribosomes found attached on rough ER synthesis proteins that are transported to Golgi body. - 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 + 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 lysosomes being isolated within a membrane. - The enzymes in lysosomes are synthesized on rough endoplasmic reticulum transported to Golgi body, the Golgi vesicle containing the processed enzymes later on bud off and called primary lysosome (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, (70S 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. - **Notice**: - Number of mitochondria in cells vary according to the activity of the cell and their energy demand. - **Example**: liver cells contains about 2000 mitochondria For more aerobic respiration and ATP production Which exit to the cell through the outer mitochondrial membrane. - To be used in: - Synthesis of cholesterol, glycogen, proteins, biological molecules - Intra cellular movement of vesicles - Exocytosis. - Active transport - If you exercise regularly, your muscles will make more mitochondria. - **The endosymbiont theory**: - Mitochondria and chloroplast were thought to be originally symbiotic eubacteria (prokaryote) that were engulfed by eukaryotic cells, as they have 70S ribosomes and circular DNA molecules. - mitochondria are the result of endocytosis of aerobic bacteria - chloroplasts are the result of endocytosis of photosynthetic bacteria ### Centrioles: - **1. They are non-membranous organelles.** - **2. Found in animal cell but not plant cell.** - **3. 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. ### 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 site of light-dependent reaction in photosynthesis. - Stroma is the site of light independent reaction of photosynthesis. - **Overall function of chloroplast**: Site of photosynthesis. - **Comparison between Chloroplast and 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 take place. - **Chloroplast**: Has stroma. - **Mitochondria**: Has matrix