Cell Structures and Functions Lecture Notes PDF

Cell Structures and functions  The Modern Cell Principle Advances in biology have expanded our knowledge of the cell. The modern cell principle incorporates our basic understanding of the genes and heredity and the collective works of scientists across disciplines. All organisms are compos...

Cell Structures and functions  The Modern Cell Principle Advances in biology have expanded our knowledge of the cell. The modern cell principle incorporates our basic understanding of the genes and heredity and the collective works of scientists across disciplines. All organisms are composed of cells and their cellular products. New cells arise from pre-existing cells. Chemical composition and metabolic activities are basically alike in all cells. Each cell is made of a protoplasm within a cell membrane.  The Modern Cell Principle Cells contain the hereditary unit of life. The growth of an organism involves the growth and multiplication of cells. Genetic pieces of information are stored and expressed inside the cell. Each cell maintains its individuality while having a specific internal environment and homeostasis.  CELL STRUCTURE All Cells have: an outermost plasma membrane genetic material in the form of DNA cytoplasm with ribosomes PLASMA MEMBRANE  CELL MEMBRANE AS FLUID AND MOSAIC MODEL The most abundant lipid component of the cell membrane, the phospholipids, and the membrane proteins are both amphipathic (having both a hydrophilic and a hydrophobic region).  CELL MEMBRANE AS FLUID AND MOSAIC MODEL The fluid mosaic model of the plasma membrane describes the plasma membrane as a fluid combination of phospholipids, cholesterol, and proteins. Carbohydrates attached to lipids (glycolipids) and to proteins (glycoproteins) extend from the outward facing surface of the membrane.  THE CELL MEMBRANE IS FLUID Cholesterol reduces membrane fluidity at moderate temperature but prevents solidification of membrane at low temperature THE CELL MEMBRANE IS MOSAIC ❖The cell membrane has proteins embedded in the lipid bilayer and each play specific functions. ❖There are three major types of membrane proteins: a. Integral proteins extend only into the hydrophobic core b. Peripheral proteins are loosely bound to the surface of the membrane; they are not embedded in the lipid bilayer c. transmembrane proteins are proteins that span the membrane. THE CELL MEMBRANE IS FLUID ❖ The cell membrane is not a rigid structure. ❖ Most of the phospholipids and some of the proteins embedded in it are shifting positions in the plane of the membrane. THE CELL MEMBRANE IS FLUID Kinks in the hydrocarbon tail prevent unsaturated fats from solidifying at room temperature. Saturated fats, which lack kinks, solidify at room temperature. GENETIC MATERIAL IN THE FORM OF DNA GENETIC MATERIAL IN THE FORM OF DNA Prokaryotes – no membrane around the DNA Eukaryotes – DNA is within a membrane  GENETIC MATERIAL IN THE FORM OF DNA Nucleotide – building block of DNA Three Parts: 1. Deoxyribose sugar 2. Phosphate group 3. Nitrogenous base STRUCTURE OF DNA Chargaff’s Rule states that in any organism’s genome, the amount of A= T and the amount of C = G COMPLEMENTARY BASE PAIRING CYTOPLASM WITH RIBOSOMES CYTOPLASM ❖Cytoplasm – fluid area enclosed by plasma membrane ❖Cytoplasm with ribosomes ❖Ribosomes – make proteins  CELL ORGANELLES Small membrane-bound compartments found inside the cells are called organelles. Found in the gel-like substance called cytoplasm. These organs perform specific functions. Processes of one organelle are necessary for function the function of another. NUCLEUS  STRUCTURE OF NUCLEUS Nuclear envelope Two phospholipid bilayers with protein lined pores Each pore is a ring of 8 proteins with an opening in the center of the ring Nucleoplasm – fluid of the nucleus  NUCLEUS ❖ largest organelle ❖ genetic information center or the control center of the cell ❖ surrounded by a nuclear membrane that forms a boundary between the nuclear contents (nucleoplasm) and the cytoplasm * The RNA leaves the nucleus and directs the synthesis of proteins in the cytoplasm  NUCLEAR MEMBRANE ❖The nuclear membrane or nuclear envelope is a highly regulated barrier consisting of two phospholipid bilayers. ❖ During cell division in higher eukaryotes, the nuclear membrane breaks down to allow microtubules to access the chromosomes. WHAT IS THE FUNCTION OF THE NUCLEAR PORE? Nuclear pores provide a passage for the exchange of substances between and nucleus and the cytoplasm. NUCLEOLUS  NUCLEOLUS (PL. NUCLEOLI) ❖ It is a round, basophilic structure located inside the nucleus. ❖This structure is not surrounded by a membrane and is usually present in cells that are at the interphase stage of the cell cycle. ❖In cells that are actively manufacturing proteins, more than one nucleolus per nucleus may be found. ❖ This nuclear structure is the ribosome-producing factory of the cell. Its main function is the synthesis of the ribosomal subunits (large and small subunits).  RIBOSOME ❖ site of protein synthesis  TYPES OF RIBOSOMES ❖Free ribosomes - those that are floating freely in the cytoplasm and manufacture proteins used exclusively by the cell. ❖ Attached ribosomes - those that are found on the surface of the membranes of the endoplasmic reticulum (ER)  ENDOMEMBRANE SYSTEM ❖Series of organelles responsible for: Modifying protein chains into their final form Synthesizing of lipids Packaging of fully modified proteins and lipids into vesicles for export or use in the cell  STRUCTURE OF THE ENDOMEMBRANE SYSTEM Endoplasmic Reticulum (ER) Continuous with the outer membrane of the nuclear envelope Two forms - smooth and rough Transport vesicles Golgi apparatus ENDOPLASMIC RETICULUM TYPES OF ENDOPLASMIC RETICULUM ❖ rough endoplasmic reticulum (RER) – characterized by the presence of ribosomes on its surface - Synthesis of proteins especially those that are destined to be secreted by the cell e.g. follicle-stimulating hormone ❖ smooth endoplasmic reticulum (SER) – has no ribosomes on its surface - Synthesis of lipids - Detoxification of drugs and poisons  FUNCTION OFRER ❖Proteins are modified as they move through the RER ❖Once modified, the proteins are packaged in transport vesicles for transport to the Golgi body GOLGI COMPLEX/APPARATUS  GOLGI APPARATUS ❖Made up of “dictyosomes” – stacks of flattened vesicles ❖For storage of fatty substances ❖Pinch off to vesicles ❖Involve in processing and packaging of secretory products that come through ER as secretory vesicles or granules, released by cell exocytosis.  GOLGI APPARATUS ❖The proteins and lipids are modified as they pass through layers of the Golgi ❖Molecular tags are added to the fully modified substances ▪These tags allow the substances to be sorted and packaged appropriately. ▪Tags also indicate where the substance is to be shipped TRANSPORT VESICLE  TRANSPORT VESICLES ❖Transport Vesicles Vesicle = small membrane bound sac ❖Transport modified proteins and lipids from the ER to the Golgi apparatus (and from Golgi to final destination ❖Vesicles store, transport, or digest cellular products and waste. The membrane enclosing the vesicle is similar to that of the plasma membrane, and vesicles can fuse with the plasma membrane to release their contents outside of the cell. ❖ Vesicles can also fuse with other organelles within the cell.  LYSOSOMES Tay-Sachs Disease occurs when the lysosome is missing the enzyme needed to digest a lipid found in nerve cells. As a result the lipid accumulates and nerve cells are damaged as the lysosome swells with undigested lipid Tay-Sachs Disease is a rare disorder passed from parents to child. It's caused by the absence of an enzyme that helps break down fatty substances. These fatty substances, called gangliosides, build up to toxic levels in the child's brain and affect the function of the nerve cells MITOCHONDRIA  MITOCHONDRIA STRUCTURE Two membranes Outer membrane Inner membrane - Highly folded Folds called cristae Matrix Intermembrane space (or outer compartment) DNA and ribosomes in matrix  MITOCHONDRIA Function – synthesis of Adenosine Triphosphate (ATP) Three major pathways involved in ATP production a. Glycolysis – cytoplasm b. Krebs Cycle – matrix c. Electron transport system (ETS) - intermembrane space MITOCHONDRIA In addition to the organelles mentioned a. the presence of the chloroplast that allows it to photosynthesize. The chloroplast contains the green pigment called chlorophyll that traps sunlight needed for the process of photosynthesis to happen. b. Presence of different types of plastids for storage of materials such as starch and pigments. c. An additional cell wall outside of the cell membrane to maintain internal turgidity and shape. In addition to the organelles mentioned d. The plant cell has a large vacuole, comprising almost 70- 80% of the cellular space to store water and prevent wilting of the plant e. Centrioles are absent in plant cells except those that are motile. f. Lysosomes are rare. g. Plasmodesmata are present. These are cellular junctions that allow cellular transport between adjacent plant cells  Plant Cell Wall Cellulose-based covering outside the cell membrane Cellulose composition differentiates the plants from the chitin-based cell wall of fungi and the peptidoglycan of bacteria This is composed of three layers: (primary wall, secondary walls, middle lamella)  Plant Cell Wall Middle lamella -First to be formed -Actually the outermost layer of the cell wall -Acts as cement of two adjacent cell walls -Once middle lamella is formed primary cell begins to form in either side -It includes cellulose, hemicellulose and pectin  Plant Cell Wall Secondary Wall -Thicker and stronger layer -Provide mechanical support -S2 has low microfibril angle -S1 and S3 have higher microfibril angles Xylan - found in the secondary wall xyloglucan - found in the primary cell wall Plastids Manufacture pigments that determine the color of the plant cell such as green in the case of the chloroplast Perform specialized functions in the plant cells. https://www.daviddarling.info/encyclopedia/C/chr omoplast.html Chloroplast Responsible for photosynthesis Absorb light and use water and carbon dioxide to produce food Abundant in the mesophyll layer of plant leaves Vary in shape among different plant species Member of plastids Discovered by Ernst Haeckel and defined by Andreas Franz Wilhelm Schimper  Chloroplast Photosynthesis happens in different parts of the chloroplast Thylakoid – light dependent -suspended in the stroma, contains chlorophyll Stroma – light independent - fluid part of chloroplast Chlorophyll – main photosynthetic https://flexbooks.ck12.org/cbook/ck-12-biology- pigment flexbook-2.0/section/2.19/primary/lesson/chloroplasts- bio/ Chloroplast Outer membrane is semi-porous covers the chloroplast Intermembrane space about 10-20 nanometers is present between the outer and inner membrane Inner membrane regulated passage of materials into the chloroplast, also responsible for manufacturing lipids and carotenoids Aside from chlorophyll other pigments called carotenoids absorb light Tomato (lycopene) Carrots (carotene) Corn (zeaxanthin) THANK YOU!!!