Cell Biology1. 1 Introduction to Cells Cell Theory >> According to the cell theory, living organisms are composed of cells. The cell theory states that cells are basic unit structure and function of every living thing. The three main ideas include: 1. Cells are the building blocks of structure in living things 2. They are the smallest unit of life 3. Cells are formed from one another, pre-existing cells by division 4. Cells also store all information they require for growth, development and behavior 5. Cells are the location for all the chemical reactions needed for life, metabolism. Common Cell Features Surrounding cell membrane, that separates the contents of the cell from its external environment. Genetic material which store’s instructions for the cell’s activities. Activities are chemical reactions, catalysed by enzymes made in the cells Cell’s activities are powered by their own energy release system. Exceptions to the Cell Theory >> Looking for trends and discrepancies: although most organisms conform to the cell theory, there are exceptions There are some tissues and organisms that are not made of typical cells: Skeletal Muscle It is made up of muscle fibres. Like cells these fibres are enclosed inside a membrane, They are much larger than most cells (300 or more mm long) Contain hundreds of nuclei. like structures called hyphae. Aseptate Fungi Consists of thread. .Obtaining food for energy and material.To remove waste products of metabolism Homeostasis .Giant Algae Such as Acetabularia Can grow to a length of as much as 100mm We can expect them to consist of many small cells They only contain a single nucleus so are not multicellular. They are long undivided sections of hypha. Unicellular organisms carry out seven functions of life Nutrition . These hyphae are not divided into sub-units containing single nucleus.Chemical reactions inside the cell to release energy Growth .Producing offspring either sexually or asexually Many unicellular organisms have a method of movement. Structure of unicellular organisms is more complex than most cells.Keeping organism’s internal environment constant Reproduction . Unicellular Organisms >> Organisms consisting of only one cell carry out all functions of life in that cell.Irreversible increase in size Response . needed for growth Metabolism . in multicellular organisms. which contain many nuclei. but some remain in a fixed position or merely drift in water or air currents.Ability to react to changes in the environment Excretion . but not by the same amount. As the size of a structure increases. All organisms need to exchange substances such as food. . the surface area to volume ratio decreases. cells are very small so that they are able to exchange substances efficiently >> Multicellular organisms have properties that emerge from the interaction of their cellular components.Size of Cells 1nm – a 10nm – 100nm – 1000nm – 10000nm (100µm) 1cm 10^-2m 1mm 10^-3m 1µm 10^-6m 1nm 10^-9m centimete r milimeter micromet er nanomete r molecule cell membrane virus Bacterium (1µm) – Organelles (10µm) 100000nm – Cells Actual Size = Size of image / Magnification >> Surface area to volume ratio is important in the limitation of cell size. For example. tissues. using a cube: Length Surface Area Volume SA:V As organisms get bigger. larger organisms have a slower rate of exchange (diffusion/radiation) with their outside surroundings. This is true for organelles. cells. gases and heat with their surroundings. a variety of algae.g. Some unicellular organisms live together in colonies. Volvox aureus. As a result. For this reason. organs and organisms. waste. their volume and surface area both get bigger. E. The rate of exchange of substances depends on the surface area of the organism which is in contact with its surroundings. The characteristics of the whole organism. including the fact that it is alive. Multicellular organisms form tissues. The whole is greater than the sum of its parts. known as emergent properties.They’re able to develop the ideal structure. Organisms consisting of a single mass of cells.g the function of the red blood cell is to carry oxygen and the function of the rod cell in the retina is to absorb light and transmit impulses to the brain. . fused together. . They’re a group of cells combine which together to specialize and perform the same function. >> Specialized tissues can develop by cell differentiation in multicellular organisms. Individual cells in a group can organize themselves and interact with each other to form a living organism with distinct overall properties. Each cell has a unique and specific role.This allows them to be more efficient . with the enzymes needed to carry out the chemical reactions This ability of cells to develop different ways of carrying out specific/specialized functions is called differentiation. When the component parts of a complex structure interact. emergent properties arise. e. The human body has many specialized cells. are multicellular. It also makes stem cells suitable for therapeutic uses.The cells can become specialized to perform their function. etc. or express. 2 Ultrastructure of Cells Prokaryotic Cell Structure >> Prokaryotes have a simple cell structure without compartmentalization Prokaryotes were the first organisms to evolve on this earth and have the simplest cell structure Functions of Prokaryotic Cells( Bacteria Cells) . functions and adaptations with that cell. Stem cells are not fully differentiated. the cells are capable of dividing many times to produce large amounts of tissue. Movement of nutrients.Stem cells can divide again and again to produce high quantities of new cells. because all adult tissue stems from them. At early stages in embryonic development. The name stem cells was given to the zygote and the cells of the early embryo in the 19th century. Multicellular organisms are large and need to have specialized parts to their structure so that all the necessary functions of life can be performed. Stem cells have two key properties: . Specialization in multicellular organisms is more efficient for organisms competing for a specific resource. They are also extremely versatile and can differentiate along different pathways into any of the cell types found in a new animal. particular genes that correlate with these specific functions. The expression of these genes will influence the shapes. 1. a muscle cell will only express muscle genes. For example. They are useful for tissue growth or replacement of lost or damaged cells. These cells switch on. so they can differentiate in different ways to produce different cell types. Differentiation . water.>> Differentiation involves the expression of some genes and not others in a cell’s genome. can happen faster and more effectively than passing between cells through diffusion. but not nerve cell genes. >> The capacity of stem cells to divide and differentiate along different pathways is necessary in embryonic development. Nucleoid: Storage of genetic information. This is where DNA is replicated and copied out to form mRNA.Ribosomes(70S): protein builders of the cell.rER (Rough Endoplasmic Reticulum): Contains ribosomes. . .Nucleus: Contains the chromosomes consisting of DNA. . Uncoiled chromosomes (chromatin) are spread throughout.Golgi apparatus: Processes proteins brought in vesicles from the rER for transport within the cell .Pili: assists in attaching to other surfaces..Flagella: helps the cell move around.Cell Wall: strengthens and maintains the structure of the cell .Plasma Membrane: regulates movements of materials into and out of the cell . ribosomes.Cytoplasm: Contains DNA. which can be used to break down ingested food or break down organelles. allowing mobility Eukaryotic Cell Structure >> Eukaryotes have compartmentalized cell structure Functions of Eukaryotic Cells . the site of DNA replication. . which is important for genetic DNA transfer . and organic compounds needed to carry out life processes.Lysosomes: Contains digestive enzymes. where protein synthesis occurs . Synthesizes proteins for the secretion from the cell . . which grow to full size and divide again. Centrioles: Contains microtubules. in the form of enzymes. if given right condition. Vesicles are small vacuoles that transport materials inside the cell.- - - - - - It’s important for cell defence. This is asexual reproduction. attaching itself to the plasma membrane cell elongates to separate chromosomes membrane folds in. releasing it into the cytoplasm. Produces glucose and other organic compounds by photosynthesis. Also digests fat if being used by the cell for energy. Ribosomes(80S): Synthesize proteins. The cell will divide into two cells. The bacterial cells are replicated. Chloroplasts: Contain the pigment. Cell division in prokaryotes >> Prokaryotes divide by binary fission. digestion of harmful organisms/chemicals Mitochondria: Produces energy in the form of ATP for cell by aerobic respiration. which move chromosomes during cell division. The The The The DNA is first replicated. can multiply rapidly by binary fission. Vesicles: A single membrane that contains fluid inside. Centriole forms an anchor point for microtubules during cell division. Cilia/Fagella: Both used for locomotion. Constructed in the nucleolus. pulling itself together in the middle cell then splits into two daughter cells The resolution of electron microscopes >> Electron microscopes have a much higher resolution than light microscopes. In this process the cell is replicated to form two identical daughter cells. Prokaryotes. chlorophyll used in photosynthesis. which is 200 nanometers. Therefore. Beams of electrons have a shorter wavelength.2µm. The resolution of modern electron microscopes is 0. Electron microscopes therefore have a 200x better resolution than light microscopes. therefore that electron microscopes have a higher resolution. If the resolution is made any higher. the maximum magnification with a light microscope is 400x. While light microscopes reveal the structure of cells. The maximum resolution of a light microscope is about 0. electron microscopes reveal the ultrastructure. The resolution cannot be higher as it is limited by the wavelength of light (400-700 nm). the image is blurry.001µm or 1nm. Making separate parts of an object distinguishable by eye is called resolution. . The two fatty acid tails. There are two parts to the molecule: one. composed of hydrocarbon chains are hydrophobic. o The phosphate head is hydrophilic. which is attracted to water (hydrophilic) and the other part that isn’t attracted to water (hydrophobic). .1. they naturally arrange into a bilayer position with the hydrophilic heads are facing the water and the hydrophobic tails are facing inwards away from the water.3 Membrane Structure Fluid Mosaic Membrane Structure >> Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules Phospholipids are in the structure of every cellular membrane o Phospholipid molecules are amphipathic. o When phospholipids mix with water. The phospholipid bilayer consists of integral proteins. which catalyze reactions in the cytoplasm. o Integral Proteins: Span from one side of the phospholipid bilayer to the other. They are also involved in other cell substance recognition as in the immune system. which is part of the immune system. Often slide and collide with each other. though never flip or change sides.e ATP maltase) Electron Carriers: These are a chain of peripheral and integral proteins that allow electrons to pass across the membrane. Enzymes: Integral proteins in the membrane may be enzymes (i. Within these are passive and active membrane pumps. glycoproteins and cholesterol. peripheral proteins. o Glycoproteins: Involved in cell recognition. Can also act as receptors in cell signaling. They are involved in maintaining the cell shape or motility. They only allow specific ions through Receptor Protein: These detect hormones arriving at cells to signal changes in function. position in the membrane and function Channel Protein: They span the membrane. Active pumps use ATP to move specific substances across the membrane. . o Cholesterol: Binds together lipid in the plasma membrane reducing it’s fluidity o >> Membrane proteins are diverse in terms of structure. They are involved in transporting substances across the membrane o Peripheral Proteins: Placed on the surface of the membrane. They can be enzymes. allowing movement of large molecules across.The attraction of the hydrophobic tail in the center keeps the membrane stable. as a result of the random motion of particles. osmosis and active transport Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration.4 Membrane Transport >> Particles move across membranes by simple diffusion. They will diffuse quickly via this route.>> Cholesterol is a component of animal cell membranes Cholesterol is a component of animal cell membranes. 1. or the pore. as it offers little resistance. so cholesterol fits between phospholipids in the membrane. Simple Diffusion: The molecules are small. as well as oxygen and carbon dioxide. hence diffusion through the membrane must be restricted. . Diffusion occurs because more particles move from the area of higher concentration to an area of lower concentration. it is permeable to non-polar substances. These have complex shapes. as well as lipid molecules Facilitated diffusion: For larger molecules. It acts as a shield against the non-charged regions of the membrane for the molecule. one end is hydrophilic. Most of cholesterol molecule is hydrophobic. Diffusion through a cell membrane will occur if the membrane is fully permeable to the solute. but there is no control over the direction of movement. This is important as animal cells need to maintain concentration differences of these ions across membranes. In the case of the phospholipid bilayer. hence they can simply pass through the phospholipid molecules of the membrane. Cholesterol restricts movement of phospholipid molecules Reduces fluidity of the membrane Reduces permeability of the membrane to hydrophilic particles such as H2 ions. such glycerol. which provide a channel through the protein. there are channel proteins to take the through the membrane. Examples include O₂ and CO₂. These channels only allow a specific type of substance through. facilitated diffusion. o E. Active transport can move substances against concentration gradient – from a region of lower to a region of higher concentration Protein pumps in the membrane are used for active transport. so cells can control what is absorbed and what is expelled. Each pump only transports particular substances. across a partially permeable membrane. Osmosis is the passive movement of water molecules from a region of low water concentration to a region of high water concentration. Pumps work in a specific direction – the . Simple and facilitated diffusion are passive movements that require no energy.g chloride channels allow only chlorine ions to pass through Passive movement means that no energy (ATP) is used for the movement of molecules from one side of the membrane to the other. Attraction between solute particles and water molecules are the reason for water moving to regions with a higher solute concentration Active Transport is the movement of substances across membranes using energy from ATP. >> The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis.substance can only enter the pump on one side and can only exit on the other. the pump is modified to create electrochemical phenomena. . o They are called active because they need energy to function o This energy causes the shape of the protein. Vesicles move materials within cells. allowing it to move the molecule across the membrane Sodium Potassium pump creates an electro-chemical gradient across the membrane of all cells. In nerve cells. The inside of the cell has a negative charge compared to outside. They can then move the contents through the cytoplasm. The continuity of the plasma membrane is not disrupted.The fluidity of membranes allows them to move and change shape. The nucleus of a eukaryotic cell can divide from two genetically identical nuclei by a process called mitosis. The vesicle fuses with plasma membrane.6 Cell Division The Role of Mitosis Mitosis is division of the nucleus into two genetically identical daughter nuclei. Mitosis allows the cell to divide itself into two daughter cells. Each chromosome is converted from a single DNA molecule into two identical DNA molecules called Chromatids. then breaks off. Small pieces of the membrane can be pinched off the plasma membrane to create a vesicle containing some material from outside the cell. Before mitosis can occur all of the DNA nucleus must be replicated. . Part of the membrane is pulled inwards and a droplet of fluid is enclosed when it’s pinched off. During mitosis one of these chromatids passes to each daughter nucleus. Exocytosis: The vesicle membrane fuses with the plasma membrane. and its contents are secreted. and its contents are expelled. This happens during Interphase the period before mitosis. 1. Endocytosis: A vesicle is formed when the plasma membrane in folds. This is endocytosis. for example vesicles move proteins from the rough ER to the Golgi apparatus. each with one of the nuclei and therefore genetically identical to the other. Vesicles move materials within the cell. The cell will replicates its centrosome. growth. It consists of 3 phases: . tissue repair and asexual reproduction. which is important for the movement of chromosomes.Mitosis is involved whenever cells with genetically identical nuclei are required in eukaryotes: during embryonic development. Although mitosis is a continuous process cytologists have divided the events into four phases Prophase Metaphase Anaphase Telophase Interphase This is when the DNA is replicated. S Phase: The synthesis phase. There is all the activity of growing a cell.G1 Phase: The cytoplasm is still active. Microtubules in the cytoplasm start from a spindle. so that after mitosis both the new cells have a complete set of genes. when the DNA is replicated. The mass of the DNA in the cell doubles. Some do not progress beyond G1 because they are never going to divide so do not need to prepare for mitosis. This is called supercoiling. In plant cells the same structure is formed. preparing for cell division to take place. The cell replicates all the genetic materials in its nucleus. G2 Phase: The third stage. the cell continues with normal functions such as protein synthesis. At the end of prophase the nuclear membrane breaks down. Microtubules grow from the structures called Microtubule Organising Centres (MTOC) to form a spindle shape array that links the poles of the cell. mitochondria replication or cholorplast replication. when there is further growth of the cell. All the chromosomes are copied and form chromatids. These attach to the centromeres and are arranged at the equator of the spindle. They enter a phase called G0. but without the presence of centrioles. These remain attached until they divide in mitosis. Prophase The chromosomes become shorter and flatter by coiling. To become short enough they have to coil repeatedly. The nucleolus breaks down. Metaphase The centrioles move to opposite ends of the cell. which may be temporary or permanent. . Radiating out of the centrioles. The nucleolus reforms. the normal repressed state of mitosis is disrupted by mutation to the proto. Interphase then follows the division of cytoplasm. the spindle fibers shorten and the chromatids are pulled by the centromere to the opposite poles. In plant cells a new cell is formed across the equator of the cell. the cells begin to . One cell of each of the four stages of mitosis is identified right. Mitochondria and cytoplasm increase as they grow and divide In plant cells. This divides the cell into two. the chloroplasts increase in the same way Uncontrollable Cell Division o o Tumors. It occurs after mitosis. reactions like cell respiration also occur during cell division. In animal cells the plasma membrane at the equator is pulled inwards until it meets in the centre of the cell. A high index indicates a fast growing tumour. and is different in plant and animal cells. Once separated. but DNA replication in the nucleus and protein synthesis in the cytoplasm happen during interphase. The begin to decondense and become chromatin again. Telophase The nuclear membrane reforms around both groups of chromosomes at the opposite ends of the cell. Anaphase The centromeres divide. they are referred to as chromosomes. are cell mass formed as a result of uncontrolled cell division. As a result. mitotic index = number of cells in mitosis / total number of cells Cell Cycle in Eukaryotes The cell cycle is the sequence of events between one cell division and the next. or cancers. Mitotic Index Is the ratio between the number of cells in mitosis in a tissue and the total number of observed cells. In a tumor. with plasma membrane on both sides. Interphase: very active in the life of a cell when many metabolic reactions occur. It has two phases: interphase and cell division.oncogene. dividing it in two. Cytokinesis The division of the cytoplasm to form two cells. They can occur in any tissue. gamma rays. healthy cells. two of the tumor suppressor... Eventually they take over the surrounding. . Some cells may break away and form a secondary tumor elsewhere. some chemicals (tar in tobacco smoke) as well as virus infections. eroding blood vessels).o o o o o divide uncontrollably. The cells form an irregular mass of cells.). The damage to the DNA can result from ionizing radiation (X-rays. resulting in the loss of control of cell division. The accumulation of mistakes in DNA causes cancer. The proto-oncogene mutates into the oncogene. the protein that stops the copying of damaged DNA. The development of cancer requires at least two mutations. one of the proto-oncogene. which can lead to malfunction and death. Another cause is damage to the gene that codes for p53. the tumor. Some factors are also inherited. which is why it is more common in older people. It is caused by damage to DNA chromosomes. replacing normal functioning cells (such as replacing blood forming cells in the bone marrow or the heart muscles so that the heart fails). Cancer exerts its deleterious effect on the body by destroying the adjacent tissues (such as compressing nerves.