Cell Structure and Functions PDF

ANATOMY AND PHYSIOLOGY OF CELL Structure and function of cells Dr LSK  Cell Structure Structure of cells: ANATOMY Functions of cells: PHYSIOLOGY Cell Injury and Repair: PATHOPHYSIOLOGY  STRUCTURE OF A TYPICAL HUMAN CELL Cells are the building b...

ANATOMY AND PHYSIOLOGY OF CELL Structure and function of cells Dr LSK  Cell Structure Structure of cells: ANATOMY Functions of cells: PHYSIOLOGY Cell Injury and Repair: PATHOPHYSIOLOGY  STRUCTURE OF A TYPICAL HUMAN CELL Cells are the building blocks of tissues and organs. They are the smallest functional unit found in our bodies. cells tissues organs systems Each human cell consists of a plasma membrane. Inside the plasma membrane, is the cytoplasm. Suspended within the cytoplasm are tiny organs called organelles. There are several different organelles, including the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes and centrioles. Each organelle has a specialised and individual function.  THE CELL (PLASMA) MEMBRANE  It consists of two flexible layers surrounding the cell and enclosing its contents.  The membrane has a similar consistency Fluid-mosaic model? to olive oil.  The layers are embedded with protein and sugar molecules, communicating with the contents on either side of the cell membrane.  Everything inside the cell is known as intracellular fluid; everything outside the cell is extracellular fluid.  C.M allows cell-to-cell communication and also protects the organelles  3 layers: Lipids (phospholipids and cholesterol) proteins, and carbohydrate groups  THE CYTOPLASM Cell forming This is the region in the cell between the material nucleus and the plasma membrane. Most of the cellular activity occurs in the cytoplasm. The cytoplasm contents are contained by the cell membrane. The cytoplasm consists of: cytosol, a semi-transparent viscous liquid. It is made up of mainly water, but also proteins, sugars, sales and other solutes organelles suspended in the cytosol other chemical substances, depending on the function of the cell.  THE NUCLEUS Control centre The nucleus is the largest organelle. It contains DNA (deoxyribonucleic acid) which is our genetic material. Its function can be described as the board of directors, control centre, design departments and construction boss! Responsible for directing metabolic activities in the cells and for providing instructions for the synthesis of Nuclei = pit / kernel proteins in the cells. The majority of cells have one nucleus. However, some, including bone, skeletal, and liver cells, have many. Red blood cells are an exception, as their nuclei are ejected before the cells begin to circulate in the blood.  MITOCHONDRIA Power house These are organelles found in the cytoplasm. They are recognisable by their distinct sausage-shaped structures. They are involved in aerobic respiration - a process whereby energy is made available in the cell. It is often, as a result, referred to as the powerhouse of the cell. The more active a cell needs to be, the more mitochondria it has, eg muscle and liver cells.  CENTRIOLES These are small cylindrical organelles, found in pairs and positioned at right angles to each other. They’re usually located in close proximity to the nucleus. Each centriole is composed of short lengths of microtubules. They move to opposite ends of the cell (the poles) when it is time for cell division. They are involved in the development of spindles during cell division.  CELL COMMUNICATION OR CELL SIGNALLING There are four basic mechanisms for cellular communication: 1. Direct contact 2. Paracrine communication 3. Endocrine communication 4. Synaptic communication Direct contact communication – molecules on the 11 surface of one cell are recognized by receptors on the adjacent cell Gap Junction: 1. osteocyte of bone 2. Myofibres of Muscle cell Paracrine communication – signal released from a cell has 12 an effect on neighbouring cells. E.g Cell proliferation and growth Endocrine communication – hormones released from a cell affect other cells throughout the body 13 Synaptic communication – nerve cells release the signal (neurotransmitter) which binds to receptors on nearby cells. E.g 14 Between two neurons  SYNAPSE 15 AXON What is this The synapse - in the where the action membrane? happens Transport The next cell’s plasma protein membrane  That means that the impulse cannot be transmitted directly. Rather, the impulse is transmitted by the release of chemicals called chemical transmitters (or neurotransmitters).  INTRODUCTION TO CELL TRANSPORT What is Transport? Name of the life process in which materials are exchanged between an organism and its environment WHAT TYPES OF MATERIALS NEED TO BE TRANSPORTED INTO/OUT OF LIVING CELLS? INTO Cells OUT of Cells Water Carbon Glucose Dioxide Salt Waste Ions Materials Lipids Ions Amino Acids Water  SIMPLE AND COMPLEX Can be as simple as moving materials between one one-celled organism and its environment OR As complex as the transport systems in higher organisms Like Us! (Humans) IN ANY CASE BELOW, THE FINAL POINT OF TRANSFER IS: FLUID MOSAIC MODEL  FLUID MOSAIC MODEL Protein molecules are embedded in the phospholipid bilayer of most cell membranes. Because the protein molecules can move around and "float" among the lipids, and because so many different kinds of molecules make up the cell membrane, scientists describe the membrane as a fluid mosaic. WHAT ARE THESE DIFFERENT MOLECULES DOING? PROTEINS CARBOHYDRATES Form channels/pumps to help Many act like chemical move material across the identification cards, allowing cell membrane. individual cells to identify Attach directly to the one another. cytoskeleton, enabling cells to respond to their environment by using their membranes to help move/change shape Some materials are allowed to enter and leave the cell… some are NOT! SELECTIVELY PERMEABLE… All cells need to constantly exchange materials with its environment Many of these materials/substances can cross biological membranes freely. HOWEVER Some are too large or too strongly charged to pass across the cell membrane Also known as… Glucose, ions  CELL TRANSPORTATION The cell membrane has selective permeability. This means that only certain substances can come in and go out of the cell. Transportation across the cell membrane can occur in many different ways, depending on the size and characteristics of the substance. Two methods of transportation are diffusion and osmosis  DIFFUSION This is the movement of a chemical substance from an area of high concentration to an area of low concentration so that the solution is of equal concentration. It can occur in gases, liquids and solutions. Can you think of some examples? Coffee granules in a cup when water is added, squash in a glass when water is added, the smell of aroma from perfume or a diffuser. Source: magnetix/Shutterstock.com  DIFFUSION (CONT.) Diffusion can also occur across a semipermeable membrane. Only molecules able to cross the membrane will be able to diffuse through. Can you think of some examples where this occurs in the body? Through the plasma membrane, in the walls of alveoli in the lungs, capillary walls.  OSMOSIS This is the movement of water down its concentration gradient. This is often because the solute molecules are too large to pass through the pores of a membrane. The force with which this occurs is referred to as osmatic pressure - water is pulled from the dilute solution to the stronger solution across a membrane. Source: magnetix/Shutterstock.com E.g. 1. Dialysis of the kidney in the excretory system 2. Feeling thirty after taking salty food  CELL GROWTH AND REPRODUCTION The cell cycle is a series of changes from formation to the time it reproduces. There are two major periods within the cell cycle: Interphase: Cell growth and cellular routine activity. In addition to routine activities, the cell prepares for the next cell division.There are three sub-phases where the cell grows by producing proteins and organelles: 1. G1: the cell grows in size and volume. It may vary in length, but it’s usually the longest phase 2. S phase: the synthesis of DNA 46 chromosomes become 92. Chromatin is reproduced which is an essential component for the mitotic phase 3. G2: further growth and preparation Cell division/mitotic (M) phase  CELL DIVISION Cell division is essential for the growth and repair of tissues during normal use. When fully mature, some cells lose their ability to divide such as muscle and nervous cells, resulting in scar tissue. In most cells, the mitotic phase of the cell cycle involves two events: Mitosis (M phase): division of the cell Cytokinesis: division of the cytoplasm Another type of cell division, meiosis, occurs when the sex cells (ova and sperm) divide with only half the number of genes found in other cells. UNIT: CELL STRUCTURE AND FUNCTION LESSON: THE CELL CYCLE AGRISCIENCE INSTRUCTOR: STUDENT OBJECTIVES 1) Diagram and label the cell cycle and understand of each phase. 2) Identify cells in each stage of the cell cycle. 3) Understand how the cell controls cell division.  UNDERSTANDING THE CELL CYCLE There are three major stages to the cell cycle – Interphase, Mitosis and Cytokinesis. 1. Interphase encompasses the phases of G1 (Growth/GAP 1), S (DNA Synthesis) and G2 (Growth/GAP 2) phase. 2. Mitosis encompasses the phases of prophase, metaphase, anaphase and telophase. 3. Cytokinesis (cytoplasm divides) THE CELL CYCLE IN ACTION! WHY DO WE CARE ABOUT CELL DIVISION? A) Cell division is a process of reproducing cells. This occurs during growth, repair and development of tissues. WHAT IS THE CELL CYCLE? Repeating sequence of cellular growth and division throughout the life of an organism Interphase (GSG) Mitosis ( PMAT) Cytokinesis ( INTERPHASE – AN OVERVIEW 1st Growth Phase: gathering of material DNA Synthesis Phase: duplication of DNA 2nd Growth Phase: accumulation of nutrients. Check points  PHASES OF INTERPHASE A) 1st Growth Phase = (G1) 1. The cell grows rapidly and carries out routine functions 2. Phase takes most of the cell’s life 3. Muscle and nerve cells never divide, so they remain in G1 PHASES OF INTERPHASE (CONT.) B) Synthesis Phase (S) 1. Cell’s DNA is copied 2. At the end of the stage, each chromosome consists of 2 chromatids attached @ a centromere.  PHASES OF INTERPHASE (CONT.) C) Second Growth Phase (G2) 1. Hollow microtubules are assembled 2. Microtubules are used to move chromosomes during mitosis  SECOND PHASE OF THE CELL CYCLE D) Mitosis 1. Nucleus is divided into 2 nuclei 2. Each nucleus ends up with the same number of chromosomes as the original cell. 3. Includes :prophase, metaphase, anaphase and telophase. FINAL STAGE OF THE CELL CYCLE Cytokinesis 1. During this final stage, the cytoplasm divides. PLANT AND ANIMAL CELLS IN PROPHASE Plant & animal cells in prophase PLANT AND ANIMAL CELLS IN METAPHASE PLANT AND ANIMAL CELLS IN ANAPHASE PLANT AND ANIMAL CELLS IN TELOPHASE PLANT AND ANIMAL CELLS IN CYTOKENISIS  CONTROL OF CELL CYCLE There are three checkpoints: 1) G1 Checkpoint a. Decides when a cell can divide based on environmental conditions, health and cell size b. Favorable conditions begin S phase If not favourable, a resting period begins  CONTROL OF CELL CYCLE 2) G2 Checkpoint a) DNA repairs enzymes and checks DNA replication b) Once this checkpoint is passed, then mitosis begins 3)Mitosis Checkpoint a) Signals end of mitosis and G1 begins again  CONTROL OF CELL CYCLE What happens when checkpoints fail? 1. Cancer can occur Cancer is the uncontrolled growth of cells. 2. Mutation missed by checkpoint can cause overproduction of growth hormone 3. Damage done to a cell by environmental factors can cause cells to constantly repair