Human biology Cells: The Basic Units of Life Dr. Rawaa Salim Hameed
Reference Text book of human biology by John Kenneth Inglis 3 rd Ed (1985)
Cells: The Basic Units of Life
Cell theory Cell theory consists of three principles: All living things are made up of cells. Cells are the structural and functional unit of an organism. All cells come from pre-existing cells through cell division.
Types of cells All living cells can be divided into two groups: 1. Prokaryotic cells 2. Eukaryotic cells
Prokaryotic cells They have:- The hereditary material in the form of a single long strand of DNA No separate nucleus Fewer organelles in the cytoplasm A cell wall like plant e.g. bacteria.
Eukaryotic cells They have:- The hereditary material in the form of chromosomes A nucleus surrounded by a nuclear membrane Many organelles in the cytoplasm e.g. animals, plants and fungi.
Plants and animals Animal cells Plant cells 1- Cell wall is absent Cell wall is present 2- One or more small vacuoles One large central vacuole 3- Animal cells do not have chloroplast Plant cells have chloroplast
Cell shapes Cells come in different forms because they have different function:- Cube like cell, cubical cells which is seen in cuboidal epithelium Long column like the goblet cell Nerve cells have long projections that help them carry electrical messages to other cells Spindle shape in smooth muscle cells Rectangular shape in skeletal muscle which is multinucleated
What is the size of a cell? Some large cells e.g. an egg such as frogspawn can be seen with the unaided eye but most cells are much smaller and so we need a microscope to be able to examine them. Light microscopes can resolve structures that are 200 nm Electron microscopes can resolve structures that are 0.2 nm
Cells structures A cell consists of three main parts Nucleus Cell membrane Cytoplasm Within the cytoplasm are many parts that do different functions these parts are called organelles (small organs)
Typical animal cells
Nuclear membrane that has nuclear pores to permit the twoway traffic of large molecules Chromatin coils up into rod like chromosomes during cell division Nucleolus most nuclei contain at least one
Endoplasmic reticulum (ER) ER is a system of doublemembraned tubular canals found in the cytoplasm Rough endoplasmic reticulum contains ribosomes the site of protein synthesis Smooth endoplasmic reticulum without ribosomes
Golgi bodies (or Golgi apparatus) Its membranous sacs increased in size and filled up when a cell produced secretions. These packages of chemicals then snip off from the main Golgi bodies and migrate to the outer cell membrane where they discharge to the outside. The packages are called vacuoles or if they are extremely small, vesicles.
Lysosomes Lysosomes are vacuoles snip-off from Golgi apparatus. probably They contain enzymes (lysozymes) that break down the cell material itself by a process of self-digestion or autolysis.
The plasma membrane
The fluid mosaic model
Phospholipids
Mitochondria A fluid-filled tubular structure Surrounded by double membrane The inner membrane is folded into projections called cristae (energyproducing enzymes are located)
Cytoskeleton A network of protein fibres Help maintain the shape of the cell Secure some organelles in specific positions There are three types of fibres within the cytoskeleton: 1- Microfilaments 2- Intermediate filaments 3-Microtubules
Microfilaments The thinnest part of the cytoskeleton They made of the proteins actin and myosin Actin works with myosin to produce muscle movements and cell division.
Microtubules Microtubules are the largest element of the cytoskeleton. Small hollow tubes made of proteins called tubulin They are the structural elements of centrioles, cilia, and flagella
Centrioles They are extremely small tubules (microtubules) located in pairs near the nucleus. In the cross section, centrioles have a bundles of microtubules arranged in threes in a circle nine pairs (9+0 pattern).
Cilia and Flagella Cilia are short, hair-like projections from cell membranes They are lining the cells of the respiratory tract that trap particulate matter and prevents them getting into our lungs Flagella are similar to cilia but they are longer
Cilia and Flagella
Different types of cell junctions
Methods of Transport 1- Endocytosis: large molecules or other materials can enter the cell a. Cell eating is called Phagocytosis b. Cell drinking is called Pinocytosis
Exocytosis
3- Diffusion: Movement from high concentration to low concentration 4- Osmosis: The diffusion of water across a selectively permeable membrane from an area of high concentration of water to an area of low concentration
Solutions have an osmotic effect on our tissues that is dependent upon the strength of the solution compared with that of the body fluids:
Isotonic solutions: are those equal strength to our body fluids They therefore cause neither shrinking nor swelling of cells and tissue
Hypotonic solutions: contain less dissolved material and more water than the body fluids. This water passes into the cells by osmosis and causes them to swell up and eventually burst
Hypertonic solutions: contain more dissolved materials and less water than the body fluids. Water therefore leaves the cell by osmosis and causes them to shrink
5- Active transport: use energy to pump materials into the cell against the concentration gradient
6- Facilitated transport: this is a sort of faster diffusion It takes place along special protein pathways in the cell membrane across which chemicals can pass more quickly. These protein carriers take glucose and amino acids into cell quicker than would be expected for normal diffusion processes
Cell division In cell division, the cell that is dividing is called the "parent" cell. The parent cell divides into two or more "daughter" cells. The process then repeats in what is called the cell cycle Depending on the type of cell, there are two ways cells divide 1. Mitosis 2. Meiosis
Mitosis Division of somatic cells (non-reproductive cells) in eukaryotic organisms A single cell divides into two identical daughter cells Daughter cells have same number of chromosomes as does parent cell
Meiosis A single germ cell divides into four unique daughter cells. Daughter cells have half the number of chromosomes as parent cell, so they considered haploid.
The characteristics of living organisms Features Animals Plants Movement Very obvious Not very obvious Irritability (sensitivity) Obviously able to respond to such stimuli as light, Little obvious response to stimulation over a short temperature, changes, period of time Respiration vibration and touch Obvious organs associated with breathing No obvious breathing action nor any organ associated with respiration Nutrition Heterotrophic method Autotrophic method
Features Animals Plants Growth Cell number increase more rapidly in some areas of the body than the other. The skin for example is in a state of continuous repair or growth The increase number of cells is called growth. Cells divide by mitosis. Excretion There are obvious excretory organ (kidney, skin, lung) and obvious excretory products (urine, faces, water and carbon dioxide) There are no obvious organ of excretion or obvious excretory products except for water and carbon dioxide.
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