ABN1 Intro to Cells PDF Notes

Introduction to cells N1239: Applied Bioscience for Nursing Practice 1 Natasha Price, September 2024 1  Cells → Tissues → Organs → Bodies...

Introduction to cells N1239: Applied Bioscience for Nursing Practice 1 Natasha Price, September 2024 1  Cells → Tissues → Organs → Bodies Organs are organised into systems 2 or more tissue types aggregate to form organs Cells of similar structure & function are organised into tissues Systems link together to form individual entities 2  Two main classes of cells Prokaryotic cells Organelles not bound by membranes Bacteria Eukaryotic cells (eg human, animal, plant, fungi) Nucleus bound by membrane Possess many organelles Prokaryotes: Nucleus and single, circular chromosome; example is bacteria Eukaryote; Complex cellular organization; contains many organelles such as a nucleus; Membrane-bound organelles; Well-defined nucleus; Higher animals, plants, fungi, and protozoa. We will explore more about prokaryotic cells when we look at the human microbiome later. 3  The animal (human) cell Cells are building blocks of the body and there are many types each with its own size, shape and function (for example, skeletal muscle cells may be up to 30cm along the muscle while red blood cells are small biconcave discs about 8um long). Cells are the smallest functional unit of the body and grouped to form tissues with specialised function- muscle, bone, skin etc. Tissues are grouped to form organs as part of body systems. Homeostasis is about how these work together to maintain a healthy balanced state. All body functions depend on the integrity of the cells. Cellular biology - how cells behave, reproduce and communicate is key to understanding disease. Cells are replaced through processes of cell division, and as cells reach the end of their lifespan they are programmed to ‘self-destruct’ and components are removed by phagocytosis (this process is called apoptosis) 4  Plasma (cell) membrane Influences the movement of substances in and out of the cell Regulates cellular response to signals from hormones and neurotransmitters Is composed of a bilipid layer of phospholipids, containing proteins and sugars. Cell or plasma membrane influences the movement in and out of the cell. It is essential it is intact. It also regulates cellular responses from hormones and neurotransmitters. Bi-lipid layer; proteins, sugars and cholesterol. Proteins in the membrane extend all the way through to provide channels to allow passage of electrolytes, non-lipid substances. Proteins such as peptides are receptor (specific recognition sites) for hormones and other chemical messengers. 5  The plasma membrane separates intracellular components and interstitial fluid outside the cell. Phospholipid layer. The lipids are arranged so their fatty acid chains (hydrophobic or water hating) are pointing inwards and their hydrophilic (water loving) polar heads pointing out to the aqueous phase. It is very stable, and proteins are either across the lipid layer or anchored it in in various ways. The structure is important in influencing how substances transfer across the membrane. Membrane proteins attach to carbohydrate molecules to give the cell immunological identity; the protein molecules also act as receptors for specific hormones and chemical messengers; some proteins are enzymes, and some transmembrane proteins form channels that are filled with water and allow small water-soluble ions to cross; and some are involved in pumps to transport substances across the membrane, for example the sodium/potassium pump. 6  Cytoplasm Fills the space between the nucleus and the plasma membrane Contains the organelles and other substances* Gelatinous, semiliquid (cytosol) 55% of the total cell volume Functions: Synthesis and transport Eliminates wastes Metabolic processes Maintenance Motility Storage Cytosol is the liquid found inside of cells. It is the water-based solution in which organelles, proteins, and other cell structures float. The cytosol of any cell is a complex solution, whose properties allow the functions of life to take place. *Cytosol contains substances including proteins, amino acids, mRNA, ribosomes, sugars, ions, and messenger molecules. 7  Nucleus Largest organelle Contains genetic material and directs metabolic activities Nuclear membrane/envelope of lipid layers Contains Deoxyribonucleic acid (DNA) When not dividing, DNA is present in threads (chromatin) When preparing to divide, forms into chromosomes Ribonucleic acid (RNA) also found in nucleus and has role in manufacturing new proteins. The nucleus is the largest organelle and is contained in a nuclear membrane or envelope which has 2 lipid layers with tiny nuclear pores that provide a means of communication. All cells have a nucleus apart from the mature erythrocyte. Skeletal muscle cells contain several nuclei (multinucleated). Contains the DNA which directs all the metabolic activities. When not dividing, the DNA is present in a network of chromatin; when it prepares to divide it forms into forms chromosomes. RNA is also in the nucleus- there are different types but mostly involved in protein synthesis. The nucleolus is prominent in the nucleus and manufactures the ribosomes- they are important in the synthesis of new proteins molecules. 8  Deoxyribonucleic acid (DNA) DNA acts as the genetic code which provides instructions for the formation of RNA (Ribonucleic Acid), RNA is transported out of the nucleus and provides a code for the formation of proteins (in collaboration with ribosomes). The proteins synthesised from RNA may form: Structural proteins, part of the structure of the cell or the matrix surrounding it. Functional proteins, which are the body’s “biochemical machinery”. DNA in the chromosomes carries the genetic material that determines the individual’s characteristics. It does this by acting as a template for the formation of the proteins of the body from the amino acids, the nutrients absorbed into the body after the breakdown of proteins in the diet. This determines both structure and function of the components of the body. Functional proteins include things like enzymes and hormones. Haemoglobin is a functional protein molecule which helps to transport oxygen in the blood. We will learn more about protein molecules later. 9  Protein synthesis is via processes called protein transcription and protein translation. Please watch this short video which explains protein synthesis https://youtu.be/oefAI2x2CQM The Amoeba Sisters on YouTube is an excellent resource! 10  Mitochondria: “Powerhouse of the cell” Structure Surrounded by a double membrane. Increased inner membrane surface area is provided by cristae (ATP synthesis). Functions Aerobic respiration and production of energy in the form of Adenosine Triphosphate (ATP) Sausage shaped, central to aerobic respiration, the process through which chemical energy is made available in the cell. They metabolise nutrients to produce ATP (Adenosine Triphosphate) – the energy store of the cell – which is used to power the cell’s activities. Mitochondria are surrounded by a bilipid layer similar to the plasma membrane. They have an outer and inner membrane, and the inner is thrown into folds (cristae) where synthesis of ATP takes place. Cells which have a high energy requirement will have more mitochondria, for example skeletal muscle cells. 11  Other cytoplasmic organelles Endoplasmic reticulum Network of tubular or saclike channels; smooth and rough endoplasmic reticulum Site of protein synthesis (enzymes and hormones) Rough ER is studded with ribosomes Ribosomes Tiny granules of Ribonucleic acid (RNA) and protein Synthesize proteins such as enzymes for metabolism Endoplasmic reticulum- series of interconnecting membranous canals in the cytoplasm- rough and smooth types. Smooth synthesizes lipids and steroid hormones and detoxifies some drugs and may be used to repair the plasma membrane. Rough is studded with ribosomes- they are the site of proteins synthesis- enzymes and hormones and leave the cell by exocytosis to be used by other cells. Ribosomes are tiny granules of proteins and ribonucleic acid RNA, formed on nucleolus and migrate to cytoplasm, occur in groups of polyribosomes and help synthesise new proteins (amino acids). Ribosomes are also found on the outer surface of the nuclear envelope and rough ER where they make proteins to be exported from the cell. Some attach to ER, which is the site of protein synthesis. Rough ER is studded with ribosomes. 12  Golgi complex/body/apparatus Structure Stacks of closely folded, flattened, smooth membranes Proteins move from the endoplasmic reticulum and are stored in the Golgi complex Functions Processes, secretes, and releases substances, especially protein from cells “Refining plant” GC is system of membranous sacs that modify and package proteins for secretion. The proteins can move to plasma membrane to be expelled from the cell when required (exocytosis). In secreting cells (such as the acinar cells of the pancreas or mucus secreting cells such as the Goblet cells), the GC is between the nucleus and the apical surface where secretion take place. The GC is really an extension of the endoplasmic reticulum- small vesicles called transport vesicles move from the ER to the GC and fuse with it. 13 This is a nice image to help reorientate to the cell’s “geography”. It also shows the transport from the ER to the Golgi body, and the transport and secretory vesicles. Some of the proteins are exported and others stay for use within the cell. (Don’t worry about the names of the regions of the Golgi body) 14  Lysosomes Sac-like structures that originate from the Golgi body. Contain enzymes to break down wastes inside the cell. The breakdown products can be recycled within the cell, or removed. A type of intracellular digestive system- contain enzymes that allow cells to digest materials (RNA, DNA and proteins) inside the cell. In white blood cells the lysosomes contain enzymes that digest microbes as part of phagocytosis. 15  Cytoskeleton The cytoskeleton provides structure and shape to the cell and is comprised of microfilaments, microtubules and intermediate filaments. It is responsible for the movement and the cell itself and its organelles. Microfilaments (actin filaments) are small dynamic protein fibres that maintain the cell shape and permit contraction, occur in a cell in the form of meshworks or bundles of parallel fibres. This allows the cell to “remodel” in shape. The constantly changing arrays of actin filaments help move the cell and mediate specific activities within it, such as cell cleavage during mitosis. Microtubules are longer filaments that are constantly assembling and disassembling. They have several functions. They provide the rigid, organized components of the cytoskeleton that give shape to cells, and they are major components of cilia and flagella (cellular locomotory projections). They participate in the formation of the spindle during cell division (mitosis). They also assist the movement of organelles (e.g., mitochondria), as well as the movement of vesicles from the cell bodies of neurons to the axonal tips and back to the cell bodies. Intermediate filaments are very stable structures that form the true skeleton of the cell. They anchor the nucleus and position it within the cell, and they give 16 the cell its elastic properties and its ability to withstand tension. 16  The cell cycle Cells go through a series of events in a specific order to divide (mitosis). The parent cell grows in size, makes a copy of its genetic material, then splits to produce two daughter cells. Damaged, dead or worn-out cells can often be replaced by cell division to maintain tissue integrity/function. The cell cycle is the period between two cell divisions. It varies by cell type. The cell cycle and frequency of cell division is carefully regulated for effective maintenance of body tissues. 17  Cell division Please watch the video: https://youtu.be/f-ldPgEfAHI?si=JMCEVu1obXQDbLbY Video link: https://youtu.be/f-ldPgEfAHI?si=JMCEVu1obXQDbLbY 18  Apoptosis is a normal, genetically programmed destruction of a cell at the end of its life cycle. It shrinks and breaks apart, and components are removed by a process called phagocytosis. As we age, fewer cells lost by apoptosis are replaced, leading to declining tissue and organ mass. The cell cycle and frequency of cell division is carefully regulated for effective maintenance of body tissues. 19  Apoptosis vs Necrosis Cell death by necrosis is different to apoptosis. Necrosis is cell death due to lack of oxygen (hypoxia). The plasma membrane ruptures. Cellular contents are released triggering an inflammatory response. Inflammation is the first stage of tissue repair and is needed to clear cell debris. We will learn about the inflammatory response in the haematology unit which includes white blood cells and immunity. 20  Further reading: Ross and Wilson’s anatomy and physiology in health and illness, chapter 3. 21