Lecture 2 - The Cell and its Components PDF

9/8/24 The Cell and its Components OpenStax Anatomy and Physiology textbook, chapter 3 1 Learning Objectives 1.) Describe the overall structure of the cell, as well as its main organelles. 2.) Underst...

9/8/24 The Cell and its Components OpenStax Anatomy and Physiology textbook, chapter 3 1 Learning Objectives 1.) Describe the overall structure of the cell, as well as its main organelles. 2.) Understand what stem cells are and how they differentiate into more specialized cells. 3.) Know the different types of stem cells. 2 The Cellular Level of Organization We are here! Image: OpenStax Anatomy and Physiology 2e 3 1  9/8/24 The Cell: Overview Each of us developed from a single fertilized egg cell into the complex organism that contains approximately 37.2 trillion cells. During this developmental process, early, undifferentiated cells differentiate and become specialized in their structure and function. Image: bdbiosciences.com 4 The Cell: Overview These different cell types form specialized tissues that cooperate to perform all the functions necessary for the living organism. Once specialized, cells in particular tissues show a distinct morphology (shape), behaviour (functions), and longevity. Image: bdbiosciences.com 5 The Cell: Overview For example, an epithelial cell will be relatively flattened (“squamous”) and live only for a short time before being shed and replaced. In contrast, a nerve cell has branch- like extensions and sends out a long process (axon) up to 1 m in length and may live for the entire lifetime of the organism. Images: bdbiosciences.com 6 2  9/8/24 The Cell Membrane Despite their differences in shape and function, all cells share a fundamental organization. The most basic of these is that all living cells have a surrounding cell membrane called a cell membrane. 7 The Cell Membrane The cell membrane provides a protective barrier around the cell and regulates which materials can pass in or out. The cell membrane is an extremely pliable structure composed primarily of back-to-back phospholipid molecules (termed a “phospholipid bilayer”). Image: OpenStax Anatomy and Physiology 2e 8 The Cell Membrane The cell membrane has many proteins, as well as other lipids (e.g. cholesterol), that are associated with the phospholipid bilayer. Some of the proteins are anchored into the phospholipid bilayer, others float freely in it. Water soluble vitamins easily pass through it. Image: OpenStax Anatomy and Physiology 2e 9 3  9/8/24 The Cell Membrane Membrane proteins are categorized as either integral or peripheral. Integral proteins have both hydro-phobic and hydrophilic regions (i.e. amphipathic). This dual nature allows integral proteins to embed fully or partially into cell membranes. An example is a channel protein. Image: OpenStax Anatomy and Physiology 2e 10 The Cell Membrane Some integral membrane proteins are glycoproteins. A glycoprotein is a protein that has carbohydrate molecules attached, which extend into the extracellular matrix. The attached carbohydrate tags on glycoproteins function in cell-cell recognition. Red blood cells have 50+ such proteins. Image: OpenStax Anatomy and Physiology 2e 11 The Cell Membrane Some integral membrane proteins are glycoproteins. A glycoprotein is a protein that has carbohydrate molecules attached, which extend into the extracellular matrix. The attached carbohydrate tags on glycoproteins function in cell-cell recognition. Red blood cells have 50+ such proteins. Image: OpenStax Anatomy and Physiology 2e 12 4  9/8/24 The Cytoplasm and Cellular Organelles Image: OpenStax Anatomy and Physiology 2e 13 The Cytoplasm Image: OpenStax Anatomy and Physiology 2e 14 The Cytoplasm The cell membrane of all living cells encapsulates the cytoplasm. Cytoplasm consists of cytosol, a jellylike substance within the cell, and the organelles of the cell. Organelle means “little organ”. They are essentially the organs of your cells. Enzymes, other molecules, and solutes (such as ions) are dissolved within the cytoplasm. 15 5  9/8/24 The Nucleus Image: OpenStax Anatomy and Physiology 2e 16 The Nucleus All human cells (except mature red blood cells) exhibit a DNA- enclosing structure called a nucleus. The nucleus has a double membrane (the nuclear envelope) with a thin, fluid-filled space in between. The nuclear envelope is perforated by nuclear pores. Image: OpenStax Anatomy and Physiology 2e 17 The Nucleus Some cells in the body can be multinucleated. Image: OpenStax Anatomy and Physiology 2e 18 6  9/8/24 The Nucleus Whereas other cells eject their nucleus. Image: OpenStax Anatomy and Physiology 2e 19 The Nucleus Within the nucleus are DNA molecules (chromosomes), associated proteins, and one or more spherical organelles called nucleoli. The chromosomes are normally present as partly wound up and partly loose strands of DNA. In this state they are called chromatin. Image: OpenStax Anatomy and Physiology 2e 20 The Nucleus Image: OpenStax Anatomy and Physiology 2e 21 7  9/8/24 The Nucleus The nuclear envelope is perforated by numerous protein-bound channels called nuclear pores. RNA and other molecules move from the nucleus to the cytoplasm via these pores. The nucleoli synthesize tiny organelles called ribosomes, which are transported to the cytoplasm. Image: OpenStax Anatomy and Physiology 2e 22 Ribosomes Image: OpenStax Anatomy and Physiology 2e 23 Ribosomes Ribosomes are made of protein and rRNA (ribosomal ribonucleic acid). They are protein-synthesizing organelles. They link the building blocks (amino acids) of proteins (polypeptides) based on the code recorded in messenger RNA via a process called gene expression. Ribosome Image: OpenStax Anatomy and Physiology 2e 24 8  9/8/24 The Endoplasmic Reticulum Image: OpenStax Anatomy and Physiology 2e 25 The Endoplasmic Reticulum The nuclear envelope is continuous with a neighbouring organelle called the endoplasmic reticulum (ER). There are two types of ER. Rough ER functions in the synthesis and modification of proteins destined for the plasma membrane or export from the cell. Image: OpenStax Anatomy and Physiology 2e 26 The Endoplasmic Reticulum The membranes of rough ER are arranged somewhat like stacks of pancakes or pita bread. 100s to 1000s of embedded ribosomes give it a grainy appearance in SEMs. Image: OpenStax Anatomy and Physiology 2e 27 9  9/8/24 The Endoplasmic Reticulum Smooth ER is net-like in structure and lacks ribosomes. It synthesizes lipids, such as phospholipids. Image: OpenStax Anatomy and Physiology 2e 28 The Golgi Apparatus Image: OpenStax Anatomy and Physiology 2e 29 The Golgi Apparatus The Golgi apparatus functions in sorting, modifying, and shipping off products that come from the rough ER. Products (e.g. digestive enzymes) are sorted through a Golgi apparatus, and then they are released from the opposite side after being repackaged into vesicles. Image: OpenStax Anatomy and Physiology 2e 30 10  9/8/24 The Mitochondria Image: OpenStax Anatomy and Physiology 2e 31 The Mitochondria The mitochondria (singular = mitochond-rion) are membranous, bean-shaped organelles that are the “power station” of the cell. Producing ATP (adenosine triphosphate). Mitochondria consist of an outer lipid bilayer membrane as well as an inner lipid bilayer membrane. They have their own DNA. Image: OpenStax Anatomy and Physiology 2e 32 The Mitochondria Mitochondria produce over 90% of a cell’s energy needs, but they need oxygen for the process of oxidative metabolism. Highly active cells that require lots of energy each may contain 1000s of mitochondria. Muscle cells are packed full of mitochondria because they use huge amounts of ATP. Image: OpenStax Anatomy and Physiology 2e 33 11  9/8/24 The Mitochondria Nerve cells are also highly active and contain several hundred to 1000s of mitochondria. On the other hand, a mature bone cell (osteocyte), which is not nearly as metabolically active, might only have a couple hundred mitochondria. 34 Cellular Differentiation This is the process by which a complex organism such as a human develops from a single cell—a fertilized egg—into the vast array of cell types such as nerve cells, muscle cells, epithelial cells, etc., that characterize the adult. Image: bdbiosciences.com 35 Cellular Differentiation Throughout development and adulthood, the process of cellular differentiation leads cells to assume their final morphology and physiology. Differentiation is the process by which unspecialized cells become specialized to carry out distinct functions. Image: bdbiosciences.com 36 12  9/8/24 Stem Cells A stem cell is an unspecialized cell that can divide without limit. It can, under specific conditions, differentiate into specialized cells. Stem cells are divided into several categories according to their potential to differentiate: totipotent, pluripotent, or multipotent. Image: bdbiosciences.com 37 Stem Cells The first embryonic cells that arise from the division of the zygote are the ultimate stem cells. These stems cells are described as totipotent (Latin totus: whole) because they have the potential to differentiate into any of the cells needed to enable an organism to grow and develop. Image: OpenStax Anatomy and Physiology 2e 38 Stem Cells The immediate descendants of totipotent stem cells, and the precursors to the fundamental tissue layers of the embryo, are classified as pluripotent. A pluripotent stem cell has the potential to differentiate into any type of human tissue but cannot support the full development of an organism. Image: OpenStax Anatomy and Physiology 2e 39 13  9/8/24 Stem Cells As pluripotent cells become slightly more specialized, they are referred to as multipotent cells. A multipotent stem cell has the potential to differentiate into different types of cells within a given cell lineage (or small number of lineages), such as a red blood cell or white blood cell. Image: OpenStax Anatomy and Physiology 2e 40 Stem Cells Image: OpenStax Anatomy and Physiology 2e 41 Stem Cells Stem cells are unique in that they can continually divide and regenerate new stem cells instead of specializing. There are different stem cells present at different stages of a human life span. They include embryonic stem cells of the embryo and adult stem cells in the adult. Image: OpenStax Anatomy and Physiology 2e 42 14  9/8/24 Stem Cells One type of adult stem cell is the epithelial stem cell, which gives rise to the keratinocytes that form the strata of epithelial cells in the epidermis of skin. Adult bone marrow has three types of stem cells: hematopoietic, endothelial, and mesenchymal stem cells. 43 Stem Cells Hematopoietic stem cells give rise to red blood cells, white blood cells, and platelets. Endothelial stem cells give rise to the endothelial cell types that line blood vessels and lymph vessels. Mesenchymal stem cells give rise to the different types of muscle cells. 44 Stem Cells Image: OpenStax Anatomy and Physiology 2e 45 15  9/8/24 The Cell: Summary 1.) Describe the overall structure of the cell, as well as its main organelles. 2.) Understand what stem cells are and how they differentiate into more specialized cells. 3.) Know the different types of stem cells. 46 Readings for next lecture: Tissue Types and Injury -OpenStax Human Anatomy and Physiology textbook, chapter 4 47 16