A&P 1, Chapter 3, Anatomy of the Cell

Define the term "chromatin" and explain the relationship between chromatin and chromosomes.

"Material composed of DNA and proteins and makes up chromosomes" - During cell division chromatin condenses into super coiled X-shaped structures called chromosomes - In nucleoplasm of the nucleus, made up of DNA and globular proteins called histones - Single DNA strand winds around 8 histone molecules, forming a nucleosome - Histones keep DNA strand untangled and organized, and expose small sections (genes) to the outside. Called Gene Regulation

Explain the importance of cilia and flagella.

- Cilia - Move fluid, mucus, and debris across cellular surface - Upper respiratory tract, moves bacteria and mucus away from lungs - Oviduct, pulls egg away from the ovary into the opening of the oviduct - Flagella occurs singly, longer than Cilia, attached to single cells, propel cell forward by undulating - Sperm - Flagella move cell through fluid, Cilia moves fluid across cell surfaces - Both are extensions of the cell membrane

Describe the structure and functions of each of the cellular organelles, inclusions, and vesicles. Then draw a diagram of each. Why do inclusions vary in appearance?

1. Mitochondria - Double membrane bound organelles, internal membrane folds inward foming cristae and giving increased internal surface area - Site of cellular respiration, which produces ATP 2. Endoplasmic reticulum - A system of collapsed sex extending from the outer layer of the nuclear in has 2 forms: RER with ribosomes and SER without ribosomes - RER produces, modifies and packages secretory proteins. SER produces, modifies and packages lipids and carbohydrates 3. Ribosome - One large, one small, fit like cupped hands. Each made of RNA and protein. Fixed on RER, free float in cytosol - Sight of protein synthesis. Protein manufactured on fixed ribosomes is intended for export; protein manufactured on free ribosomes is intended for intracellular use. Ribosomal subunits are manufactured in nucleoli. 4. Proteasome - Hollow cylinder composed of protein subunits and On each end. About half the size of a ribosome - Responsible for breaking down individual mis folded or abnormal protein molecules. Like ribosomes, is found throughout the cytosol 5. Golgi apparatus - Network of connected flatten tubes stacked on top of one another - Refines and alters molecules intended for both secretion and internal use. Produces lysosomes 6. Lysosomes - Vesicle filled with hydrolytic enzymes; formed by Golgi apparatus - Digestion of absorbed material and internally produced waste. Rupture causes cellular autolysis 7. Peroxisomes - Membrane-bound vesicle containing enzymes: produced by fission - Detoxify various molecules such as alcohol and formaldehyde; remove free radicals 8. Vaults - Tiny barrel-shaped capsule composed of RNA (vRNA) and protein. Thought to be very numerous in cells - Perhaps able to fit in the nuclear pore complexes where one end opens to pick up or drop off molecules entering or exiting the nucleus 9. Inclusions - Vesicles, vacuoles, and lipid droplets suspended in cytosol - No storage and transportation vesicles of intracellular substances 10. Cytoskeleton - Structural complex within cytosol composed of microtubules, intermediary filaments, and microfilaments - Provides strength, structure, and support. Maintains cell shape, and affects cell division and movement of organelles and the cell membrane 11. Centrioles - Found in the center of the centrosome near the nucleus. Composed of microtubules arranged in a pinwheel. Asters radiate away from the centrioles - Duplicate prior to cell division. Mother and daughter centrioles. Help anchor spindle fibers. 2 pairs of centrioles move apart as spindle fibers lengthen

Can a cell with no nucleus live as long as a cell with one, why or why not?

All cells have different life spans: some are very short lived, while other cells live a long time. However, a cell that lacks a nucleus does not have the instructions (DNA) to make protein and therefore it cannot repair itself and will die sooner than if it had the ability to repair and maintain itself.

Draw a picture of each of the 8 organelles described earlier

As you make your drawings, be sure to include the following organelles: mitochondria, ribosomes, rough and smooth endoplasmic reticulum, Golgi apparatus, lysosomes, proteasomes, peroxisomes, and vaults.

What role does the centriole play in the formation of cilia and flagella?

Centrioles form the bases of cilia and flagella and in this role are known as basal bodies.

Which are found more commonly in mammalian cells: cilia or flagella?s

Cilia

What is cytosol and what kind of molecules are found in it?

Cytosol is the protoplasm of the cell. It is a viscous, semitransparent liquid composed of dissolved electrolytes, amino acids, and simple sugars. Proteins are also suspended in the cytosol and give it its thick, jellylike consistency.

3-3 What are the principal components of cytoplasm?

Cytosol, cytoskeleton, organelles, and inclusions

What is the difference between a prokaryote and a eukaryote?

Prokaryotes do not contain nuclei. Eukaryotic cells have a distinct nucleus in which the DNA has combined with protein to form chromosomes. These, in turn, are surrounded by a protective nuclear envelope.

Differentiate between prokaryotic and eukaryotic cells.

Prokaryotic - no nucleus Eukaryotic - nucleus

Draw a picture of the lipid bilayer, which part is hydrophobic and hydrophilic?

The hydrophilic heads of the phospholipid bilayer are attracted to the aqueous environments found in the extracellular and intracellular spaces. The lipid tails, on the other hand, are hydrophobic and are repelled by these aqueous compartments. Therefore, they are turned inward and face one another inside the bilayer.

How many types of fiber make up the cytoskeleton? Can you name them? How do they function differently?

Three different types of fibers compose the cytoskeleton, all of which are made of protein. The fibers are microtubules, intermediate fibers, and microfilaments. Microtubules form secure "cables" to which mitochondria, lysosomes, and secretory granules attach. Proteins that act as "motors" move the attached organelles along the microtubule from one location in the cell to another. Because microtubules act as the "railroad tracks" for organelle travel, they can be easily disassembled and then reassembled to form new paths or take a new direction. Intermediate fibers are woven, ropelike fibers that possess high tensile strength and are able to resist pulling forces on the cell by acting as internal guide wires. These fibers are the toughest and most permanent element of the cytoskeleton. Microfilaments play a key role in the cell's ability to change shape, break apart during cell division, and form outpouchings and involutions. In most cells, microfilaments are assembled where and when needed.

Explain how scientists believe the earliest cells may have formed on earth.

- 3 billion years ago - lightning and sun radiation caused methane (CH⁴), water and ammonia (NH³) to collide and split apart - organic molecules were formed and washed into the ocean by rain - proteins, lipids, and carbohydrates evolved and over time arranged themselves into cells

Describe the structure and functions of the cytoskeleton.

- Flexible 3-dimensional frame for the cell - Changes with activities of the cell gives support and shape to cell, enables it to move, provides direction for metabolic activity, anchors organelles 3 types - Microtubules: thickest fibers, long hollow tubes radiate out from center of cell. Organelles can attach and be transported by motor proteins. Easily disassembled and reassembled to make new paths - Intermediate fibers: toughest and most pemanent, woven like a rope, high tensile strength, and can resist forces pulling on cell - Microfilaments: near cell surface, arranged in bundles and mesh works, composed of Actin and Myosin, help change cells shape, break apart during division, and form outpouchings and involutions - made when and where needed

Describe the consistency and molecular components of cytosol.

- Fluid of cell - Viscous, semi transparent liquid - Composed of dissolved electrolytes, amino acids, and simple sugars - Proteins suspended inside cytosol give it a thick, jelly like consistency (mostly enzymes important in metabolic activities of the cell)

List the physiologic factors that limit cell size.

- Volume to surface area: Restricted to a range of 10 to 30 um in diameter because of the relationship between surface area and internal volume of a cell - Nutritional requirements - a small cell has a small internal area relative to its surface area. A large surface area allows for greater absorption of nutrients - Limitations in governing capability - a single nucleus can control the metabolic activity of a small cell better than a large one

List the early discoveries of the 17th, 18th, and 19th centuries that led to our modern understanding of cells.

17th century, 1600s - Robert Hooke observed tiny units that make up cork - Anton van Leeiwenhoek found microscopic creatures in pond water (first living cells) 18th century - not much happened 19th century - Francoise Raspail established one of the concepts of cell theory: that all cells arise from pre-existing cells. The basis of this was the witnessing of binary fission under a microscope wherein a single cell divided into two daughter cells. - Theodore Schwann and Matthias Scleiden proposed the cell theory in 1836. The concept of the theory holds that: (1) The cell is the unit of structure, physiology, and organization in living things, (2) The cell retains a dual existence as a distinct entity and a building block in the construction of organisms, (3) Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation). - The third doctrine of Schwann and Scleiden was proven wrong by Rudolf Virchow. Said "All cells only arise from pre-existing cells"

How do histones play a role in gene regulation?

A single strand of DNA winds around eight histone molecules, forming a granule called a nucleosome. The nucleosomes are held together by short strands of DNA called linker DNA. Not only do the histone proteins help keep the DNA strand organized and untangled, but they also expose small sections of the DNA (genes) to the outside nucleoplasm. By changing shape, the histones can expose different sections of DNA, called genes, at different times. A gene is the length of DNA needed to make one peptide (a short chain of amino acids). The exposed genes determine what proteins will be made by the cell. In this way, histones play an important role in regulating gene expression (gene regulation). DNA contains the instructions required for synthesis of thousands of different proteins, but not all of them are made. Only a small percentage of the possible thousands of proteins are actually manufactured. Histones help determine which segments of DNA will be expressed and therefore which proteins will be made.

Compare and contrast the molecular structure of DNA and RNA.

Both made up of nucleotides (nitrogenous base, 5 carbon sugar, phosphate group). Alternate sugar and phosphate in a backbone, the nitrogenous base sticks out. DNA = double strand, deoxyribose sugar; adenine, cytosine, guanine, thymine RNA = single strand, ribose sugar; adenine, cytosine, guanine, uracil

What are CAMs & what do they do?

CAM refers to cell adhesion molecules, which are sticky glycoproteins (part of the glycocalyx) that cover the surfaces of almost all cells in mammals and allow them to bond to extracellular molecules and to each other. These molecules are also important in helping cells move past one another and in signaling circulating cells, such as white blood cells, to areas of inflammation or infection.

What are caveolae and what role do they play in the cell membrane?

Caveolae are minute invaginations of the cell membrane, like tiny dimples. Caveolae often pinch off entirely from the cell membrane, forming vesicles. These vesicles can form singly or in clusters (like tiny rosettes). Caveolae are formed only from rafts in the cell membrane that contain the protein caveolin.

3-1 What are the basic cellular functions that define life?

Cells can grow, develop, reproduce, adapt, become influenced by outside stimuli, maintain a stable internal environment, and convert food into usable energy. Each cell carries vital genetic material that governs its own development, metabolism, and specialization.

How are centrioles structurally similar to cilia and flagella?

Centrioles are structurally similar to cilia and flagella because all consist of microtubules. Centrioles are small, hollow cylinders composed of microtubules. Cilia and flagella are composed of nine pairs of microtubules that encircle a central pair of microtubules.

How are cilia and flagella different?

Cilia occur in large numbers on the exposed surface of some cells. They are shorter than flagella and measure only about 10 mm long. They move synchronously, one after the other, creating waves of motion that propel fluid, mucus, and debris across the cell surface. Cilia are best known for their important functions (1) in the upper respiratory tract, where they propel bacteria and mucus away from the lungs, and (2) in the oviduct, where their beating motion pulls the ovulated egg away from the ovary and into the opening of the oviduct. Flagella generally occur singly and are significantly longer than cilia. They are typically attached to individual cells and propel the cell forward by undulating. Flagella move cells through fluid, whereas cilia move fluid across cell surfaces. The tail of a sperm cell is an example of a flagellum.

List and describe the components of cytoplasm.

Cytosol: The cytosol is the semi-fluid component or liquid medium of a cell's cytoplasm. It is located outside of the nucleus and within the cell membrane. Organelles: Organelles are tiny cellular structures that perform specific functions within a cell. Examples of organelles include mitochondria, ribosomes, nucleus, lysosomes, chloroplasts, endoplasmic reticulum, and Golgi apparatus. Also located within the cytoplasm is the cytoskeleton, a network of fibers that help the cell maintain its shape and provide support for organelles. Cytoplasmic Inclusions: Cytoplasmic inclusions are particles that are temporarily suspended in the cytoplasm. Inclusions consist of macromolecules and granules. Three types of inclusions found in the cytoplasm are secretory inclusions, nutritive inclusions, and pigment granules. Examples of secretory inclusions are proteins, enzymes, and acids. Glycogen (glucose storage molecule) and lipids are examples of nutritive inclusions. Melanin found in skin cells is an example of a pigment granule inclusion.

What are these proteins' location and functions? Add them to your drawing

Integral and peripheral proteins are types of globular proteins. Some integral proteins are located within the bilayer, spanning it. These form selective passageways and pores that permit only particular substances to enter or exit the cell. Some integral proteins are membrane receptors that act as binding sites on the cell's surface. Peripheral proteins are bound to the inside and outside surfaces of the cell membrane and sometimes act as enzymes to catalyze specific chemical reactions. They may also be involved in the mechanics of changing the cell's shape. Glycoproteins, in addition to glycolipids, are the principal components of the "sugar coating" that covers the surface of some cells. This coating is called the glycocalyx.

What are the membrane receptors & ligands and what role do they play in the health of cells? How does obesity affect cell membrane receptors for insulin?

Membrane receptors are integral proteins and glycoproteins that act as binding sites on the cell surface. Some of them play a vital role in cell-to-cell recognition, a process called contact signaling. This is particularly important during cell-mediated immune responses and helps bacteria and viruses find preferred "target" cells. Membrane receptors are also involved in a process called chemical signaling. Hormones, neurotransmitters, and other chemical messengers called ligands bind to specific binding sites on cell surfaces. Once bound to the cell membrane, ligands can bring about a change in the cell's activity. Some ligands act as enzymes to activate or inactivate a particular cellular activity.

List the parts that make up the nucleus; for each part, explain its structure and function.

Nucleus - wide variety of shapes, sizes and numbers. Contains nucleoplasm, DNA, rRNA, and ribosomal subunits. - Site of transcription and production of ribosomal subunits Nuclear envelope - double layered membrane with nuclear pore complexes. Outer membrane continuous with ER - Separates nucleus from cytosol; restricts movements of molecules in and out Chromatin - located in nucleoplasm. Composed of nucleosomes (DNA and 8 histones) connected by linker DNA. Arranged in loose strands - DNA portion contains sequence codes for proteins, and enzymes that control molecular interactions. Supercoils to form X-shaped chromosomes during cell division Nucleolus - dense cluster of ribosomal RNA and protein, not membrane bound - Location of synthesis of ribosomal subunits

Describe the molecular structure of the cell membrane.

Phospholipid bilayer - Hydrophilic heads on outside, hydrophobic lipid tales on the inside Thin - 60 to 100 angstroms Proteins suspended in bilayer move easily throughout membrane, creating a changing pattern, creating fluid mosaic Lipid soluble passes through easily, ionized and water soluble don't - amino acids, sugars, proteins Cholesterol between phospholipids stabilizes it, keeps it fluid, adds to the oily nature of the internal layer Integral proteins - span membrane, some are channel proteins Glycocalyx - covers outside, important in cell recognition, contact signaling and cell mediated immunity - includes cell adhesion molecules (CAM) and receptors Rafts - organized functional areas on cell surface - rigid area of phospholipids, cholesterol, and protein

What are the molecular components of rafts & what role do they play in the life of a cell?

Rafts are composed of densely packed phospholipids, cholesterol, and protein. These dense regions are stiff and form rigid, raftlike structures within the otherwise fluid phospholipid bilayer of the cell membrane.

Why are cells not the size of watermelons?

Smaller cells have smaller nutritional requirements than large cells but have a proportionately larger surface through which they can absorb the substances they need. Thus smaller cells are able to complete their metabolic functions more rapidly and efficiently than large cells. If cells were the size of watermelons, they would not be able to take in nutrients fast enough to feed themselves and would die. A second limiting factor in cell size is related to the governing capability of the nucleus. A single nucleus can control the metabolic activity of a small cell better than it could a large one. Also, the more active a cell is, the greater its metabolic needs. Therefore, it is not surprising that very large cells or cells that are more active, such as cardiac and skeletal muscle cells, have two or more nuclei.

3-4 Why do inclusions vary in appearance? What function do they perform?

The appearance of inclusions varies depending on what they contain and whether or not they have an envelope. They store substances the cell eventually uses.

What types of protein are found in the cell membrane?

The cell membrane contains structural and globular proteins. Globular proteins include integral and peripheral proteins.

3-2 Name the three structures that all mammalian cells possess.

The cell membrane, the cytoplasm (which includes cytosol and organelles), and the nucleus

What is the centrosome and what important roles does it play in the life of the cell?

The centrosome is a critical region in the cytoplasm adjacent to the nucleus. It is the site where microtubules are constructed and demolished. The centrosome includes centrioles, pericentriolar material, and asters. Microtubules are the thickest and strongest fibers in the cell and form the "zip-line"-like cables in the cytoskeleton that transport organelles and other intracellular structures from one place to another inside the cell. They also help form the spindle fibers during cell division and are a central part of cilia and flagella.

What is the cytoskeleton and what is its function?

The cytoskeleton is a three-dimensional frame for the cells that is neither rigid nor permanent. It is a flexible, fibrous structure that changes in accordance with the activities of the cell. The cytoskeleton gives support and shape to the cell and enables it to move, provides direction for metabolic activity, and anchors the organelles.

Describe the series of events that scientists believes led to the formation of the first cells on earth.

The first cells are thought to have evolved in the massive oceans of our primitive Earth about 3 billion years ago. Jolted by the fierce electrical energy from frequent lightning storms and by the intense, unabated radiation from the sun, the three molecules (methane gas [CH4], water [H2O], and ammonia [NH3]) that made up the primitive atmosphere were forced to collide and split apart. The first organic molecules, similar to amino acids, are thought to have formed in this tempestuous environment. Clustering into heavy droplets, these molecules are believed to have been washed by driving rains from the atmosphere into the warm, shallow seas below. There, proteins, lipids, and carbohydrates evolved and arranged themselves over time into sophisticated, organized structures—the first cells.

what is the glycocalyx and what important role does it play in cellular interaction?

The glycocalyx is a "sugar coating" on the outside of the cell; it is made of glycoprotein and glycolipid molecules. Similar to the stripes on zebras or the fingerprints on human hands, each glycocalyx is unique. It provides improved cell-to-cell adhesion and represents an important biologic marker for intercellular recognition and for the interactions between the cell and antibodies and the cell and viruses.

How does each of these organelles function within the cell?

The mitochondrion produces 95% of the energy that fuels cellular activity. The energy is predominantly stored in the terminal phosphate bond of adenosine triphosphate (ATP) molecules. The ATP is derived from an array of biochemical processes using oxygen and nutrient molecules. Oxygen enters the body via respiration, and nutrient molecules are provided from food sources. Remarkably, mitochondria contain their own DNA, which includes the instructions for making the enzymes used to make ATP. The ribosome is the site of protein synthesis. Soluble protein intended for intracellular use is manufactured on free-floating ribosomes found throughout the cytosol, whereas protein intended for export outside the cell is synthesized on fixed ribosomes found on the rough endoplasmic reticulum (RER). Newly manufactured molecules of protein are moved internally into passageways in the RER known as cisternae, Latin for "reservoirs." Here the proteins are modified before being moved on to the Golgi apparatus for further modification and packaging. The membrane of the RER is an extension of the outer nuclear membrane, so that RER is often found near the nucleus. Smooth ER, which is connected to rough ER, is active in the synthesis and storage of lipids, particularly phospholipids and steroids, and is therefore seen in large quantities in gland cells. In liver cells smooth ER may also function to eliminate drugs and break down glycogen into glucose. The Golgi apparatus acts as a modification, packaging, and distribution center for molecules destined for either secretion or intracellular use. It also functions in polysaccharide synthesis and in the coupling of polysaccharides to proteins (glycoproteins) on the cell surface. The lysosome's principal responsibilities are the breakdown of nutrient molecules into usable smaller units and the digestion of intracellular debris. Lysosomes may also release their enzymes outside the cell to assist with the breakdown of extracellular material. In addition, lysosomal digestion is responsible for decreasing the size of body tissues (for example, shrinkage of the uterus after parturition and atrophy of muscles in paralyzed animals). Peroxisomes are commonly found in liver and kidney cells and are important in the detoxification of various molecules. Peroxisomes contain enzymes that use oxygen to detoxify a number of harmful substances, including alcohol and formaldehyde. They also assist in the removal of free radicals, which are normal products of cellular metabolism that can be harmful to the cell in large quantities because they interfere with the structures of proteins, lipids, and nucleic acids. Proteasomes are minute structures that consume individual, often misfolded proteins and digest them. They are found throughout the cytosol. Vaults are tiny, hollow transport complexes that are thought to attach to fibers in the cytoskeleton that enable rapid movement from one part of the cell to another. Vaults are able to open up and may lock into nuclear pore complexes on the nucleus, where they may pick up and drop off molecules.

Describe the nuclear in the hello. How does it differ from the cell membrane?

The nuclear envelope is composed of a lipid bilayer. The outer layer of the nuclear envelope is continuous with the endoplasmic reticulum. More than 10% of the nuclear surface consists of nuclear pore complexes—places where the two layers of the nuclear envelope have fused to form a channel. Although the nuclear envelope is similar in structure and composition to the cell membrane, passage of molecules into the nucleus is less selective because the nuclear pore complexes are relatively large (0.1 nm in diameter).

What is the significance of the nucleolus? What happens in that region of the nucleus?

The nucleoli are regions in the nucleoplasm where there are accumulations of ribosomal RNA (rRNA) and collections of ribosomal subunits. Each ribosome is composed of two different subunits. These ribosomal subunits are exported separately from the nucleus and assembled in the cytoplasm to form functional ribosomes. In addition, nucleoli contain the DNA needed to synthesize rRNA.

Why is the nucleus considered the "CEO of operations"?

The nucleus is considered the "CEO of operations" because its primary function is to house the inherited instructions for making all of the protein needed by the organism. The type of enzyme produced by the cell determines its metabolic activities and function. The hereditary information (DNA) is duplicated prior to cell division so that each daughter cell is given an identical copy of the instructions to make all of the types of protein needed by the cell.