Cell Structure and Function

Cell Structure

• Body is composed of basic building blocks.
• These building blocks are cells.
• Epithelial cells protect the body’s surface.
• Bone cells support the body.
• Immune cells fight bacteria.
• Blood cells carry nutrients and oxygen.
• Fundamental characteristics are shared by all cells.
• The cell is the smallest unit of something living.
• An organism is a living thing made of one or many cells.
• Cells are the building blocks of all organisms.
• Tissues are cells of one kind interconnecting and performing a shared function.
• Organs are tissues combining.
• Organ systems are organs making up the system.
• An organism is multiple systems functioning together.
• Cells are grouped into prokaryotic and eukaryotic.
• A biologist studies cells for research.

Studying Cells

• Microscopes magnify objects.
• Micrographs are microscope photographs of cells.
• The image’s orientation changes from microscope lenses.
• Microscopes use two sets of lenses to magnify the image.
• Light microscopes use visible light passing through lenses to see a specimen.
• Light microscopes magnify up to 400 times.
• Magnification enlarges an object’s appearance.
• Resolving power distinguishes two adjacent structures separately.
• Clarity and detail is better with higher resolution.
• Magnification is 1,000 times with oil immersion lenses.
• Electron microscopes use an electron beam.
• This allows for higher magnification with more detail.
• Electron microscopes have higher resolving power.
• Specimens are killed to be viewed in an electron microscope.
• Electrons move best in a vacuum due to short wavelengths.
• A scanning electron microscope moves electrons across a cell's surface.
• Scanning electron microscopes create cell surface details.
• Transmission electron microscopes penetrate cells.
• Transmission electron microscopes provide details of cell internal structures.
• Electron microscopes are bulky and expensive.

Cell Theory

• Antony van Leeuwenhoek was a Dutch shopkeeper who crafted lenses in the 1600’s.
• Van Leeuwenhoek observed protista and sperm, which he called "animalcules".
• Robert Hooke coined "cell" in Micrographia in 1665 for box-like structures in cork tissue.
• Van Leeuwenhoek discovered bacteria and protozoa in the 1670’s.
• Matthias Schleiden and Theodor Schwann proposed the unified cell theory in the late 1830’s.
• All organisms have one or more cells.
• Cell is the basic unit of life.
• New cells come from existing cells.
• Rudolf Virchow contributed to this theory later on.

Cytotechnologist Job

• Cytotechnologists study cells via microscopes and lab tests.
• They determine normal vs. abnormal cellular changes.
• Cytotechnologists study specimens from all organs.
• They consult a pathologist when abnormalities are observed.
• Cytotechnologists help save lives.
• Chances of success increase with early abnormality discovery.

Prokaryotic Cells

• Bacteria and Archaea are classified as prokaryotes.
• Animals, plants, fungi, and protists cells are eukaryotes.

Components of Prokaryotic Cells

• A plasma membrane is an outer covering separating the cell's interior.
• Cytoplasm has a jelly-like cytosol in which other components are found.
• DNA is the cell’s genetic material.
• Ribosomes synthesize proteins.
• Prokaryotes lack a nucleus or membrane-bound organelles.
• Prokaryotic DNA is found in the nucleoid.
• Most have a peptidoglycan cell wall and polysaccharide capsule.
• The cell wall protects, maintains shape, and prevents dehydration.
• Capsules attach the cell to surfaces.
• Flagella are used for locomotion.
• Pili exchange genetic material.
• Fimbriae are used by bacteria to attach to a host cell.

Microbiologist Career

• Microbiologists are scientists who study microbes.
• Washing hands prevents the spread of contagious illnesses.
• Most microbes are beneficial.
• Some microbes in the gut make vitamin K.
• Microbes are used to ferment beer and wine.
• Microbiologists can pursue careers in the food, veterinary, medical, and pharmaceutical industries.
• Environmental microbiologists remove pollutants using microbes in bioremediation technologies.
• Bioinformatics provides computer models of bacterial epidemics.

Cell size

• Prokaryotic cells are 0.1 to 5.0 m in diameter.
• Eukaryotic cells range from 10 to 100 m.
• Ions and molecules diffuse quickly to other parts of smaller prokaryotic cells.
• Wastes also diffuse out quickly.
• There are different structural adaptations in eukaryotic cells to enhance intracellular transport.
• Surface area increases by the square of the radius.
• Volume increases as the cube of the radius.
• A cell’s surface area-to-volume ratio decreases as it increases in size.
• Plasma membrane will not have enough surface area for the increased volume if a cell grows too large.
• It becomes less efficient as the cell grows.
• One way to become efficient is to divide; the other is to develop organelles.
• Eukaryotic cells are more sophisticated as a result of organelle development.

Eukaryotic Cells

• A philosophy in architecture is that buildings should be built to support activities inside them.
• The natural world follows that form, especially in cell biology.
• Eukaryotic cells have organelles.
• Organelles are membrane-bound nucleus and compartments/sacs which have specialized functions.
• Nucleus is surrounded by a membrane.
• Organelle means "little organ".
• Organelles allow compartmentalization in different areas of the cell.

Plasma membrane

• Phospholipid bilayer with proteins separates internal contents from the environment.
• A phospholipid is a lipid molecule with two fatty acid chains and a phosphate-containing group.
• The plasma membrane controls molecules and ion passage.
• Wastes also pass through the membrane.
• Microvilli are fingerlike projections in plasma membranes of cells that specialize in absorption.
• Microvilli line the small intestine, absorbing nutrients from digested food.
• People with celiac disease cannot absorb nutrients due to damaged microvilli.
• They must follow a gluten-free diet.

Cytoplasm

• The cytoplasm is the region between the plasma membrane and the nuclear envelope.
• It is made of organelles suspended in gel-like cytosol, the cytoskeleton, and various chemicals.
• The cytoplasm is 70-80% water.
• It has a semi-solid consistency from proteins within it.
• There are organic and inorganic molecules found
• Turgor pressure is in the liquid inside the central vacuole in plant cells.

Nucleus

• The nucleus is the most prominent organelle in a cell.
• The nucleus houses DNA and directs ribosome and protein synthesis.
• The nuclear envelope is the nucleus's double-membrane structure.
• There is an inner and outer membrane, both with phospholipid bilayers.
• Pores control the passage of ions, molecules, and RNA.
• Nucleoplasm is the semi-solid fluid inside the nucleus.

Chromatin and Chromosomes

• Chromosomes are structures of DNA, the hereditary material.
• DNA is organized in a single circular chromosome in prokaryotes.
• Chromosomes are linear structures in eukaryotes.
• Each eukaryotic species has a specific number of chromosomes.
• Chromosomes are visible when the cell is dividing.
• Proteins attach to chromosomes during growth and maintenance in the life cycle.
• The combination in this state is called chromatin.

Nucleolus

• The nucleus directs the synthesis of ribosomes.
• Some chromosomes have sections of DNA that encode ribosomal RNA.
• The nucleolus aggregates the ribosomal RNA with associated proteins.
• This assembles the ribosomal subunits and moves them out to the cytoplasm.

Ribosomes

• Ribosomes synthesize protein.
• Ribosomes appear in clusters (polyribosomes) or single dots that float freely in the cytoplasm when viewed through a microscope.
• Ribosomes may be attached to the plasma membrane or endoplasmic reticulum's cytoplasmic side.
• Large complexes of protein and RNA make-up ribosomes.
• The complexes consists of 2 subunits: large and small.
• Messenger RNA (mRNA) is transcribed from DNA in the nucleus and then ribosomes receive their protein synthesis "orders".
• Ribosomes translate the code from the nitrogenous bases sequence in the mRNA into a specific amino acid order in a protein.
• Amino acids are building blocks of proteins.

Mitochondria

• Mitochondria are the "powerhouses".
• They are responsible for making adenosine triphosphate (ATP).
• ATP is the cell's main energy-carrying molecule.
• Cellular respiration produces ATP from glucose.
• Oxygen is used and carbon dioxide is produced.
• Muscle cells have a high concentration of mitochondria that produce ATP.
• When cells don't get enough oxygen, they produce lactic acid instead.
• Mitochondria are oval-shaped, double membrane organelles.
• They contain ribosomes and DNA.
• Membranes are phospholipid bilayers embedded with proteins.
• The inner layer has folds called cristae.
• The mitochondrial matrix is the area surrounded by the folds.
• Cristae and the matrix have different roles in cellular respiration.

Peroxisomes

• Small, round organelles enclosed by single membranes.
• Peroxisomes carry out oxidation reactions that break down fatty acids and amino acids.
• They also detoxify poisons.
• Oxidation reactions release hydrogen peroxide (H2O2).
• Enzymes safely break down the H2O2 into oxygen and water.
• The alcohol liver cells detoxify is an example.
• Glyoxysomes are specialized peroxisomes in plants.
• They are responsible for converting stored fats into sugars.

Vesicles and Vacuoles

• Vesicles and vacuoles are membrane-bound sacs that function in storage and transport.
• Vacuoles are larger.
• Vesicle membranes fuse with either the plasma membrane or other membrane systems.
• Some agents break down macromolecules in vacuoles.
• Vacuole membranes do not fuse with other membranes.

Animal vs Plant Cells

• Each eukaryotic cell has a plasma membrane, cytoplasm, a nucleus, ribosomes, mitochondria, peroxisomes, and vesicles and vacuoles.
• Animal cells have microtubule organizing centers (MTOCs) with centrioles called the centrosome.
• Animal cells have a centrosome and lysosomes
• Plant cells have a cell wall, chloroplasts, specialized plastids, and a large central vacuole.

Centrosome

• The centrosome organizes microtubules near the nuclei of animal cells.
• It contains two centrioles that lie perpendicular to one another.
• Each centriole is a cylinder of nine triplets of microtubules.
• The centrosome replicates itself before cell division.
• Centrioles have a role in pulling duplicated chromosomes to opposite ends.
• The centrioles exact function in cell division isn't clear.

Lysosomes

• Animal cells have lysosomes.
• Lysosomes are the cell's "garbage disposal."
• Digestive processes take place in vacuoles in plant cells.
• Enzymes within lysosomes break down proteins, polysaccharides, lipids, nucleic acids, and organelles.
• These enzymes are active at a much lower pH.
• Cytoplasm reactions could not occur at a low pH.

Cell Wall

• The cell wall is external to the plasma membrane.
• The cell wall protects the cell, supports structural, and gives the cell shape.
• Fungal and protistan cells also have cell walls.
• Plant cell walls are cellulose based.

Chloroplasts

• Chloroplasts have their own DNA and ribosomes.
• Chloroplasts are plant cell organelles that conduct photosynthesis.
• Photosynthesis makes glucose and oxygen using carbon dioxide, water, and light energy.
• Plants (autotrophs) make their own food.
• Animals (heterotrophs) must ingest food.
• Chloroplasts have two membranes.
• Thylakoids are interconnected and stacked fluid-filled membrane sacs.
• Granum is the stack of thylakoids.
• Stroma is the fluid enclosed by the inner membrane.
• Photosynthesis light harvesting reactions occur in the thylakoid membranes.
• Sugar synthesis happens in the fluid inside the inner membrane (stroma).
• Chloroplasts have their own genome on a single circular chromosome.
• Chloroplasts contain chlorophyll, which is a green pigment that captures light energy for photosynthetic reactions.
• Like plant cells, photosynthetic protists have chloroplasts.
• Some bacteria conduct photosynthesis, but their chlorophyll isn't in an organelle.

Endosymbiosis

• Mitochondria and chloroplasts contain DNA and ribosomes
• Symbiosis is organisms from two species depending on each other for survival.
• Endosymbiosis is a mutually beneficial relationship with one organism inside the other.
• Microbes that produce vitamin K live inside the human gut
• The microbes get food and protection and humans get vitamin K.
• Bacteria, mitochondria, and chloroplasts are all similar.
• Bacteria, mitochondria, and chloroplasts all have DNA and ribosomes.
• Scientists believe host cells and bacteria formed an endosymbiotic relationship when the host ingested both aerobic and autotrophic bacteria (cyanobacteria) but did not destroy them.
• Through millions of years of evolution, the ingested bacteria became more specialized for their functions. Aerobic bacteria became mitochondria and autotrophic bacteria became chloroplasts.

Central Vacuole

• Vacuoles are essential to plant cells.
• Plant cells each have a central vacuole that takes up most of the area of the cell.
• The central vacuole regulates the cell's water concentration.
• If a plant isn’t watered for several days, it wilts
• Water in the soil becomes lower than in the plant, the central vacuoles and cytoplasm release water.
• The cell walls do not have support when the central vacuole shrinks, resulting in the plant wilting.
• The central vacuole also supports cell expansion, cell gets larger when central vacuole holds more water.

Endomembrane System

• A group of membranes and organelles in eukaryotic cells that works to modify, package, and transport lipids and proteins.
• The endomembrane system includes the nuclear envelope, lysosomes, vesicles, the ER, and the Golgi apparatus.
• Though not technically within the cell, the plasma membrane interacts with the system.
• The endomembrane system does not include themembranes of either mitochondria or chloroplasts.

Endoplasmic Reticulum

• A series of interconnected membranous sacs and tubules which modifies proteins and synthesizes lipids.
• These two functions happen in separate areas of the ER: the rough ER and the smooth ER.
• The hollow ER tubules portion is called the lumen or cisternal space.
• The ER’s phospholipid bilayer membrane is continuous with the nuclear envelope.
• Ribosomes attached to the cytoplasmic surface give the rough endoplasmic reticulum (RER) its name due to a studded appearance when viewed through an electron microscope.
• Ribosomes transfer newly synthesized proteins into the RER lumen.
• The proteins undergo structural modifications, e.g. folding or side chains.
• These modified proteins may be put in the the ER or other organelles' membranes or secreted from the cell.
• The RER also makes phospholipids for cellular membranes.
• Transport vesicles bud from the RER’s membrane if the phospholipids or proteins are not destined to stay.
• You can assume the RER is abundant in cells that secrete proteins, e.g. liver cells.

Smooth ER

• The Smooth Endoplasmic Reticulum (SER) has few or no ribosomes on its cytoplasmic surface, but is continuous with the RER.
• Functions of the SER:
  • Synthesis of carbohydrates, lipids, and steroid hormones
  • Detoxification of medications and poisons
  • Storage of calcium ions
• In muscle cells, the sarcoplasmic reticulum is a specialized SER.
• They are responsible for storage of the calcium ions needed to trigger coordinated contractions of muscle cells.

Cardiologist Career

• Heart disease is the leading cause of death in the US.
• Heart failure means the heart can't pump enough oxygenated blood.
• Untreated heart failure leads to kidney and organ failure.
• The heart walls are made of cardiac muscle tissue.
• Heart failure means endoplasmic reticula of cardiac muscle cells don't function properly.
• Insufficient calcium ions cause insufficient contractile force.
• Cardiologists are doctors who specialize in treating heart diseases, including heart failure.
• They can diagnose heart failure via physical exams, EKGs, chest X-rays, and other tests.
• If diagnosed, they prescribe medications and reduce salt intake and exercise.

Golgi Apparatus

• Vesicles bud from the ER and transport their contents elsewhere.
• Lipids or proteins within transport vesicles are sorted, packaged, and tagged.
• Sorting, tagging, packaging, and distribution of lipids and proteins occurs in the Golgi apparatus.
• The Golgi is a series of flattened membranes.
• The cis face (receiving side) of the Golgi apparatus is toward the ER.
• The opposite is the trans face.
• ER-formed transport vesicles travel to the cis face, fuse with it, and empty contents into the lumen of the Golgi apparatus.
• Proteins and lipids travel through the Golgi and make modifications.
• Phosphate groups or molecules tag the newly modified lipids and proteins.
• The molecules can then be routed to their proper destinations.
• Tagged molecules are put into secretory vesicles made from the Golgi trans face.
• Vesicles deposit their contents into other parts of the cell, while other secretory vesicles release contents outside the cell through the plasma membrane.
• Cells that engage in a great deal of secretory activity have an abundance of Golgi. Salivary glands and immune cells are examples.
• The Golgi synthesizes polysaccharides, some are put in the cell wall and others are used elsewhere.

Geneticist Career

• Many diseases arise from genetic mutations that prevent synthesis of critical proteins.
• One example is Lowe disease.
• Lowe disease causes a Golgi apparatus enzyme deficiency.
• A woman can find mutations through prenatal testing.
• Geneticists analyze prenatal tests and counsel results and perform genetic studies for new drugs.

Lysosomes Cont.

• lysosomes use their hydrolytic enzymes to destroy pathogens that come into the cell.
• Macrophages are blood cells known for this.
• Phagocytosis/endocytosis occurs when plasma membrane folds and engulfs a pathogen.
• The invaginated section becomes a vesicle.
• The vesicle bonds with a lysosome before being destroyed.

Cytoskeleton

• A network of protein fibers that maintain cell shape, secure organelles in positions, allow cytoplasm and vesicles to move, and enable cell movement in multicellulars.
• There are three types of cytoskeleton: microfilaments, intermediate filament, and microtubules.
• Microfilaments are the narrowest protein fibres.
• They are involved in cellular movement.
• The fibers have a diameter of about 7 nm.
• Make of interlaced strands of actin (globular protein).
• Actin are powered by ATP to formulate a filament track for motor proteins.
• Motion, e.g. cell division in animals and cytoplasm streaming in plants.
• Contraction and sliding past each result in motion.
• Microfilaments give shape to rigid cells.
• Microfilaments depolymerize or disassemble to allow motion

Intermediate Filaments.

• This filament is made of fibrous proteins (several stands).
• Diameters between microfilaments and microtubules (8 to 10mn).
• No role in movement and instead function to offer structural support.
• They bear tension forces, maintain cell shapes and secure organelles and nucleus.
• The fiber are highly diverse group in cell skeletons.
• The skin, hair, and nails are made from keratin type protein.

Microtubules

• Microtubule are small tubular cylinders that form the filament’s walls.
• With diameters of about 25 nm offer the largest cytoskeletal component.
• The components helps the cell resist compression, act as vesicles trackers.
• Aids replication of chromosomes to dividing cell ends.
• Fiber dissolve and quickly reform.

Flagella and Cilia

• They can extend from plasma membranes and are to move the cell.
• Sperm are cells that uses singular flagellum to move.
• Cilia tend to cover the membrane and aid moving cells as well.
• Paramecia and ovary lining depend on cilia movement.
• Both contain difference lengths and number however form arrangement with microtubules referred to as 9+2 array.