Biology - The Cell
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- What is the fundamental unit of all living things?
- The cell
- When was the cell discovered or studied in detail?
- In the 17th century
- Why did it occur then?
- Because of the invention of the microscope
- What is the Cell Theory?
- It is the unifying theory of what a cell is
- What are the four parts of the Cell Theory?
- All living things are composed of cells. The cell is the basic functional unit of life. Cells arise only from pre-existing cells. Cells carry genetic information in the form of DNA. This genetic material is passed from parent cell to daughter cell
- What are three tools available to study the cell and its structures?
- Microscopy, autoradiography, and centrifugation
- What is the most basic tool that scientists use?
- The microscope
- What is magnification?
- An increase in apparent size of an object
- What is resolution?
- The differentiation of two closely situated objects
- What is a compound light microscope?
- It is one that uses two lenses or lens systems to magnify an object
- What is the total magnification equal to?
- It is equal to the product of the eyepiece magnification (usually 10x) and the magnification of the selected objective lens (usually 4x, 10x, 20x, or 100x)
- What are the 3 chief components of the microscope?
- The diaphragm, the course adjustment knob, and the fine adjustment knob
- What does the diaphragm do?
- It controls the amount of light passing through the specimen
- What does the course adjustment knob do?
- It roughly focuses the image
- What does the fine adjustment knob do?
- It sharply focuses the image
- What is the compound light microscope generally used to observe?
- Nonliving specimens
- What does light microscopy require that results in cell death?
- It requires contrast between cells and cell structures
- How is this contrast obtained?
- Through staining techniques
- What is an example of this?
- The dye hematoxylin reveals the distribution of DNA and RNA within a cell due to its affinity for negatively charged molecules
- What is a phase contrast microscope?
- It is a special type of light microscope that permits the study of living cells
- What is used to produce the contrast between cellular structures?
- Differences in refractive index
- What benefit does this provide to the scientist?
- It does not kill the specimen
- How does an electron microscope work?
- It uses a beam of electrons to allow a thousand fold higher magnification than is possible with light microscopy
- Why is the examination of living specimens not possible with electron microscopy?
- Tissues must be fixed and sectioned, and sometimes stained with solutions of heavy metals
- What is autoradiography?
- It is a technique that uses radioactive molecules to trace and identify cell structures and biochemical activity
- How does this work?
- Cells are exposed to a radioactive compound for a brief, measured period of time
- Then what happens to the cells?
- They are incubated, fixed at various intervals and processed for microscopy
- What is each preparation covered with?
- A film of photographic emulsion
- What are environmental requirements for autoradiography?
- The preparations must be kept in the dark for several days while the radioactive compound decays
- What happens then?
- The emulsion is developed; dark silver grains reveal the distribution of radioactivity within the specimen
- What can autoradiography be used for?
- It can be used to study protein synthesis; labeling amino acids with radioactive isotopes allows the pathways of protein synthesis to be examined
- What is differential centrifugation?
- It is the type used to separate cells or mixtures of cells without destroying them in the process
- What happens to them at lower speeds?
- The mixtures separate into layers on the basis of cell type
- What do spinning fragmented cells at high speeds do?
- It causes their components to sediment at different levels in the test tube based upon their respective densities
- What happens to ribosomes when this occurs?
- They go to the bottom of the test tube
- What happens to mitochondria?
- They go to the top
- What happens to lysosomes?
- They go to the top
- What are the two groups of cells?
- Prokaryotic and eukaryotic
- What are viruses?
- They are obligate intracellular parasites
- Are they considered cells?
- No
- Why not?
- They are not capable of living independently
- What are some types of prokaryotes?
- Bacteria and cyanobacteria
- Are they unicellular or multicellular?
- They are unicellular organisms
- Do they have simple or complex structures?
- Simple structures
- Do prokaryotic cells have an outer cell membrane?
- Yes
- Do they have membrane bound organelles?
- They do not contain any membrane bound organelles
- Do they have a nucleus?
- They do not have a nucleus
- Where is their genetic material then?
- It consists of a singular circular molecule of DNA concentrated in an area of the cell called the nucleoid region
- What else may there be dealing with genetic material?
- There may be smaller rings of DNA called plasmids
- How many genes do plasmids have?
- Just a few genes
- How do plasmids replicate?
- They replicate independently of the main chromosomes
- What kinds of genes do they often contain?
- Genes that allow the prokaryote to survive adverse conditions
- Do bacteria have a cell wall?
- Yes
- Do they have a cell membrane?
- Yes
- Do they have cytoplasm?
- Yes
- Where does respiration occur for bacteria?
- At the cell membrane
- All multicellular organisms and all nonbacterial unicellular organisms are composed of what?
- Eukaryotic cells
- What is a typical eukaryotic cell bound by?
- A cell membrane and contains cytoplasm
- What does cytoplasm contain?
- Organelles
- What are organelles suspended in?
- A semi fluid medium called the cytosol
- Where is the genetic material in all this?
- The material consists of linear strands of DNA organized into chromosomes and located within a membrane-enclosed organelle called the nucleus
- What do plants have that animal cells don’t?
- They have a cell wall and chloroplasts
- What do animal cells that plant cells don’t?
- They have centrioles
- Where are centrioles located?
- In the chromosome area
- What is cytosol?
- The fluid component of the cytoplasm
- What does it consist of?
- An aqueous solution containing free proteins, nutrients, and other solutes
- What is the cytoskeleton?
- It is composed of microtubules, microfilaments, and intermediate fibers, and other accessory proteins, is also found in the cytosol
- What do these proteinaceous filaments do?
- They give the cell its shape and anchor the organelles
- What else do they do?
- They function in cell maintenance and aid in intracellular transport
- What does the cell membrane do?
- It surrounds the cell and regulates the passage of materials in both directions
- What does the cell membrane exhibit that deals with the movement of things into and out of the cell?
- It exhibits selective permeability
- What is the fluid mosaic model?
- It is the generally accepted model of what the cell membrane is.
- What does it say?
- It says that the cell membrane consists of a phospholipids bilayer with proteins embedded throughout
- What are phospholipids?
- They have a hydrophilic or polar phosphoric acid region and a hydrophobic nonpolar fatty acid region
- In a lipid bilayer, where is the hydrophilic region found?
- It is found on the exterior surfaces of the membrane
- Where are the hydrophobic regions found?
- They are found in the interior of the membrane
- Where are cholesterol molecules in this?
- They are embedded in the hydrophobic interior
- What do they do?
- They are involved in cell movement as well as support
- Where are proteins in this?
- They are interspaced throughout the membrane and may be partially or completely embedded in the bilayer
- What are transport proteins?
- They are membrane spanning molecules that allow certain ions and polar molecules to pass through the lipid bilayer
- What are cell adhesion molecules?
- CAMs are proteins that contribute to cell recognition and adhesion, and are particularly important during development
- What are receptors?
- They are complex proteins or glycoproteins generally imbedded in the membrane with sites that bind to specific molecules in the cell’s external environment
- What is pinocytosis?
- It is the ingestion of fluids or small particles
- What is the alternative way the receptor helps out?
- It may signal across the membrane and into the cell via a second messenger
- Is the plasma membrane readily permeable?
- Yes
- What can go through?
- Small nonpolar molecules such as oxygen and small polar molecules such as water
- How can small charged molecules cross?
- They are usually able to cross the plasma membranes through protein channels in the membrane
- How do larger charged molecules cross the membrane?
- They cross with the assistance of carrier proteins
- What is the nucleus?
- It controls the activities of the cell, including cell division
- What is it surrounded by?
- A nuclear membrane or envelope
- Is it double or single layered?
- It is a double membrane that maintains a nuclear environment distinct from that of the cytoplasm
- What are interspersed throughout the nuclear membrane?
- Nuclear pores
- What does the nucleus contain?
- It contains the DNA
- What is the DNA complexed with?
- Structural proteins called histones
- What do they form together?
- Together they form chromosomes
- What is the nucleolus?
- It is the dense structure in the nucleus where ribosomal RNA synthesis occurs
- What are ribosomes?
- They are sites if protein production and are synthesized by the nucleolus
- What do ribosomes consist of?
- They consist of two subunits, one large and one small
- What is each subunit composed of?
- It is composed of rRNA and proteins
- What are free ribosomes?
- They are ribosomes found in the cytoplasm
- What are bound ribosomes?
- They line the outer membrane of the endoplasmic reticulum
- What is the endoplasmic reticulum?
- It is a network of membrane-enclosed spaced connected at points with the nuclear membrane
- What are ER with ribosomes lining its outer surface known as?
- They are known as rough ER
- What are ER without ribosomes known as?
- They are known as smooth ER
- What is ER involved with generally?
- Generally, ER is involved with the transport of materials throughout the cell
- What types of materials are really used by the ER?
- Materials destined to be secreted from the cell
- What is smooth ER involved in?
- They are involved with lipid synthesis and the detoxification of drugs and poisons
- What is rough ER involved in?
- It is involved in protein synthesis
- Proteins synthesized by the bound ribosomes do what?
- They cross into the cisternae of the RER
- What happens there?
- They undergo chemical modification
- What happens to them then?
- Then they cross into the smooth ER, where they are secreted into cytoplasmic vesicles and are transported to the Golgi apparatus
- What is the Golgi apparatus?
- It consists of a stack of membrane-enclosed sacs
- What does it do?
- It receives vesicles and their contents from smooth ER, modifies them through glycosylation, repackages them into vesicles, and distributes them
- What is the Golgi active in the distribution of?
- Newly synthesized materials to the cell surface
- What are secretory vesicles?
- They are produced by the Golgi, and they release their contents to the cell’s exterior by the process of exocytosis
- What are vesicles and vacuoles?
- They are membrane-bound sacs involved in the transport and storage of materials that are ingested, secreted, processed, or digested by the cell
- Which of the two are bigger?
- Vacuoles are bigger than vesicles
- Which are more likely to be found in plant cells?
- Vacuoles
- What are lysosomes?
- They are membrane-bound vesicles that contain hydrolytic enzymes involved in intracellular digestion
- What is the effective pH level?
- 5
- What does this imply?
- It implies they have to be enclosed within the lysosome
- What is the lysosome?
- It is an acidic environment distinct from the neutral pH of the cytosol
- What else do lysosomes do?
- They aid in renewing a cell’s own components by breaking down the old ones and releasing their molecular building blocks into the cytosol for reuse
- How can a cell commit suicide?
- It can rupture its lysosome membrane and release its hydrolytic enzymes
- What is this referred to as?
- Autolysis
- What are microbodies?
- They are membrane-bound organelles specialized as containers for metabolic reactions
- What are two important types of microbodies?
- Peroxisomes and glyoxysomes
- What do peroxisomes do?
- They contain oxidative enzymes that catalyze a class of reactions in which hydrogen peroxide is produced by the transfer of hydrogen from a substrate to oxygen.
- What do peroxisomes do to fats?
- They break them down into smaller molecules that can be used for fuel
- What else?
- They can be used in the liver to detoxify compounds harmful to the body, such as alcohol
- What are they used for in seedlings?
- They convert fats into sugars until it is mature enough to produce its own sugars through photosynthesis
- What are mitochondria?
- They are the sites of aerobic respiration within the cell and hence are the suppliers of energy
- What is each mitochondrion bound by?
- They all have an outer and inner phospholipids bilayer membrane
- What does the outer membrane do?
- It is smooth and acts as a sieve, allowing molecules through on the basis of size
- What is the area between the inner and outer membrane known as?
- It is known as the intermembrane space
- What does the inner membrane have inside it?
- It has many convolutions called cristae and a high protein content that includes the proteins of the electron transport chain
- What is the area bounded by the inner membrane?
- It is known as the mitochondrial matrix
- What is the site of?
- It is the site of many of the reactions in cell respiration
- How are mitochondria different from other organelles?
- They are semiautonomous, which means they contain their own DNA which is circular and ribosomes
- What does this enable them to do?
- This enables them to self-replicate by binary fission and produce some of their own proteins
- What were mitochondria believed to be a long time ago?
- They were believed to have been early prokaryotic cells that evolved a symbiotic relationship with the ancestors of eukaryotic cells
- What are chloroplasts?
- They are plastid found only in algal and plant cells
- What do they contain?
- They contain chlorophyll
- What are they the site of?
- Photosynthesis
- What do chloroplasts contain, and what are they similar to?
- They contain their own DNA and ribosomes, and exhibit the same semi autonomy as mitochondria
- What is a cell wall?
- A tough outer cell wall that protects the cell from external stimuli and desiccation
- What has cell walls?
- Plant cells have a cell wall composed of cellulose
- What else has them?
- Fungi have a cell wall composed of chitin and other materials
- Do animals have a cell wall?
- No they do not
- What are centrioles?
- They are a specialized type of microtubule involved in spindle organization during cell division
- What is different about them than other organelles?
- They are not membrane bound
- How many centrioles do animal cells have?
- They usually have a pair of centrioles that are oriented at right angles to each other
- Where do they lie?
- In a region called the centrosome
- Do plant cells have centrioles?
- They do not contain centrioles
- What does the cytoskeleton do?
- It gives the cell mechanical support, maintains its shape, and functions in cell motility
- What is it composed of?
- Microtubules, microfilaments, and intermediate filaments
- What are microtubules?
- They are hollow rods made up of polymerized tubulins that radiate throughout the cell
- What is composed of microtubules?
- Examples are centrioles, which direct the separation of chromosomes during cell division
- What are cilia and flagella?
- They are specialized arrangements of microtubules that extend from certain cells and are involved in cell motility
- What are microfilaments?
- They are solid rods of actin
- What uses microfilaments?
- Muscle contraction does
- What else do microfilaments do?
- They move materials across the plasma membrane, and in amoeboid movement
- What are intermediate filaments?
- They are a collection of fibers involved in maintenance of cytoskeletal integrity
- How thick are they?
- Their diameters fall between those of microtubules and microfilaments
- What is simple diffusion?
- It is the net movement of dissolved particles down their concentration gradients
- Which direction does it go?
- From a region of higher concentration to a region of lower concentration
- Is this an active or passive process?
- It is a passive process
- What is osmosis?
- It is the simple diffusion of water from a region of lower solute concentration to a region of higher solute concentration
- What happens when the cytoplasm of the cell has a lower solute concentration than that of the extracellular medium?
- The medium is said to be hypertonic to the cell and water will flow out, causing the cell to shrink
- What happens when the cytoplasm of a cell has a higher solute concentration than the extracellular medium?
- The medium is said to be hypotonic to the cell and water will flow in
- What does this cause the cell to do?
- It causes it to swell
- What happens if too much water flows in?
- It causes it to lyse
- What is it called when the solute concentrations inside and outside the cell are equal?
- The cell and medium are said to be isotonic
- What is facilitated diffusion?
- It is the passive transport of dissolved particles down their concentration gradient with the help of carrier molecules
- Does it require energy?
- No
- What is active transport?
- It is the net movement of dissolved particles against their concentration gradient with the help of transport proteins
- Does this require energy?
- Yes
- What is active transport needed for?
- It is required to maintain membrane potentials in specialized cells such as neurons
- What is endocytosis?
- It is a process in which the cell membrane invaginates
- What does this form?
- It forms a vesicle that contain extracellular medium
- What is phagocytosis?
- It is the engulfing of large particles
- What is exocytosis?
- In exocytosis, a vesicle within the cell fuses with the cell membrane and releases its contents to the outside
- What is an important thing to note about these two things pertaining to the membrane?
- In neither of these does the transported material actually cross the membrane
- What are the four types of tissue?
- Epithelial, connective, nervous, and muscle
- What is epithelial tissue?
- It covers the surfaces of the body and lines the cavities, protecting them against injury, invasion, and desiccation
- What is epithelium involved with?
- Absorption, secretion, and sensation
- What is connective tissue?
- It is involved with body support and other functions
- What are some specialized connective tissues?
- Bone, cartilage, tendons, ligaments, adipose tissue, and blood
- What is nervous tissue?
- It is composed of specialized cells called neurons that are involved with perception, processing, and storage of information concerning internal and external environments
- What is muscle tissue?
- It has great contractile capability and is involved in body movement
- What are the three types of vertebrate muscle?
- Cardiac muscle, skeletal muscle, and smooth muscle
- What are the sizes of viruses?
- They range from 20 nanometers to 300 nanometers
- How big are prokaryotes?
- 1 micrometer to 10 micrometer
- How big are eukaryotic cells?
- They are 10 micrometers to 100 micrometers
- How is viral DNA?
- Either linear or circular, and has been found in four-varieties
- What are the four types?
- Single-stranded DNA, double-stranded DNA, single-stranded RNA, and double-stranded RNA
- What is the protein coat also known as?
- The capsid
- What is it comprised of?
- Many protein subunits and may be enclosed by a membranous envelope
- What does this mean?
- It means they can express their genes and reproduce only within a living host cell
- Why is that?
- Because they lack the structures necessary for independent activity and reproduction
- What are viruses called that exclusively infect bacteria?
- Bacteriophages
- Does the phage capsid enter the cell?
- No