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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?
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?
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?
Do they have a cell membrane?
Do they have cytoplasm?
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?
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?
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?
What are lysosomes?
They are membrane-bound vesicles that contain hydrolytic enzymes involved in intracellular digestion
What is the effective pH level?
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?
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?
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?
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?
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?
Does the phage capsid enter the cell?

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