Chapter 3: Cell Structure Flashcards
What is a cell?
the basic unit of life
What is a microscope?
instruments that produce a magnified image of an object
What is the object in microscopy?
The material place under the microscope, that is being magnified.
What is the image in microscopy?
the magnified appearance of the material viewed under the microscope
What is the magnifcation?
How many times bigger the image is compared to the object.
How do you calculate the magnification?
magnification= image/ object
How many meters in Kilometers?
1x10^(3); 1000
How many metres in a millimetre?
1x10^(-3) ; 0.001
How many meters in a micrometre?
1x10^(-6); 0.000001
How many metres in a nanometre?
1x10^(-9); 0.000000001
What is the rule with the magnification equation?
the image size and object size have to be in the same units
What is the resolution/ resolving power?
the minimum distance apart two objects can be in order for them to appear as separate items
What is the resolving power of a light microscope?
0.2μm
What is the benefit of a greater resolution?
it has a greater clarity making the image produced clearer and more precise
What is Cell fractionation?
the process where cells are broken up and the different organells they contain are separated out.
Why is cell fractionation needed?
to obtain large numbers of isolated organells so the function and structure can be studied.
What solution does tissue have to be placed in before cell fractionation?
a cold, buffered solution of the same water potential.
Why does the solution the tissue is place in for cell fractionation have to be cold?
to reduce enzyme activity that might break down the organells.
Why does the solution the tissue is place in for cell fractionation have to be buffered?
so that the pH doesn’t fluctuate, which could alter the organells structure.
Why does the solution the tissue is place in for cell fractionation have to be the same water potential?
to prevent organells from bursting or shrinking as a result of osmotic gain or loss of water
What are the two stages of cell fractionation?
Homogenation and ultracentrifugation
What is Homogenation?
When the cells are broken up by a homogeniser (blender), releasing organells from the cell resulting homogenate which is filtered to remove debris.
What is ultracentrifugation?
the process by which the fragments in filtered homogenate are separated by a centrifuge.
How does the centrifuge separate the organells in the homogenate?
the centrifuge spins the homogenate at a slow speed, the heaviest organells are forced to the bottom of the tube forming a sediment separate to the remaining fluid (supernatant). the supernatant is separated and spun again at a higher speed.
What is an electron microscope?
a microscope that uses a beam of electrons instead of light
What are the benefits of using an electron microscope?
the electron beam has a short wavelength so has a high resolving power; the electron beam can be focused using electromagnets
What is the resolving power of an electron microscope?
0.1 nm
What are the two types of electron microscope?
The transmission electron microscope (TEM); The scanning electron microscope (SEM)
What does a Transmission electron microscope do?
produces a beam of electrons that is sent through thin parts of the specimen to produce an image.
What is a photomircrograph?
a photograph of the image produced by a microscope
What is the resolving power of the TEM?
0.1nm
What limits the resolving power of the TEM?
must be a vacuum; complex staining process; specimen has to be thin; image could contain an artefact
What is an artefact in microscopy?
something on the slide that is not part of the sample (incorrect specimen preparation)W
What is the main improvement of SEM from TEM?
TEM produces a 2D image, a SEM produces a 3D image.
What does a scanning electron microscope do?
directs a beam of electrons onto the surface of the specimen , where is it passed across it in a regular pattern. this scatters the electrons to show the contour the specimen.
What is the resolving power of the SEM?
20nm (worse than TEM, but better than light microscope)
What is an eyepiece graticule?
a scale etched onto a glass disc in the eyepiece measured, only once it has been calibrated
When does the eyepiece graticule need to be calibrated?
When using it to measure the image at a new magnification.
What is used to calibrate the eyepiece graticule?
a stage micrometer
What is a stage micrometer?
a slide placed on the microscope’s stage, that is used to calibrate the eyepiece graticule
What is the typical size of a stage micrometer?
typically 2mm with sub-divisions 10μm apart
How is the eyepiece graticule calibrated?
the stage micrometer is placed on the stage and lined up with the eyepiece graticule, then the number of units on the graticule scale in one micrometer meter unit is found, the calibration value is then calculated.
What is the calibration value?
the length of each unit on the eyepiece graticule
How is the calibration value calculated?
(units on micrometer * length of each micrometer unit) / amount of units on eyepiece graticule
What is the Ultrastructure of a cell?
the internal structure of a cell that makes it suited to it’s function
How can Eukaryotic cells be recognised?
they have a distinct nucleus and possess membrane-bounded organells
Describe the structure of the nucleus.
a large organelle enclosed by a double membrane (an envelope) perforated by pores. contains Chromosomes and one or more nucleoli. it is about 10-20μm
What is the function of the nucleus?
The chromosomes contain DNA which control the synthesis of protein ribosomes are formed in the nucleolus.
What is the nuclear envelope?
a double membrane that surround the nucleus ( outer is continuous with ER, can have ribosomes on the surface)
What is the purpose of the nuclear pores?
They allow the passage of large molecules out of the nucleus
What is the Nucleoplasm?
the granular, jelly-like material that makes the bulk of the nucleus
What are Chromosomes?
protein bound, linear DNA
What is the Nucleous?
a small spherical region within the nucleoplasm that makes ribosomal RNA and Ribosomes.
Describe the structure of the mitchondrion.
it has a double membrane, with the inner folding to form Cristae. inside it has a matrix containing enzymes, circular DNA and ribosomes.
What is the function of the mitochondria?
the site of aerobic respiration and responsible for producing most of the ATP in a cell.
What are the Cristea in the mitochondria?
extensions of the inner membrane in the mitochondria that provide a large surface area for the attachment of enzymes and other proteins used in respiration.
What is the matrix?
The cytoplasm of the mitochondria that contains proteins, lipids ribosomes and DNA that allow it to produce its own proteins (enzymes) for photosynthesis.
Describe the structure of the Chloroplast.
Surrounded by two membranes. Contains a cytoplasm called a stroma with a system of membranes running through it. these are stacked to form the grana containing chlorophyll. stroma has circular DNA, ribosomes and stanch grains.
What is the function of the chloroplast?
The organelle in which photosynthesis takes place. Pigments capture the energy of sunlight and transfer it to chemical bonds.
What is the chloroplast envelope?
the double plasma membrane around the chloroplast
What are the grana?
stacks of up to 100 disc like structures called thylakoid, this is where the first stage of photosynthesis takes place.
What is the stroma?
the matrix of the chloroplast where the second stage of photosynthesis takes place.
What are the features of the chloroplast that benefit their function?
the grana gives a large surface area for the first stage of photosynthesis; stroma has the enzymes for the second stage of photosynthesis; chloroplasts have ribosomes and DNA to quickly manufacture proteins for photosynthesis.
What are the two types of endoplasmic reticulum?
the rough endoplasmic reticulum, has ribosomes on the surface; and the smooth endoplasmic reticulum, has no ribosomes.
Describe the structure of the endoplasmic reticulum.
a complex network of flattened, membrane-bounded sacs called cisternae. Often has ribosomes on the cytoplasmic side.
What is the function of the endoplasmic reticulum?
forms a system of channels for transporting materials through the cytoplasm. one type has ribosomes on its surface and is the site of protein synthesis. the other type has no ribosomes and is where steroids and other lipids are synthesised.
Why might a cell have a more extensive ER?
cells that manufacture and store a large quantities of carbohydrates, proteins and lipids.
Describe the structure of the Golgi apparatus.
a stack of membrane-bounded flattened sacs in the cytoplasm.
What is the function of the Golgi apparatus?
Receives proteins synthesised on the ER and prepares them for the secretion from the cell. this often involves adding carbohydrate to the proteins to make them into glycoproteins.
What is the function of lysosomes?
They are responsible for destroying worn-out organelles and digesting the contents of vacuoles formed by phagocytosis.
Describe the structure of a lysosomes.
a vesicle containing digestive enzymes.
What types of cells are lysosomes most commonly found in?
secretory cells such as phagocytes and epithelial cells.
Describe the structure of ribosomes.
A very small organelle not bounded by a membrane. consists of a large and a small subunit. made of protein and RNA.
What is the function of ribosomes?
Uses the information in nucleic acid to synthesise proteins.
What is the structure of the cell wall?
It consists of cellulose microfibrils and other polysaccharides.
What is the function of the cell wall?
provides mechanical support and protection. Prevents cell from bursting.
What is the structure of the plasma membrane?
a phospholipid bilayer with intrinsic and extrinsic protein molecules.
What is the function of the plasma membrane?
its a partially permeable barrier which controls the passage of substance into and out of the cell.
Describe the structure of a vacuole.
a sac bounded by a single membrane. contains cell sap which is a solution of mineral salts, pigments, organic acids and other substances
What is the function of a vacuole?
They store waste product and other substances. Changes in volume affect the turgidity of the cell.
Describe the structure of the centrioles.
A pair of short cylinders. each made up of nine fibres
What is the function of the centrioles?
form a spindle-shaped structure of protein fibres on which the chromosomes move during nuclear division.
What is the purpose of cell specialisation?
so the cells can perform particular role they specialise to suit the role it carries out.
How do cells become specialised?
The genes within a cell can be expressed. each type of specialised cell has different cells switched on to produce different organells, the rest of the genes are switched off.
What are tissues?
A collection of similar cells that perform a specific function.
Give some examples of tissues.
epithelial, line the surfaces of organs with protective or secretory functions; xylem, transports water and mineral ions through a plant.
What are organs?
organs are a combination of tissues coordinated to perform a variety of functions.
What are Organ systems?
systems of organs grouped together to perform a particular function.
What are the two main types if cells?
Prokaryotic cells and eukaryotic cells
Where is DNA found in prokaryotic cells?
no true nucleus, so DNA is free floating and circular. Can have plasmids.
Where is DNA found Eukaryotic cells?
In the nucleus, with a nuclear envelope, has no plasmids and is linear
Which Type of DNA is associated with proteins?
Eukaryotic DNA is associated with histones.
Which type of cell has membrane bound organells?
Eukaryotic cells
Which type of cell does not have chloroplasts?
Prokaryotic cells, just bacterial chloroplasts in the cell surface membrane.
Which type of cell can have a capsule?
Prokaryotic cells can have an outer mucilaginous layer.
What is a prokaryotic cell wall?
a physical barrier made of murein that protects the cell from damage.
What is different about the ribosomes in a prokaryotic cell over those in a eukaryotic cell?
The ribosomes are smaller in prokaryotic cells.
What is the purpose of the prokaryotic cell wall?
it protects from other bacteria and allows cells to clump together.
What are prokaryotic pili?
short hair like structures used for bacterial reproduction.
What is a plasmid?
a small circular DNA that helps survival in adverse conditions, carry antibiotic resistance.
What are the flagellum?
tails used by bacteria for locomotion.
What are viruses?
Acellular, non-living particles.
What does a virus need to multiply?
a host cell, to use it’s organelles to produce it’s proteins.
Describe the structure of a virus.
it has genetic material and reverse transcriptase enzyme within a protein coat called a capsid, with attachment proteins. They can have a lipid envelope.
What are the two ways of cell division?
mitosis and meiosis
What is mitosis?
Cell division that produces two genetically identical daughter cells for the repair of tissues and growth.
What is meiosis?
cell division that produces four genetically different daughter cells with half the number of chromosomes, to produce gametes for sexual reproduction.
What is the period of the cell cycle where the cell is not dividing?
interphase.
What happens during interphase?
The DNA replicates and the cell grows larger, copying the organells.
What are the Four stages of the cell cycle?
Prophase, metaphase, anaphase and telophase (PMAT)
What happens during Prophase?
The chromosomes condense and centrioles start moving to opposite ends and nuclear envelope breaks down.
What happens during Metaphase?
The chromosomes line up along the equator of the cell and become attached to the spindle by the centromere.
What happens during Anaphase?
The chromosomes divide, separating the pairs of sister chromosomes, and the spindles contract, pulling chromatids to opposite ends of the cell , centromere first.
What happens during telophase?
The chromatids reach the opposite poles on the spindle and uncoil to become long and thin again. a nuclear envelope forms.
What is the last stage of the cell cycle?
Cytokinesis, when the cytoplasm divides , the cell pinches in the middle leading to cleavage. there are now two daughter cells.
Describe the structure of chromosomes.
Two sister chromatids joined in the middle by a bundle of protein called a centromere.
How do prokaryotic cells divide?
through binary fission
Describe the process or binary fission.
The circular DNA replicates and attach to the cell membrane, then the cell pinches in the middle with cell membrane forming between the two molecules.
How do viruses replicate?
They attach to host cells using attachment proteins, then ingect the host with enzymes and nucleic acid. which implants DNA into the host cell’s DNA, using the host cell for metabolic processes.
What are the three stages of the cell cycle?
Interphase, nuclear division and division of cytoplasm.
How long does it take for a typical mammalian cell to go through the cell cycle?
24 hours
What is the longest stage in the cell cycle?
interphase, takes up to 90% of the time in the cell cycle
How is the cell cycle regulated?
The replicated DNA is checked at multiple checkpoints by proteins called cyclin-dependent kinases (CDKs).
What are the three phases of interphase?
Growth phase, organelles replicate and cell grows; Synthesis phase, DNA is replicated; Growth phase 2, cell gets even bigger, DNA checked for errors.
What is Cancer?
a group of diseases caused by a growth disorder in cells caused by cell cycle being unregulated.
How does a tumour become cancerous?
if it changes from benign to malignant
What is a tumour?
a group of abnormal cells that forms when cells grow and divide more than they should.
What is the difference between a benign and malignant tumour?
malignant tumour grow rapidly and are less compact; benign tumours grow slowly and are more compact.
How is cancer commonly treated?
blocks part of the cell cycle, killing dividing cells and ceasing cancer growth.
How do chemotherapy drugs block the cell cycle?
They prevent DNA replication and spindle formation
What are the downsides of chemotherapy drugs?
They can target rapidly dividing healthy cells such as blood, skin and hair cells.
