Cells (3-3.8) Cell Structure Flashcards
What are microscopes?
They are instruments that produce a magnified image of an object.
What is magnification?
How many times bigger the image is when compared to the object.
What is the magnification formula?
Magnification= size of image divided by size of real object
What is resolution?
The minimum distance apart that two objects can be in order to to them to appear as separate items
What is cell fractionation?
The process where cells are broken up and the different organelles they contain are separated out
What happens before cell fractionation?
The tissue is placed into a cold buffered solution of the same water potential as the tissue
What are the two stages of cell fractionation?
Homogenation and Ultracentrifugation
What is homogenation?
When cells are broken up by a homogeniser (blender) to release organelles from the cell. The homogenate is the filtered to remove debris and any complete cells
What is ultracentrifugation?
The process by which the fragments in the filtered homogenate are separate in a machine (centrifuge)
For animal cells, describe the ultracentrifugation in the steps
1) tube of filtrate is placed in the centrifuge, spun at low speed
2) heavy organelles (nuceli) forced to bottom of tube, where they form a thin sediment
3) fluid at top (supernatant) is removed, leaving just the sediment (nuclei)
4) supernatant is transferred to another tube and spun in the centrifuge at a faster speed than before.
5) next heaviest (mitochondria) are forced to bottom of tube
6) at each increased speed, the next heaviest organelle is sediment Ed and separated out
Why do light microscopes have poor resolution?
They have a relatively long wavelength of light
What are the two main advantages of an electron microscope?
1) Electron beam has a very short wavelength - can resolve objects well (high resolving power)
2) electrons are negatively charged - the beam can be focused using electromagnets
What needs to be created in order for an electron microscope to work effectively?
A near-vaccum has to be created within the chamber of an electron microscope
What are the two types of microscopes?
1) Transmission Electron Microscope (TEM)
2) Scanning Electron Microscope (SEM)
What does a TEM consist of?
An electron gun that produces a beam of electrons that’s is focuses onto the specimen by a condenser electromagnet.
What is the resolving power of a TEM?
0.1 nm
What are the main limitations of a TEM?
1) Whole system must be in a vaccum, therefore living specimens cannot be observed.
2) a complex ‘staining’ process is required and even then the image is not in colour
3) specimen must be extremely thin
4) image may contain artefacts
How does the SEM work?
SEM directs a beam of electrons on to the surface of the specimen from above. Beams then passed back and forth across a portion of the specimen in a regular pattern. Electrons are scattered by the specimen and the pattern of this scattering depends if contours if the specimen surface.
Does the SEM have a lower resolving power than TEM?
Yes, around 20nm
What is an eyepiece graticule?
It is a glass disc that is placed in the eyepiece of a microscope
What is etched on the glass disc?
A scale
How long is the scale and in how many sub divisions?
10mm long and in 100-sub divisions
What must be done first with the graticule before being used?
It has to be calibrated for a particular objective lens
What microscope do you need to calibrate an eyepiece graticule?
A stage micrometer
What is the scale on a stage micrometer?
2mm long and has 0.1nm (10micrometers)
How do you workout the graticule?
Mm divided by graticule x100
How do you calculate linear magnifications of drawings and photographs?
1) Measure length X-Y
2) convert measurement in drawing to microns (x1000)
3) new measurement divided by line representing in the cell = magnification
What is magnification formula?
Actual size divided by the size of the image
What is cell ultrastructure?
The internal structure of a cell that suits for it’s own function
What are the main things in eukaryotic cells?
They have:
A distinct nucleus
Membrane bound organelles
What are the eukaryotic organisms?
They are:
Animals
Plants
Algae
Fungi
What is the nucleus function?
Control centre producing mRNA and tRNA which allows for protein synthesis inside the cell (assembles ribosomes)
What does the nucleus contain (5 structures)?
Nucleoplasm
Chromatin
Nuclear pores
Nucleolus
Nuclear envelope
What is the function of the nucleoplasm?
It’s a jelly like substance making up the bulk of the nucleus
What is the function of Chromatin?
Protein bound linear piece of DNA
What is the function of the nuclear envelope?
It’s controls the entry and exit of substances in and out the nucleus
What is the function of the nuclear pores?
Allows for the passage of large molecules out of the nucleus
What is the function of the Nucleolus?
It is a spherical region that synthesise rRNA and assembles ribosomes
What is the function of the mitochondria?
It is the site of aerobic respiration
What are the 4 structures found in a mitochondria?
Matrix (ribosomes and DNA)
Cristae
Outer membrane
Inner membrane
What is the role of an outer membrane for a mitochondria?
It controls entry and exit of molecules
What is the role of the inner membrane for a mitochondria?
It contains Cristae (infolding of membrane) that have enzymes attached to carry out respiration.
What is the role of the matrix in a mitochondria?
It allows for the production of their own proteins and contains enzymes involved in respiration
What is the function of the endoplasmic reticulum?
It’s a series of sheet like membranes that produces proteins to allow the rest of the cell to function
What are the two types of endoplasmic reticulum?
Rough and smooth
What does RER have on the outer surfaces of the membrane?
Ribosomes
What is the function of RER?
Large surface area for synthesis of proteins and gylcoproteins.
Provides a pathway for the transport of substances like proteins through the cell
What is the function of SER?
Synthesise, store and transport both lipids and carbohydrates.
What is the function of the golgi apparatus?
modify, sort, and package macromolecules that are synthesized by the cell
What is the golgi apparatus made out of?
Cisternae and vesicles
What are cisternae?
Flattened sacs
What are vesicles?
Membrane sacs
What are the functions of the golgi apparatus?
Modification of proteins
Add carbohydrates to some
proteins
Label proteins to be stored and sent to correct places
Transported to vesicles to edge of the cell and then releasee
Produce secretory ezymes
Secretes carbohydrates
Modify, transport and store lipids
Form lysosomes
What is the function of lysosomes?
break down and recycle cellular waste and unwanted material.
What does lysosomes breakdown?
Ingested material
What do lysosomes hydrolyse?
Cell walls of bacteria (white blood cells)
What do lysosomes release to the outside of the cell and what is the process called and what does it do?
Enzymes, and the process is exocytosis and this means that it destroys material around the cell
What does autolysis mean?
Complete break down of cells after that have died
What is the function of ribosomes?
The site of protein synthesis
What are the two types of ribosomes?
80s and 70s
Where are 80s ribosomes found? And how big are they?
Found in eukaryotic cells, is around 25nm in diameter
Where are 70s ribosomes found? And what organelles are slightly smaller than 80s ribosomes?
Found in prokaryotic cells, mitochondria and chloroplasts, is slightly smaller
What whare the two sub units of ribosomes?
Small and large
What does each subunit contain in a ribosome?
rRNA and protein
What is the function of the cell wall?
Contribute to the overall strength of the cell wall and prevent the cell from bursting under the pressure created by osmotic entry of water. But also contributes to the movement of water through the plant.
What does the cell wall consist of?
Microfibrils of the polysaccharide cellulose, embedded in a matrix, a thin layer (middle lamella)
What are the cell walls of Algae made of?
Cellulose or gylcoproteins or a mixture of both
What are the cell walls of fungi not contain, but do contain instead?
Do not contain cellulose, but contains chitin (nitrogen containing polysaccharide), gylcan and glycoproteins.
What is the function of chloroplasts?
Carry out photosynthesis
What are the structures of chloroplasts?
Chloroplast envelope, the grana (stacks of thylakoid), chlorophyll, the stroma, grana membranes, DNA, ribosomes
What is the stroma?
A fluid filled matrix (synthesis of sugars) take place. Light in dependant reaction
What is within the stroma?
Starch grains
What does the grana membranes provide for the attachment of chlorophyll, electron carriers and ezymes that carry out the first stage of photosynthesis?
A large surface area
What does the fluid of the stroma possess needed to make sugars in the 2nd stage of photosynthesis?
ezymes
Why do chloroplasts contain DNA and Ribosomes?
So they can quickly and easily crate some of the proteins needed for photosynthesis
What is the function of a vacuole?
Supports herbaceous plants and parts of them by making the cells turgid, sugars and amino acids acts as temporary food store, pigments may colour pettles so they can also attract pollinating insects
What is a vacuole?
A fluid filled sac bounded by a single membrane.
What is the single membrane around the vacuole?
Tanoplast
What is cell specialisation?
When a cell becomes specialised to perform a specific function.
In an embryo, what is common with all the cells
They are all identical
What are all cells in a human created by?
Mitotic divisions from the fertilised egg
How then does the cell become specialised?
Some genes are switched on (expressed) and some switched off in any one cell, at any one time.
The shape of the cells vary but what else?
The number of each organelle
What are tissues?
Collection of cells that work together to perform a specific function
Where are epithelial tissues found?
Animals and consist of sheets of cells
Where is the xylem found?
Plants and is made of number of similar cell types
What is an organ?
Collection of tissues that work together to perform a specific function
Why are capillaries not organs, big veins and arteries are?
Capillaries have just one tissue
What is an organ system?
Collection of organs that work together to perform a specific function
What doe the digestive system do?
Digests and processes food
What does the respiratory system do?
Used for breathing and gas exchange
What does the circulatory system do?
Pumps and circulates blood
What are the common structures of a prokaryotic cell?
Cell surface membrane, ribosomes, food stored as gylcogen granules and lipid droplets, DNA is circular and is not associated with proteins, cytoplasm, Cell wall
What are the three structures that are not all found in prokaryotic cells?
Plasmid, capsule and flagellum
What is a plasmid?
Small circular piece of DNA
What is a capsule?
Mucilaginous layer of slime
What is a flagellum?
Its a similar like tail used for locomotion
In bacteria, what is the cell wall made up of?
Murein (peptidoglycan) - polymer of polysaccharide and peptide
What is the role of the cell surface membrane?
Acts as a differentially permeable layer, controlling the entry and exit of chemicals
What is the role of the capsule?
Protects bacterium from other cells and helps groups of bacteria to stick together for further protection
Viruses are acellular, what does this mean?
Viruses are not cells
Are viruses living or non living? And why?
Non living because they do not reproduce by themselves (with a host only) and cannot process metabolic reactions to allow reproduction.
What does viruses contain that can reproduce only in a host?
Nucleic acids
What is a capsid?
A nucleic acid which is enclosed within a protein coat
Mitosis produces two ________ ____ that have the same number of _______________ as the parent cell and each other.
daughter cells, chromosomes
Meiosis produces _ daughter cells, each with ____ the number of chromosomes of the parent cell
4, half
What is mitosis?
a division of a cell that results in each of the daughter cells having an exact copy of the DNA as the parent cell.
Mitosis is always preceded by a period during which the cell is not dividing, what is this process called?
Interphase
What is interphase?
A period of considerable cellular activity that includes a very important event, the replication of DNA.
Two copies of DNA after DNA replication remain where in a cell?
the centromere
What happens in prophase?
1) Chromosomes become visible
2) Chromosomes shorten and thicken
3) Centrioles move to opposite poles of the cell
4) Spindle fibres form from the centrioles
5) nuclear envelope breaks down
6) nucleolus disappears
What happens in Metaphase?
1) Chromosomes come across to be made up of 2 chromatids
2) chromatids are joined by the centromere
3) spindle fibres attach to the chromosomes attach to the centromere
4) the chromosomes are pulled to the equator by the spindle fibres to which they are attached to
What happens in Anaphase?
1) centromere divides into 2
2) spindle fibres pull the individual chromatids of each chromosome towards opposite poles
3) now can be referred as chromosomes
What happens in telophase ?
1) chromosomes reach their respective poles and become longer and thinner, finally disappearing all together.
2) left widely spread chromatin
3) spindle fibres disintegrate and the nuclear envelope and nucleolus re-forms.
what happens in cytokinesis?
the cytoplasm divides into 2, a separation in 2 daughter cells.
Cell division in prokaryotic cells takes place by a process called?
Binary Fission
What happens in binary fission? (4 simple steps)
1) Circular DNA molecule replicate and both copies attach to the cell membrane
2) plasmids replicate
3) cell membrane grows between 2 DNA molecules, pinching inwards, dividing of cytoplasm into 2
4) cell wall forms between 2 DNA molecules, original cell into 2 daughter cells , each with copy of circular DNA and variable number of plasmids.
How do viruses replicate?
1) attaching to the host cell with attachment proteins on their cell surface membrane
2) injects its nucleic acid into cytoplasm of host cell
3) produces viral components inside cell
4) assembles new viruses
What are the 3 importance for mitosis?
Growth, repair and reproduction.
In the Cell Cycle there are 3 stages what are they in order?
1) interphase
2) nuclear division (mitosis or meiosis)
3) cytokinesis)
What is the length of a complete cell cycle in a mammalian cell? What % is interphase?
24 hours, 90% interphase
The rate of mitosis can be affected by what?
1) the environment of the cell and by growth factors
2) two types of gene - mutations
in the treatment of cancer, how can we block a part of the cell cycle to kill dividing abnormal cells?
1) preventing DNA from replicating
2) inhibiting he metaphase stage of mitosis by interfering with spindle formation
Use of drugs can disrupt the cell cycle of healthy cells, why is this bad?
Hair producing cells divide rapidly and are vulnerable to damage
Drugs are useful for killing abnormal cells. True or False
True
