Cell Structure Flashcards
What is an object?
What is magnification?
It is the material that is put under a microscope.
The magnification of an object is how many times bigger the image is when compared to the object.
What is the formula for finding magnification?
image/actual size
What is the resolution of a microscope?
It is the minimum distance apart that two objects can be in order for them to appear as separate items.
What is a tissue placed in before cell fractionation?
Explain why these conditions are used?
It is placed in a cold, buffered isotonic solution.
cold - to reduce enzyme activity that might break down the organelles.
isotonic (same water potential) - to prevent organelles bursting or shrinking as a result of osmotic gain or loss of water.
buffered - so that the pH does not fluctuate (any change in pH could alter the structure of the organelles or affect the functioning of enzymes.
What happens in homogenation?
Cells broken up by homogeniser - releases organelles from the cell - homogenate (resultant fluid) is filtered to remove any complete cells and large pieces of debris
What happens during ultracentrifugation? (for animal cells)
tube of filtrate placed in centrifuge and spun at low speed
heaviest organelles (nuclei), are forced to bottom to form the sediment
Fluid at top (supernatent) removed, leaving just the sediment of nuclei
supernatent is transferred to another tube and spun in the centrifuge at a faster speed than before
next heaviest organelle (mitochondria) are forced to bottom of tube
process continues , whereby at each increased speed, the next heaviest organelle is sedimented and separated
What are the two main advantages of electron microscopes?
electron beam has a very short wavelength and microscope can therefore resolve objects well - has a high resolving power
as electrons are negatively charged the beam can be focused using electromagnets
What can we say about the best modern electron microscopes in terms of specs? What are some requirements of electron microscopes?
can resolve objects that are just 0.1 nm apart - 2000 better than a light microscope
because electrons are absorbed/deflected by the molecules in the air, a near-vacuum must be created withing the chamber of an electron microscope for it to work effectively.
What are the two types of electron microscopes?
transmission electron microscope -TEM
scanning electron microscope - SEM
How does the TEM work?
consists of an electron gun that produces a beam of electrons that is focused onto the specimen by a condenser electromagnet.
How are observations established in the TEM?
The beam passes through a thin section of the specimen. Parts of the specimen absorb electrons and therefore appear dark. Other parts of the specimen allow the electron to pass through and so appear bright.
an image is produced on a screen and this can be photographed to give a photomicrograph.
Why cannot a TEM always achieve a 0.1 nm resolving power in practice?
There are difficulties preparing the specimen that limit the resolution that can be achieved
a higher energy electron beam is required and this may destroy the specimen
What are the main limitations of the TEM?
whole system must be in a vacuum so living specimens cannot be observed
a complex ‘staining’ process is required and even then the image is not in colour
the specimen must be extremely thin
image may contain artefacts
result is a flat 2-D image, and can be overcome by a slow, complicated process by taking a series of sections through a specimen to then build a 3-D image.
How does a SEM work? How is it similar to a TEM and how is it different?
SEM directs a beam of electrons on to the surface of the specimen form above, rather than penetrating it from below. Beam is then passed back and forth across a portion of the specimen in a regular pattern - electrons scattered by specimen and and this pattern depends on the contours of the specimen surface - a 3D image can be built up.
SEM has same limitations as TEM but specimens do not need to be extremely thin and electrons do not penetrate.
Basic SEM has a lower resolving power than a TEM, around 20 nm, but is still ten times better than a light microscope
What are the 9 most important organelles in eukaryotic cells?
Nucleus Mitochondrion Chloroplasts Endoplasmic reticulum Golgi apparatus Lysosomes Ribosomes Cell wall Vacuoles
What are the 5 parts of the nucleus and what is the function of the nucleus?
Nuclear envelope, nuclear pores, nucleoplasm, chromosomes, nucleolus
It is the control centre of the cell, produces mRNA and tRNA, manufactures ribosomes, retains genetic information.
What are the 3 parts of the mitochondrion and what is the function of the mitochondrion?
Double membrane (controls entry and exit), cristae, matrix The site of aerobic stages of respiration (Krebs cylce and oxidative phosphorylation). Responsible for production of ATP
What are the 5 parts of the chloroplasts and what is the function of the chloroplasts?
Chloroplast envelope, grana, made up of thylakoids and within, have chlorophyll, stroma
They harvest sunlight and carry out photosynthesis.
What are the 2 types of endoplasmic reticulum and what are the functions of both?
Rough endoplasmic reticulum (RER) - has ribosomes present on outside.
provide large SA for glyco/protein synthesis + provides pathway for transport of materials, esp. proteins, through cell.
Smooth endoplasmic reticulum (SEM) - no ribosomes on surface, more tubular
synthesise, store and transport lipids and carbohydrates
What does a golgi apparatus look like and what are the functions?
similar to SER but more compact, consists of stacks of membranes that make up flattened sacs (cisternae)
- add carbohydrates to proteins to form glycoproteins
- produce secretory enzymes
- secrete carbohydrates
- transport, modify and store lipids
- form lysosomes
How are lysosomes produced and what are their functions?
Formed when the vesiceles produced by the Golgi apparatus contain enzymes such as proteases and lipases.
- hydrolyse material ingested by phagocytic cells
- release enzymes to the outside of the cell (exocytosis)
- digest worn out organelles to ensure useful chemicals can be reused
- completely break down cells after death (autolysis)
What are the features of ribosomes and what is the function of them?
Occur in the cytoplasm or RER, 80S-in eukaryotic, 70S-in prokaryotic cells, mitochondria + choroplasts
Two subunits- one large and one small
Site of protein synthesis
What are the two features of cell walls and what are their functions?
- consist of a number of polysaccharides, such as cellulose (made of cellulose microfibrils)
- thin layer called middle lamella that marks the boundary between adjacent cell walls and cememnta adjacent cells together
functions: -provides mechanical strength to prevent bursting through osmosis - mechanical strength to plant as a whole
- to allow water to pass along it- to contribute to the movement of water through the plant.
What are the cell walls of algae and fungi made up of?
Algae - either cellulose or glycoproteins, or both
Fungi - no cellulose, but a mixture of chitin, glycan and glycoproteins
What are the features of vacuoles and what are their functions?
single membrane around it is called the tonoplast
- contains a solution of mineral salts, sugars, amino acids, wastes and pigments.
functions: - support cells by making them turgid - sugars and amino acids may act as temporary food source
- pigments may colour petals to attract pollinating insects
What is the order of cell specialisation?
tissues (e.g. epithelial, xylem) -organs (e.g. stomach, leaf) - organ systems
What are the three organ systems in humans?
digestive system
respiratory system
circulatory system
What are the structures in a bacterial cell?
cell wall, capsule of slime (bacteria), cell-surface membrane, circular strand of DNA, plasmids
What are the structures of viruses?
nucleid acids, (within) capsids (viruses), attachment proteins
What are the 6 structures of HIV?
genetic material (RNA) reverse transcriptase (enzyme) attachment protein capsid lipid envelope matrix
What happens in prophase?
DNA supercoils
Nuclear envelope disintegrates
(in animals) centrioles divide and move to poles
spindle fibres form
What happens in metaphase?
centromeres attach to spindle fibres
chromosomes line up at equator
What happens in anaphase?
centromeres split
chromatids move to separate poles
What happens in telophase?
chromosomes become lengthened
spindle fibres disintegrate
nucleus starts to reform
What happens in cytokinesis?
the cytoplasm divides
How does cell division occur in prokaryotic cells?
through binary fission
circular DNA replicates + both copies attach to cell membrane
plasmids replicate
cell membrane begins to grow between the two DNA molecules and begins to pinch inwards, dividing the cytoplasm into two
new cell wall forms between the two molecules of DNA - two identical daughter cells produced
How do viruses replicate?
Attach to host cells with the attachment proteins on their surface.
inject their nucleic acid into host cell.
viral components start to be produced.
assembled into new viruses
What are the three stages of the cell cycle?
interphase - occupies most of cell cycle
nuclear division - nucleus divides in two (mitosis) or four (meiosis)
cytokinesis - cytoplasm divides to produce two or four (mitosis or meiosis)
How does chemotherapy work?
prevents DNA from replicating
inhibits metaphase stage of mitosis by interfering with spindle formation
Problems of chemotherapy?
they also disrupt the cell cycle of normal cells that divide rapidly such as hair-producing cells
