2.1 - Eukaryotic cells Flashcards
magnification definition
a measure of how much bigger the image we see is than the real object
resolution definition
a measure of how close together 2 objects can be before we see them as 1
magnification and resolution of an optical/light microscope
magnification - x1500
resolution - 200nm
how does an optical microscope work
a beam of light goes through the specimen from underneath.
the objective lens magnifies the image.
the eyepiece lens focuses the image onto the eye.
the specimen can be living or dead, and staining can be used to identify particular cells or subcellular structures.
produces a 2-D image.
Advantages and disadvantages of optical microscopes
Advantages:
1 - can see living and dead specimens
2 - relatively cheap
3 - relatively light and portable
4 - produce coloured images
Disadvantages:
1 - preservation and staining may alter the image of the specimen
2 - lower magnification and resolution than electron microscopes
how do electron microscopes work
a beam of electrons is scattered by the specimen.
electromagnetic or electrostatic lenses focus the electron beam to form an image.
the specimen must be in a vacuum, so it is dead.
what is a transmission electron micrograph (TEM)
a micrograph produced by an electron microscope that gives a 2-D image, but high magnification than SEMs - up to x500,000
what is a scanning electron micrograph (SEM)
a micrograph produced by an electron microscope which produces a 3-D image, but has a lower magnification than TEMs
advantages and disadvantages of electron microscopes
Advantages:
1 - very high magnification and resolution
Disadvantages:
1 - specimen must be in a vacuum, so dead
2 - preparing specimens is highly skilled work, and they undergo lots of treatment so there is likely to be artefacts which can alter the image
3 - very expensive
4 - very large
5 - have to be maintained at a constant temperature and pressure in order to maintain the internal vacuum
produce black and white images
what’s the difference between staining used in electron microscopes and optical microscopes
electron microscopes - staining is used to improve the scattering of electrons and create sharp contrasts in the image
optical microscopes - staining is used to highlight specific cells or subcellular structures
describe the stain haematoxylin
stains nuclei of plant or animal cells purple, blue or brown
describe the stain methylene blue
stains the nuclei of animal cells blue
describe the stain acetocarmine
stains the chromosomes in dividing nuclei in plant and animal cells
describe the stain iodine
stains starch-containing material in plant and animal cells
magnification and resolution of a scanning electron microscope
magnification - x500,000
resolution - 3-10nm
magnification and resolution of a transmission electron microscope
magnification - x500,000
resolution - 0.5nm
what are membranes mostly made up of
lipids and proteins
describe a phospholipid
-2 fatty acids – glycerol – phosphate group
-the fatty acids are hydrophobic (don’t mix with water
-the phosphate group is hydrophilic (can interact with water) and is charged so is polar
describe the simple phospholipid bilayer
-the hydrophilic heads point into the water while the hydrophobic tails stay protected in the middle
-this structure is a unit membrane
-only fat-soluble organic molecules can pass through the simple phospholipid bilayer, so we need integral and peripheral proteins, pores, gated channels glycolipids and glycoproteins
describe the integral membrane proteins in the phospholipid bilayer
-integral proteins span from one side of the layer to the other
-they can form pores, which are permanently open to let substances through, because they have hydrophilic amino acids
-or can form gated channels, channels which can be open or closed depending on conditions within the cell
what is the main function of membrane proteins
to help substances move across the cell membrane
what are the 2 types of membrane proteins (based on location)
integral - span from one side of the membrane to the other
peripheral - lie on the surface of the membrane
describe the peripheral membrane proteins in the phospholipid bilayer
-some peripheral proteins can be for structure
-or act as enzymes
-or receptors for hormones and other molecules
describe glycoproteins in the phospholipid bilayer
glycoproteins - proteins with a carbohydrate molecule attached
-allows certain cells to attach to eachother forming tissue like nervous tissue
-present antigens to T cells
-receptors for hormones
describe glycolipids in the phospholipid bilayer
glycoproteins - carbohydrates attached to phospholipid molecules
-the glycolipids on the surface of one cell can be recognised by the glycolipids on another cell, which determines whether the cells will interact.
what is the protoplasm
cytoplasm, organelles and nucleus together
can the nucleus and organelles be seen with a light or electron microscope
nucleus and mitochondria - light
other organelles (ultrastrucutre) - electron
describe the structure and function of the nuclear envelope
nuclear envelope - a double membrane
-there’s the inner membrane and outer membrane, both are phospholipid bilayers
-2 membranes are needed to protect the fragile DNA from enzymes and chemicals in the rest of the cell
-the nuclear envelope has nuclear pores allowing mRNA and ribosomes to travel through the nucleus
-it contains 2 main substances: nucleic acids (ribonucleic acid and deoxyribonucleic acid) and proteins
describe the structure and function of the nucleolus
nucleolus - a dense area of almost just DNA and protein
-where ribosomes are made
what is the structure of the mitochondria
-outer mitochondrial membrane.
-inner mitochondrial membrane, where there are enzymes for oxidative phosphorylation
-both the outer and inner mitochondrial membrane contain their own DNA
-the inner mitochondrial membrane is highly folded creating cristae, creating a large surface area, increasing the rate of the enzymes.
-the fluid matrix contain enzymes for Krebs cycle.
-also contains mitochondrial DNA, containing genes for some of the enzymes involved in aerobic respiration.
-mitochondrial ribosomes synthesise proteins coded by the mitochondrial DNA
what is the endosymbiotic theory of the evolution of eukaryotic cells
-the idea that mitochondria and chloroplasts existed as their own their own cells not existing inside eukaryotic cells
-this is backed by the evidence that mitochondria have their own DNA
-and that the 70s ribosomes in mitochondia and chloroplast reproduce independently when a cell divides
where are centrioles found and what do they do
-in each cell there is a pair of centrioles (a centrosome), usually found near the nucleus
-each centriole is made up of 9 tubules
-during cell division the centrioles pull apart into spindle fibres, involved in the movement of chromosomes.
what 2 materials does the cytoskeleton contain
-the cytoskeleton fills the cytoplasm
-it contains microfilaments and microtubules
what are microfilaments, what is their function
-protein fibres
-involved in cell movement e.g. when white blood cells move from the blood into infected tissue
-involved in cytokinesis when the cytoplasm pinches
what are microtubules, what is their role
-tiny tubulin (a type of protein) tubes
-centrioles are types of microtubules, which form spindle fibres during cell division
-involved in the movement of organelles
-help to determine the shape of cells
are vacuoles found in animal cells
vacuoles can be present but they are not permanent
they are created and lost as needed
e.g. white blood cells form vacuoles around pathogens
what are contractile vacuoles
-occur in simple animals living in fresh water
-contractile vacuoles allow water content to be controlled
where are centrioles not found
in flowering plants
Prokaryotes
what are 2 key features of eukaryotes
-they have a membrane-bound nucleus
-they have membrane-bound organelles
what are chromatin
-when the cell is not actively dividing, DNA is bonded to proteins called histones, making chromatin
-histones wrap around DNA to make it more compact, because DNA is a very large molecule
what are the structures within the nucleus
nuclear envelope
nucleoplasm
nucleolus
chromatin
nuclear pores
what is the function of mitochondria
during cellular respiration molecules are oxidised, producing ATP
what are ribosomes made from
ribosomal RNA and proteins
what does the “s” is 80s and 70s ribosomes stand for, and what does it tell us about the ribosomes
-“s” stands for svedberg, a unit to measure how quickly particles settle in a centrifuge
-the rate of sedimentation tells us about the shape and size of the particle
-80s ribosomes settle quicker than 70s ribosomes because they are heavier
what are 80s ribosomes made up of
-a 40s small subunit
-a 60s large subunit
-a 1:1 ratio of RNA:protein
what are 70s ribosomes made of
-a 30s small subunit
-a 50s large subunit
-a 2:1 ration of RNA:protein
where are 70s ribosomes found
mitochondria, chloroplast, and prokaryotes
what is the function of the rough endoplasmic rectilium
-sheets of folded membranes form flattened sacs called cisternae
-cisternae covered in 80s ribosomes
-during translation, mRNA threads through the 80s ribosomes and passes into the lumen of the RER
-here the protein folds into it’s tertiary structure and is modified (e.g. glycoproteins are made)
-the RER then packages the polypeptides into vesicles and transports them to the golgi apparatus
-large surface area for the synthesis, storage and transportation of proteins
give an example of exocytosis in the rough endoplasmic rectilium
-some proteins like digestive enzymes and hormones are not used inside the cell
-once the RER isolates these proteins it needs to transport them out of the cell without interfering with the cell’s activities
what is the function of the smooth endoplasmic rectilium
-doesn’t have ribosomes
-synthesise and transport carbohydrates, steroids and lipids
-these proteins are sent to the Golgi apparatus where they are modified and transported
what is the function of the Golgi apparatus
-has cisternae
-vesicles containing proteins pinch off the ER adn fuse with the Golgi apparatus
-here they are modified further
-the protein will reach its final structure in the Golgi apparatus - its now a functional protein
-the Golgi apparatus packages the proteins into vesicles
-they exit and fuse with the cell membrane so they can be secreted from the cell, or form part of the cell membrane, or form lysosomes
if a cell secretes a lot of protein what does this indicate about its organelles
it has a lot of rough endoplasmic rectilium
what are the functions of lysosomes
-vesicles containing digestive enzymes
-break down food into simple chemicals
-break down organelles
-some fuse with the outer cell membrane to release its enzymes outside of the cell
-take part in apoptosis
what is apoptosis and what happens
-apoptosis is programmed cell death
-needed when an entire cell is wearing out, the cell needs to be removed during development or the cell has mutations
-the cell’s lysosomes rupture, releasing their digestive enzymes which destroys the whole cell
what is the function of the cells wall
gives plant cells turgidity and structure
needed to withstand the hydrostatic pressure exerted onto the cell wall
is the cell wall permeable
-the cell wall is made of mostly cellulose
-making it freely permeable to any substance dissolved in water.
-but the cell wall can be impregnated with suberin in cork tissues
-or lignin to produce wood
-suberin and lignin decrease the cell wall’s permeability greatly
describe the process of the cell wall forming when a plant cell divides into 2 new cells
-the middle lamella forms, it’s made of pectin which acts like a glue holding neighbouring cell walls together.
-cellulose microfibrils and matrix build up on either side of the middle lamella.
-this forms the primary cell wall, where cellulose microfibrils are orientated in the same direction so the cell wall is weak and flexible.
-the secondary cell wall forms where cellulose microfibrils are laid densely at different angles, making the cell wall rigid
-lignin or pectin can be added to make the cell wall more rigid or make it impermeable to water
what is the symplast
-a strand of cytoplasm which runs from one plant cell into the neighbouring plant cell through the plasmodesma (a hole in the cell walls)
what is a plasmodesma
-a cytoplasmic bridge between 2 plant cells
-substances and communication can be passed between the cells through the plasmodesmata
-plasmodesmata are formed when cells divide, these cells do not separate completely as some cytoplasm remains between them (symplast)
what surrounds a vacuole in a plant cell
what is the vacuole filled with
the tonoplast
cell sap (a solution of various substances dissolved in water)
what is the function of the tonoplast
-a membrane that surrounds the plant cell vacuole
-controls the movements of substances into and out of the vacuole, therefore controls water potential of the cell
what is the function of the cell sap
-the cell sap causes water to move into the cell by osmosis, therefore the cytoplasm is kept pressed against the cell wall, keeping the cell turgid
what are the overall functions of a vacuole
-maintaining the shape and structure of the cell
-store pigments
-vacuoles in seed and fruit cells store proteins
-store waste products
do all plant cells contain chloroplast
-not all plant cells contain chloroplast
e.g. cells in flowers, roots, seeds or transport tissue
-only cells from the green parts of the plant
-however most plant cells contain the genetic information needed to make chloroplasts so sometimes different areas of the plant turn green and start photosynthesising
what are the similarities between mitochondria and chloroplasts
-contain their own DNA
-are surrounded by an outer membrane
-have a very large folded inner membrane, creating a large surface area where enzyme-controlled reactions can take place
-endosymbiotic theory of evolution of prokaryotic cells: both are thought to have existed outside the cell as their own prokaryotic organisms, then were engulfed and became part of other cells
what are amyloplasts and their function
-amyloplasts are organelles developed from leucoplasts (main function: storage)
-store starch, which can be converted into glucose and used to provide energy when needed
-found in large numbers
-colourless
-only are present in plant cells (but not all plant cells)
what is the definition of tissue
a group of specialised cells carrying out a function in the body
these specialised cells are similar and have developed from the same type of cell
what is the definition of organ
a structure made up of several different types of tissues grouped together to carry out a particular function in the body
what are the 4 main tissue types
epithelial tissue
muscle tissue
connective tissue
nervous tissue
briefly describe the common structure of all epithelial tissues
cells in epithelial tissue are tightly packed and form a smooth surface that protects cells and tissues below
they all have an extracellular basement membrane
what is the definition of organ system
many organs work together to carry out a large scale function in the body
What are the structures within chloroplast
Chloroplast envelope - inner and outer membrane
70s ribosomes
Starch grains
Thykolaid
Stroma
Grana
A loop of DNA
Describe thykoloid/grana in chloroplasts
-thykoloid and grana make up a membrane system where the light-dependent stage of photosynthesis occurs
-thykoloids are fluid filled flattened sacs
-thykoloids can be stacked to form grana (or 1 granum)
What is the function of stroma in chloroplast
-stroma is a fluid which fills chloroplast
-the site of the light-independent stage of photosynthesis
What is the function of the loop of DNA in chloroplasts
-the loop of DNA codes for some proteins within the chloroplast, the rest of the proteins are coded by the plant cell’s DNA
-the proteins coded by the loops of DNA are synthesised in the 70s ribosomes
What is the function of the starch grains within chloroplast
-the starch grains store the glucose produced by photosynthesis
What is the function of the starch grains within chloroplast
-the starch grains store the glucose produced by photosynthesis
how do you measure the size of a specimen under a microscope
by using an eyepiece graticule and stage micrometer
