B2 - Basic Components Of Living Organisms Flashcards
Nucleus (structure)
Double nuclear envelope, nuclear pores, nucleolus, chromatin
Double nuclear envelope
A double membrane which compartmentalises the nucleus and prevents damage. Protects the DNA.
Nuclear pores
allows molecules to enter )e.g nucleotides for DNA replication) and leave the cell e.g mRNA leaves the cell.
Nucleolus
Site of ribosome production. Composed of RNA and proteins.
Chromatin
Is the DNA (with associated histone proteins). Contains the genetic code which controls the activity of the cell
Cytoskeleton (functions)
Whole cell, support stability, scaffolding. Maintains the shape of the cell. Allows movement of cilia / flagella. Changing shape of cell / cytokinesis / pseudopodia / phagocytosis / endocytosis / exocytosis / muscle contraction. Organelles can be moved or held in place. Movement of chromosomes / chromatids / mRNA. Movement of vesicles along microtubules.
Cytoskeleton (components)
Microfilaments, microtubules, intermediate fibres
Microfilaments
Fibres made from the protein actin. They are responsible for movement of the cell and cytoplasm during cytokineses.
Microtubules
Formed by the globular protein tubular. They polymerise to form tubes that determine the shape of the cell. They also act as tracks for organelles moving around the cell.
Intermediate fibres
Gives strength to cells and helps maintain integrity.
Rough endoplasmic reticulum (structure)
Stacks of membrane bound (fluid filled) sacs which form sheets called cisternae. Attached to the nucleus and covered with ribosomes. Consists of an interconnected system of flattened sacs.
Rough endoplasmic reticulum (function)
Site of protein synthesis.
Smooth endoplasmic reticulum (structure)
Similar to the RER but lacks ribosomes - is a system of interconnected tubules.
Smooth endoplasmic reticulum (function)
Responsible for lipid, carbohydrate, and steroid synthesis, and storage.
Ribosomes (structure)
A 2 subunit organelle. Made from RNA and protein. Not membrane bound. Very small organelles: about 22nm in diameter. Found free floating in the cytoplasm or attached to the rough ER.
Ribosomes (function)
These are where protein is made. They assemble amino acids into proteins in chains using mRNA
Mitochondria (structure)
Oval shaped. Surrounded by two membranes (double membrane). The inner membrane forms finger-like structure called Cristal which increases the surface area. The solution inside is called a matrix which contains enzymes for respiration. Mitochondrial DNA - small amounts of DNA, enable mitochondrion to reproduce and create enzymes.
Mitochondria (function)
Site of aerobic respiration. As a result of respiration, they release ATP (energy carrier in cells).
Golgi apparatus/body (structure)
Stacks of flattened, membrane bound sacs (cisternae). These are continuously formed from the ER at one end and budding off as Golgi vesicles at the other.
Golgi apparatus/body (function)
Allows internal transport. Receives proteins from the RER. Modifies and processes molecules (such as new lipids and proteins) and packages them into vesicles. These may be secretory vesicles (if the proteins need to leave the cell) or lysosomes (which stay in the cell). Makes lysosomes. Lipid synthesis.
Lysosomes (structure)
They are spherical sacs surrounded by a single membrane.
Lysosomes (function)
They contain powerful hydrolysis digestive enzymes known as lysozymes. Their role is to break down worn out components of the cell or digest invading cells.
Centrioles (structure)
A component of the cytoskeleton, composed of many micro tubules. Small hollow cylinders that occur in pairs next to the nucleus in animal cells only. Each centriole contains a ring of 9 triplet microtubules.
Centrioles (function)
Makes a copy of itself during cell division and then helps to form the spindle in cell division
Cilia (structure)
Hair like extensions that protrude from some animal cell types. In cross section they have an outer membrane and a ring of nine pairs of protein microtubules inside with two microtubules in the middle. Known as 9 + 2 arrangement. Arrangement allows movement
Cilia (function)
Sensory function (e.g nose), beat creating a current to move / waft / fluid / mucus / objects. For locomotion.
Plasma membrane (structure)
The membrane found on the surface of animal cells and in side the cell wall of plant and prokaryotic cells. Phospholipid belayer. Composed of proteins and lipids
Plasma membrane (function)
Regulates the movement of substances into and out of the cell. Contains reception molecules which allow it to respond to chemical like hormones.
Flagella (structure)
Similar to cilia but longer. They protrude from cell surface and are surrounded by the plasma membrane. Like cilia they have a 9 + 2 arrangement.
Flagella (function)
(Whip-like) enables a cells mobility. The microtubules contract to make the flagellum move. Propel cells forward e.g sperm cells.
Chloroplast (structure)
Double membrane which encloses the stroma. Stroma contains: starch grains, lipid stores, DNA, RNA, ribosomes. Series of membrane-bound flattened sacs called thylakoids in the stroma. Thylakoids stacked together are called grana. Grana are linked together by lamella. The grana contains chlorophyll.
Chloroplast (function)
Photosynthetic reactions
Cell wall (structure)
Made of b-glucose microfibrils - complex carbohydrate. Cell wall is fully permeable to substances. Thin layer called the middle lamella which marks the boundary between adjacent cell walls and ‘cements’ adjacent cells together.
Cell wall (function)
Gives the plant mechanical strength. Gives the plant cell support and its shape. Contents of plant cell can ‘push’ against the cell wall (turgid cell). This gives the cell (and the whole plant) good support
Light microscope (overview)
Use light to form an image
Optical microscopes have a maximum resolution of around 0.2 micrometers or 200 nano meters
Microscopes can be used to observe eukaryotic cells, nuclei and maybe mitochondria and chloroplasts.
Light microscope (advantages)
Inexpensive to buy and operate
Small and portable
Simple sample preparation
Specimens can be living or dead
Light microscope (disadvantages)
Limited resolution of optical microscopes.
Using light, it is difficult to resolve two objects that are closer than the wavelength of around 500-650nm
They cannot be used to observe ribosomes, ER or lysosomes
Maximum magnification is typically x1500
Scanning electron microscope (SEM) (overview)
SEM’s scan a beam of electrons across the surface of the specimen
This bounces pff the surface and the electrons are detected, forming an image.
SEM’s therefore form 3D images that show the surface of a specimen
Magnification x500,000 or less
SEM (advantages)
Can be used on thick or 3D specimens
Allow external 3D structure to be observed.
SEM (disadvantages)
Lower resolution than TEM’s
Cannot be used on live specimens
Does not produce a colour image
Transmission electron microscope (overview)
TEM’s use electron magnets to focus a beam of electrons, which is transmitted through the specimen.
Denser parts of the specimen absorb more electrons, making them appear darker on the final image
TEM (advantages)
High resolution images = more detail
Internal structures can be seen
Magnification x1,000,000 or more
TEM (disadvantages)
Only used with very thin specimens or thin sections of an object.
Cannot be used to observe live specimens because of the vacuum inside the TEM plus all the water removed
Lengthy treatment required to prepare specimens. Artefacts could be introduced these look like real structures but are staining.
Colour image and 2D
Light scanning confocal (overview)
Light microscope has also improved and these microscopes are a relatively new technology
Cells viewed are stained with fluorescent dyes
A thick section of tissue or small living organism are scanned with a laser beam.
The laser beam is reflected by the fluorescent dye.
Multiple depths of the tissue section are scanned to produce an image. As if the laser beam is building the image layer by layer.
Laser scanning confocal (advantages)
Used on thick or 3D specimens
External 3D structure is observed
Very clear, high resolution because the laser beam, can be focused at a very specific depth. Cytoskeleton can be observed
Laser scanning confocal (disadvantages)
Slow process and takes a long time to obtain an image
Laser could cause photo damage to the cells.
Interrelationships protein production
• DNA in the nucleus contains the code/gene to make protein.
• The particular gene (e.g. insulin) is copied by mRNA, which takes the copy of the gene out of
the nucleus via the nuclear pore to the ribosome (on the rough ER).
• The protein is synthesized on the ribosome (bound to rough endoplasmic reticulum).
• The protein then passes into the cisternae of the rough ER and it is packaged into a vesicle.
• The vesicle moves to the golgi apparatus (via the microtubules of the cytoskeleton), and fuses with the golgi apparatus.
• The protein enters the golgi apparatus.
• The golgi apparatus processes and structurally modifies the protein e.g. adds a carbohydrate
chain.
• Golgi repackages the protein into a secretory vesicle.
• Secretory vesicles travel along the microtubules and fuses with the cell surface membrane.
• Contents of the vesicle (i.e. the protein) is released by exocytosis.
Differences between prokaryotic and eukaryotic cells (size)
Prokaryotic are much smaller (less the 2 micrometers) whereas eukaryotic are much larger (about 10-100 micrometers)
Differences between prokaryotic and eukaryotic ( nucleus)
Prokaryotic has no nucleus, the DNA is free in the cytoplasm and the DNA is circular. The DNA is not associated with proteins and some DNA is in the form of plasmids.
Eukaryotic DNA is present in the nucleus. The DNA is linear (many chromosomes). It is associated with proteins called histones and has no plasmids.
Differences between prokaryotic and eukaryotic cells ( organelles )
Prokaryotic cells have few organelles and no membrane-bound organelles, e.g mitochondria
Eukaryotic cells have many organelles (mitochondria and other membrane-bound organelles present)
Differences between prokaryotic and eukaryotic (ribosomes
In prokaryotic cells the ribosomes are about 20nm
In eukaryotic cells are about 25-20nm
Differences between prokaryotic and eukaryotic (cell wall)
In a prokaryote the Cell wall is made of a polysaccharides, but not cellulose or chitin
In a eukaryote there is no cell wall in animals, cellulose cell wall in plants or chitin cell wall in fungi
Differences between prokaryotes and eukaryotes (capsule)
In a prokaryotic cell it is the Protective slimy layer which helps the cell to retain moisture and adhere to surfaces.
Eukaryotic cells do not have a capsule
Differences of prokaryotes and eukaryotes (types of cell division)
In prokaryotes they use binary fission
In eukaryotes they use mitosis or meiosis
Prokaryotic and eukaryotic differences (overall)
Prokaryotic cells:
Do not have a nucleus
Do not have membrane-bound organelles
And include all bacteria cells
Eukaryotic cells:
Do have a nucleus
Do have membrane bound organelles
Includes all animal and plant cells
Plasmids
Prokaryotic cells may also contain extra small rings of DNA called plasmids. Plasmids code for very specific features such as antibiotic resistance
Plasmids can be shared between bacteria to pass on resistance and also resistance can be passed on through binary fission.
Structures always present in prokaryotic cells
Plasma membrane
Circular DNA (sometimes referred to as a chromosome)
Cytoplasm
Ribosome
Cell wall made of cross-linked peptidoglycan
Structures sometimes present in a prokaryotic cell
Pili
Plasmid
Capsule
Mesosome
In folding of plasma membrane
Flagellum
Pili
For attachment to other cells or surfaces, involved in sexual reporoduction
Plasmid
Small circle of DNA several may be present
Capsule
Protective slimy layer which helps the cell to retain moisture and adhere to surfaces. Also gives additional protection.
Mesosome
In folding of plasma membrane, associated with DNA during cell division, and helps with formation of new cell walls
Infolding of plasma membrane
May form a photosynthetic membrane, or carry pout nitrogen filtration.
Flagellum
For locomotion, verity simple structure
Microscopy calculations
image size = actual size x magnification
Why use staining important in light microscopy
Because it increases contrast and makes certain transparent organelles visible.
