Cell Biology Flashcards
Electron microscope
The use electrons to create a magnified image of the sample.
The specimen also has to de dead as the sample is put into a vacuum to be magnified.
have higher resolving power. This means that we can study cells in much finer detail. This has enabled biologists to see and understand many more sub celular structures.
Describe the principle on the limitation of using a transmission electron microscope to investigate cell stricture
Principles: electrons pass through/enter thin specimen. Denser parts absorb more electrons. So denser parts seem darker. Electrons have a short wavelength so give a higher resolution.
Limitations: cannot look at living material must be in a vacuum. Specimen must be very thin. Artefacts present. Complex staining method long prep time. Image not in 3D only 2D images are produced.
Artefacts
• An artefact is things that aren’t meant to be in the microscope sample that are not part of the specimen.
• Examples of artefacts include dust, air pockets and/or halos. Artefacts are usually created when preparing the specimen.
• Artefacts are common in electron microscopes due to the difficulty and the time it takes to set up which creates lots of opportunities to mess up.
Magnification and scale
long wavelength means that light microscopes can only distinguish between objects if they are 0.2 micrometers or further apart.
This limitation can be overcome by using beams of electrons rather than beams of light.
With their shorter wavelength, beams of electrons can distinguish between 2 objects as close as 0.1 nanometers.
scanning electron microscopes (SEM)
In scanning electron microscopes (SEM) electrons are scattered by surface contour of the specimen producing a 3D image.
Density in images - more electrons attract and absorbed because the subject is more dense meaning it is darker. This is the same in light microscopes as well.
DNA in eukaryotes
the DNA is contained in nucleus. Their DNA is tightly wrapped around proteins called histones.
Together the DNA and histone proteins form chromosomes.
Their DNA is a linear molecule, meaning the ends are not joined together to form a loop.
What are the main 3 uses of protein
• Enzymes for chemical reactions
• Structural proteins eg organelle movement.
• Transport molecules eg haemoglobin.
Synthesising proteins
The instructions for encoding the amino acid sequence of a protein are in the gene of that protein, these are part of the chromosomes in the nucleus.
the genetic info coded by that gene is converted to mRNA (transcription) this mRNA leaves the nucleus to carry out translation
Some proteins are secreted from cells. They are translated on a ribosome attached to the rough endoplasmic. The proteins make their way through the ER and the Golgi apparatus.
What is the nucleoplasm
The nucleus contains a material called the nucleoplasm. The nucleoplasm contains molecules such as nucleotides and enzymes.
What is the nuclear envelope
there is a double membrane called the nuclear envelope. The nuclear envelope consists of two phospholipid bilayers. There are also nuclear pores, which allow molecules to enter and leave the nucleus.
The outer membrane with the nuclear envelope is continuous with the rough endoplasmic reticulum, which plays a role in protein synthesis.
What is chromatin
Nucleus also contains chromatin, which consists of DNA coiled around proteins called histones, the DNA and histone proteins form chromosomes. Chromosomes are not visible in the nucleus unless the cell is undergoing mitosis or meiosis.
What is the nuclelolus.
Inside the nucleus on an electron micrograph, the region that is darker than the rest is called the nuclelolus.
This is where a special type of rRNA. Ribosomal RNA forms the structure of ribosomes. The nucleolus is also where the ribosome subunits are assembled.
What happens when a polypeptide chain passes into the lumen of the rough er
This is where the chain folds into its tertiary structure. Now, it makes its way through the rough ER. During the process, the polypeptide can be modified.
The polypeptide is packaged into vesicles and transported into the golgi apparatus
Endocytosis and exocytosis
Endocytosis - entering the lumen of the rough ER
Exocytosis - exiting the lumen of the rough ER
Structure and function of the endoplasmic reticulum
Rough and smooth ER both have folded membranes called cisternae
Rough have lots of ribosomes on the cisternae.
RER function- protein synthesis
SER - synthesis and store lipids and carbohydrates
What is the function of the golgi apparatus
Add carbohydrates to proteins to form glycoproteins
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
Form lysosomes
• Molecules are ‘labelled’ with their destination
• Finished products are transported to cell surface in Golgi vesicles where they fuse with the membrane and the contents in released.
What happens when the protein passes through the golgi
Once the protein has travelled through the golgi apparatus, it is packaged into vesicles. These vesicles can then fuse with the cell membrane and the protein can be secreted from the cell. Or the protein can form part of the cell membrane or go on to form lysosomes.
Functiom of lysosome
- hydrolyse phagocytic cells
• Completely break down dead cells (autolysis)
• Exocytosis - release enzymes to outside of cell to destroy material
• Digest worn out organelles for reuse of materials
What are mitochondria key for
Key for aerobic respiration to produce the energy carrying molecule ATP. In respiration, the energy contained in the chemical bonds of glucose, is transferred to ATP.
Two stages of repsiration
- Glycolysis - takes place in cytoplasm
- The Krebs Cycle and oxidative phosphorylation (requires oxygen) - in the mitochondria
Matrix
Within the mitochondria there is a fluid called the matrix.
The enzymes for the kreb cycle are found in the matrix (liquid inside mitochondria).
What is a chloroplast surrounded by
Chloroplasts are surrounded by a double membrane.
What are thylakoids
The membrane bound flattened disks are called thylakoids, this is where the light dependant reactions take place so contain chlorophyll and enzymes.
What are stacked thylakoids called
These discs stacked are called granum, by stacking them, light can be absorbed more efficiently. When the discs are stacked, they are connected by a flattened membrane called lamelllae.
Liquid in chlorplasts
Chloroplasts contain a liquid called stroma, this is where the light independent reactions take place so contains enzymes.
What else is in chloroplats
Starch granules are also contained in the chloroplasts as a product of photosynthesis.
Chloroplasts contain a loop of DNA which contains genes which encode for some proteins. And they also contain ribosomes to synthesise protei
Reactions in chloroplast
The energy trapped in photosynthesis is contained within the chemical bonds in the glucose molecule.
The light dependant reactions use chlorophyll to harvest light energy. The energy is then transferred to the other molecules.
Light independent reactions take place in both light and dark conditions.
Comparing prokarys to eukarys
- Prokaryotic cells are much smaller than eukaryotic cells
- No membrane bound organelles, DNA is found in cytoplasm so DNA is in a circular chromosome with no free ends.
- The DNA in prokaryotes is not bound to histone proteins and no nucleus
- Cell wall made of mureinics.
Cell walls in rpokaryot
Prokaryotic cells are surrounded by a cell wall, in bacteria this is called peptidoglycan which is also called murein. This is a polymer formed between peptides and polysaccharide molecules.the cell wall helps maintain the structure of the cell.
What is the flagellum
Flagellum - helps the cell move. The prokaryotic flagellum has a different structure to the ones found in eukaryotes.
What is pili
Some bacteria also have fine protein strands on their surface called pili. This helps bacteria attatched to surfaces and other bacteria.
What is a mesosome
Mesosomes - infoldings in the cell membrane of prokaryotic cells. An example of an artefact when bacterial cells are prepared for electon microscopy
What is the nutrient stores for bacterial cell
Bacteria also contain lipid droplets and glycogen granules. Whcih act as nutrient stores for the bacteria cell.
What is the cell wall made of
Made of polysaccharide cellulose which is a polymer betaglucose.cellulose molecules can form hydrogen bonds forming larger structures called microfibrils which is extremely strong. Provides strength to the cell. Controls osmosis to prevent bursting.
Also contains murein and glycoprotein
What is between cell walls
a layer called the middle lamella, which is a layer of polysaccharides aswell as calcium and magnesium ions. The function of this is to act as a glue between plant cells.
Cell walls in prokaryotic cells compared to eukaryotic cells.
Prokaryotic - cell
Contains murein, a glycoprotein
Eukaryotic
In plant and fungi cells
Plants- made of microfibrils of the cellulose polymer.
Fungi - made of chitin, a nitrogen-containing polysaccharide
Genetic material in viruses
All viruses contain genetic material (DNA or RNA). The genetic material is contained inside a protein structure called a capsid. On the surface there are attachment proteins, these allow the virus particle to attach and enter the host cell.
How do viruses reproduce
Many viruses are broadly spherical. Viruses cannot reproduce independently, can only reproduce inside of a host cell where it can use the host cells enzymes to copy itself. Viruses are acellular meaning not based on cells. They are not counted as living organisms.
What is the plant cell vacuole surrounded by
A plant cell vacuole is surrounded by a membrane called the tonoplast. This controls which chemicals enter and leave the vacuole.
Cell sap
The fluid in the vacuole is called the cell sap. Cell sap contains disolved sugars, mineral salts and amino acids.
The cell sap has low water potential, this means water moves into the plant by osmosis and that water enters the vacuole. This creates a hydrostatic pressure acting outwards. Causing cytoplasm to press against the cellulose cell wall.
Vesicles and large vacuoles
Vesicles - sacs of fluid enclosed by a membrane.
Larger and longer living vesicles are called vacuoles so can transport/carry other molecules.
They also are key in the removal of waste materials.
Animal cell vacuoles are temporary structures, however in plant cells there is a larger permanent vacuole.
Plasma membranes
cells and organelle membranes have the same structure.
The membranes are described as a fluid-mosaic model due to the mixture and movement of the phospholipids, proteins, glycoproteins and glycolipids it is made of.
All of the these molecules arranged within the phospholipid bilayer create the partially permeable membrane, that is the cell-surface membrane.
Several functions of the plasma membranes
- Keeping all cellular components inside the cell
- Allowing selected molecules in and out of the cell
- Isolating the organelles from the rest of the cytoplasm allowing cellular processes to occur separately
- Allows cell to change shape eg red blood cells
Phospholipids in plasma membranes
The phospholipids align as a bilayer due to the hydrophilic heads being attracted to water and the hydrophobic tails being repelled by water.
What are glycoproteins
• Chains of carbohydrates attached to proteins.
• They are the receptors (carbohydrate components extend outside the cell)
Functions of gylcoprotein:
Functions:
Recognition sites for hormones and neurotransmitters
Allows cells to recognise each other (ie lymphocites can recognise body’s own cells)
Helps cells attach to each other to form tissues
Cholestrol as a component of the plasma membrane
Cholestrol is present in some membranes too and this will restrict the lateral movement of other molecules in the membrane. This is useful as it makes the membrane less fluid at high temperatures and prevents water and dissolved ions leaking out of the cell.
Cholestrol
• Cholesterol molecules provide strength to membranes
• They are very hydrophobic, they prevent water loss and loss of ions from the cell
• They limit the movement of phospholipids by attracting the tails, this allows them to have some flexibility.
Functions of cholestrol:
Reduce the fluidity at high temperatures and too rigid under cool conditions
Supposed to stop lateral movement.
Increases the strength of the cell surface membrane
Fluid mosaic model name
“Fluid” used because phospholipid molecules can move around each other meaning membrane is flexible and can change shape. “Mosaic because the membrane is studded with protein molecules and the arrangement of these proteins vary.
Functions of membranes in cells
- Act as barriers eg between internal contents of cell and the external environments.
- Membranes separate parts of organelles
- Membranes can also be a location for chemical reactions
- Membranes are involved in cell signalling.
Hydrophobic center in membranes
The hydrophobic center prevents water-soluble molecules from easily passing through. This is because hydrophilic substances are polar (have a charge), these substances cannot easily pass through the non-polar region of the membrane.
Water molecules can pass through because they are extremely small.
The cell-surface membrane is based on the phospholipid bilayer. The cell surface membrane contains a large number of protein molecules.
Intrinsic protein
- protein that spans the whole length of the bilayer. It contains a channel/carrier in the center of the protein where molecules can pass through the gap, it is lined with hydrophilic amino acids and is filled with water molecules. Carrier proteins are another example that can change their shape or position to transfer from one side of the membrane to the other. They have hydrophobic amino acids on the outside surface of the protein. These can interact with the hydrophobic tails in the bilayer
Partially Intrinsic protein -
Only spans through half of the bilayer. As it cant pass through the bilayer it cannot be used for transport.
Partially Intrinsic protein -
Only spans through half of the bilayer. As it cant pass through the bilayer it cannot be used for transport.
Glycolipids
Glycolipids - carbohydrates that are found attached to phospholipid molecules. Often used when cells come into contact with each other. The glycolipids on the surface of one cell can be recognised by another cell. Can also act as antigens for example determining blood group.
Key facts about an optical light microscope
• A beam of light is condensed to create the image.
• Poorer resolution due to light having a longer wavelength.
• Lower magnification
• Colour images
• Can view living samples
Electron microscope key facts
• A beam of electrons is condensed to create the image.
Electromagnets are used to condense the beam.
• Higher resolving power as electrons have a short wavelength.
• Higher magnification
• Black and white images
• Sample must be in a vacuum. and therefore non-living
Disadvantage and advantage of optical light microscope
Light microscopes have a poor resolution due to the long wavelength of the light.
Small organelles in a cell or not visible but living samples can be examined and a colour image is obtained
How do Transmission electron microscopes work
Extremely thin specimens are stained and placed in a vacuum. An electron gun produces a beam of electrons that pass through the specimen. Some parts absorb the electrons and appear dark. The image produced is 2D and shows detailed images on the internal structure of cells.
How do scanning electron microscopes work
The specimens do not need to be thin, as the electrons are not transmitting
through. Instead, the electrons are beamed onto the surface and the electrons are scattered in different ways depending on the contours. This produces a 3D image.
What is the eyepiece graticule
can be used to measure the size of objects you are viewing under the microscope. However, each time you change the objective lens, and therefore the magnification, you have to calibrate the eyepiece to work out what the distance is between each division represents at that magnification.
How to set up calibration
Step I - Line up the stage micrometer and eyepiece graticule whilst looking through the eye piece
Step 2 - Count how many divisions on the eyepiece graticule fit into one division on the micrometer scale.
Step 3 - Each division on the micrometer is 10um, so this can be used to calculate what one division on the eye piece graticule is at that current magnification
Proteins as components of plasma membrabne
The peripheral proteins provide mechanical support, or they are connected to proteins or lipids to make glycoproteins and glycolipids. The function of these is cell recognition, as receptors.
The integral proteins are protein carriers or channel proteins involved in the transport of molecule across the
Protein channels form tubes that fill with water to enable water-soluble ions to diffuse, whereas the carrier proteins will bind with other ones and larger molecules, such as glucose and amino acids, and change shape to transport them to the other side of the membrane.
Structures in the nucleus
Nuclear envelope
Nuclear pores
Nucleoplasm
Chromosomes
Nucleolus
Function of nucleus
Site of dna replication and transcription
Contains the genetic code for each cell
What is the structure of thr golgi
Folded membranes making cisternae
Secretary vesicles pinch off from the cisternae
Structure of lysosomes
Bags of digestive enzymes which can contain up to 50 diff enzymes
Structure of membranes
Double membrane
Inner membrane called the cristae
Fluid centre called the mitochondrial matrix
Loop of mitochondria DNA
Function of mitochondria
Site of aerobic respiration
Site of ATP production
• DNA to code for enzymes needed in respiration
Structure of ribosomes
Small made up of two sub-units of protein and rRNA
80s- large ribosome found it eukaryotic cells (25nm)
70S - smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts.
Function of ribosomes
Site of protein synthesis
Structure of chloroplasts
Surrounded by a double membrane
Contains thylakoids (folded membranes embedded with pigment)
Fluid filled stroma contains enzymes for photosynthesis
Found in plants
Function of chloroplasts
Photosynthesis
Structure and function of vacuole
Filled with fluid surrounded by a single membrane called tonoplast
Function - make cells turgid and therefore provide support
Temporary some store of sugars and amino acids
pollinators.
Structure and function of cell wall
In plant and fungi cells
Plants- made of microfibrils of the cellulose polymer.
Fungi - made of chitin, a nitrogen-containing polysaccharide
Funcgiomn - provide structual strength to the cell
Structure and function of the plasma membrane
Found in all cells
Phospholipid bilayer - molecules embed within and attached on the outside (proteins, carbohydrates, cholesterol)
Function
Controls the entrance and exit of molecules
Ribosomes in prokaryotic cells compared to eukaryotic
Pro - 70S - smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts.
Eukaryotic
80s- large ribosome found it eukaryotic cells (25nm)
Plasma membrane being partially impermeable
Molecules that pass through the plasma membrane:
Lipid soluble substances (e.g. some hormones) and very small molecules (e.g. CO,, O,, H,O)
Molecules that cannot pass through the membrane:
Water soluble (polar) substances ( Sodium ions) and large molecules (glucose)
