2A Flashcards
Labelled Animal Cell diagram
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Labelled Plant cell diagram
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what’s the difference between Algal Cells and Plant cells
They both carry out photosynthesis, however they can be unicellular and multicellular. they contain the same organelles, however the chloroplasts in many algal cells are different shapes and sizes to plant chloroplasts.
what’s the difference between Fungal Cells and Plant cells
Fungal cells can also be multicellular or unicellular, and they are very similar to plant cells, except their cell walls are made of CHITIN, not cellulose. Also, they don’t have chloroplasts as they don’t photosynthesise
Cell surface membrane Organelle
Regulates movement of substances into and out of the cell. It has receptor molecules on it, which allow responses to chemicals, like hormones
Nucleus Organelle
Contains Chromosomes, and controls the cells activities (Transcription) DNA also contains instructions for making proteins. The nuclear pores allow substances (mRNA) to move out of the nucleus and into the cytoplasm.
Nucleolus Organelle
Makes Ribosomes
Mitochondrion Organelle
Have a double membrane, the inner forms a structure called Cristae. Inside is the matrix where enzymes are involved in respiration. It is the site of aerobic respiration, to produce ATP - a common energy source in the cell.
Chloroplast Organelle (Draw if can)
A small, flattened structure found in plant and Algal cells. They obtain Thylakoids, stacked into grand, connected by lamella. This is where photosynthesis takes place.
Goligi Apparatus Organelle
A group of fluid-filled membrane bound flattened sacs. Vesicles are often seen at the edges of these sacs. It processes/Modifies (by adding carbohydrates to form glycoprotein/glycolipids) and packages new lipids and proteins. It also makes Lysosomes
Golgi Vesicle Organelle
A small, fluid filled sac in the cytoplasm, surrounded by a membrane and produced by the Golgi apparatus. It stores lipids and proteins made by the Golgi apparatus and transports them out of the cell
Lysosome Organelle
A round Organelle surrounded by a membrane with no clear internal structure. it contains digestive enzymes (Lysozyme’s) which are used to digest invading cells or to break down worn out components of the cell
Ribosomes
A very small Organelle that floats free in the cytoplasm or its attached to the RER. it is made up of proteins and RNA. It is the site of protein synthesis
Rough Endoplasmic Reticulum (RER) Organelle
A system of membranes closing fluid-filled space, covered in ribosomes. It folds and processes proteins that have been made by Ribosomes
Smooth Endoplasmic Reticulum (SER) Organelle
Similar to RER but with no ribosomes, it synthesises and processes lipids.
Cell wall
A rigid structure that surrounds cells in plants, algae and fungi. It supports the cells and prevents them from changing shape.
Cell Vacuole Organelle
A membrane-bound Organelle found in the cytoplasm. it contains cell sap - a weak solution of sugar and salts. the surrounding membrane is called the TONOPLAST. It helps maintain pressure inside the cell and keeps them rigid, it stops them filtering and isolates unwanted chemicals inside the cell.
Cell organisation
- Cells group together to form a tissue.
- A group os tissues work together to form organs.
- Organs work together to form an organ system
What are Prokaryotes?
Single-celled organisms, which are smaller than eukaryotic cells, with no membrane bound organelles, like a nucleus, in their cytoplasm.
Prokaryotic Cell Replication - Binary Fission
- The Circular DNA and plasmids replicate - circular DNA replicates once, but plasmids can be replicated many times
- The cell gets bigger and the DNA loops move to opposite ‘poles’
- The cytoplasm begins to split and a new cell wall begins to form
- The cytoplasm divides and two daughter cells are produced.
What are viruses?
Viruses are ‘acellular’ - they’re not cells. They are just nucleic acids surrounded by protein. They invade and reproduce inside host cells of other organisms.
Virus Structure
There is no Cell-surface membrane, no cytoplasm, and no ribosomes. They have a protein coat, called a capsid, with attachment proteins sticking out from them to help viruses cling to host cells. They are much smaller than bacteria cells. Some, For Example HIV, have lipid envelopes
Virus Replication
Because they’re not alive, they don’t undergo cell division. Instead, they cling onto a host cell by their attachment proteins and inject their DNA or RNA into the host cell. They then uses the cells ‘machinery’ to replicate the virus. Some cells replicate the virus particles so much they burst
What is Magnification?
How much bigger the image is than the specimen
How is Magnification calculated (The formula)
Mag = Size of Image / Size of real Object
IMO (top, left, right)
Converting units
mm to micro (x1000)
micro to mm (/ 1000)
micro to nm (x1000)
nm to micro (/1000)
What is Resolution?
How detailed the image is - how well the microscope can distinguish between two points that are close together. if the microscope cannot distinguish between the objects, increasing the magnification won’t help
Types of Microscopes
Optical (Light) Scanning Electron (SEM) Transmission Election (TEM)
Optical microscopes
Use light to form an image. Max. Resolution of about 0.2 micrometers. Therefore organelles such as Ribosomes, Lysosomes snd ER can’t be seen. Mitochondria can be seen however not in perfect detail. The Maximum magnification is x1500
Electron Microscopes
Use Electrons to form an image. Higher resolution (around 0.0002 micrometers) than Optical microscopes, so more detailed image seen. Maximum magnification is x 1500000. They are black and white images, but coloured by a computer
Transmission Electron Microscope (TEM)
Focus a beam of electrons through a specimen. Denser parts absorb more e- so they appear darker on the image. They Give high resolution, but the specimen must be dead, very thin, stained and in a vacuum with no artefacts to disrupt the image - a complex staining and preparation process.
Scanning Electron Microscope (SER)
Scan a beam of electrons across the specimen. This knocks off electrons from the specimen, which are gathered by a Cathode rat tube to form an image. By the e- bouncing off, a 3D image is produced. They give lower resolution images than TEM’s; however they can be used on thick specimens, but, the specimens need to be dead
Plasma Membranes
All membranes around and within cells have the same basic structure, known as plasma membranes. The cell surface membrane is the plasma membrane which surrounds the cell. The Membranes are composed of phospholipids, proteins and carbohydrates, arranged in a fluid mosaic structure.
Phospholipid Bilayer
Phospholipid molecules form a bilayer that gives the membrane its basic structure, with its hydrophobic tails and hydrophilic heads that prevent the passage of ions and water-soluble molecules, allow lipid-soluble substances to enter and leave the cell as well as making the membrane more flexible
Proteins in the plasma membrane
They are embedded randomly in the phospholipid bilayer, with Extrinsic and Intrinsic proteins.
- Extrinsic- on the surface or only partly embedded, that give mechanical support and when in conjunction with carbohydrates, they act as receptors to molecules such as hormones
- Intrinsic - span the bilayer, some acting as carriers/channels to transport water-soluble material, whilst some allow active transport of ions across the membrane. Others are enzymes
Carbohydrates in the plasma membrane
They are attached to lipids and proteins on the outside of the membrane forming glycolipids and Glycoproteins, which are important for cell recognition
Fluid Mosaic Model described
- Fluid because the individual phospholipids can move in relation to one another, being flexible, allowing changes in shape and can be self sealing.
- Mosaic because the proteins are embedded the same way tiles are in a mosaic.
Specialised cells
A cells structure helps carry out its function, for example:
- Root Hair Cell - absorbing water and mineral ions, so they have an increase surface area for uptake, many mitochondria to provide ATP for Active Transport and have thin cell walls for a short diffusion distance
- Palisade cells needed for photosynthesis have large numbers of chloroplasts and are long and thin to absorb more sunlight
Prokaryotic structure
They have cell walls (protection and maintaining shape, made from murein - a glycoprotein)
- Cell surface membrane (controls entry and exit of substances)
- Smaller ribosomes (70s)
- No nucleus, just circular DNA (Not associated with proteins) which floats freely in the cytoplasm, as well as plasmids, small loops of DNA that aren’t part of the main circular DNA, which contain genes for things like antibiotic resistance, that can be passed down generations.
- Some have flagellum (for movement)
- Slime capsules (for protection against attaching cells) They aerobically respire in a region of the cell surface membrane, as they don’t have mitochondria
Preparing Microscope Slides for Optical Microscopes
- Pipette a small drop of water onto the centre of the slide. - Use tweezers to place a thin section of the specimen on top of the water droplet.
- Add a drop of dye to stain the specimen to highlight objects in a cell
- Finally add the cover slip by carefully tilting and lowering it so it covers the specimen - try not to get any air bubbles in as they will obstruct the view of the specimen.
What are Microscope Artefacts
Artefacts are things that can be seen down the microscope that aren’t part of the specimen you’re wanting to look at (Dust, air bubbles, fingerprints etc.) Artefacts are usually made during the preparation of the specimen and are common in Electron micrographs because there is a lot of preparation needed.
What are the steps in Cell fractionation?
Homogenisation, Filtration and Ultracentrifugation
Cell Fractionation - Homogenisation
Plasma membranes of cells are broken down to release organelles. This can be done by a microblender - which forces the cell surface membrane open, or by grinding up the cells.
This should be down in COLD, ISOTONIC BUFFER SOLUTION!
- Cold to inactivate the enzymes
- Isotonic so the water potential is maintained so the organelles don’t burst/shrivel up through osmosis
- Buffer to keep the pH constant so enzymes and proteins are not damaged (Tertiary Structure not altered)
Cell Fractionation - Filtration
The Homogenised cell solution is filtered through a gauze to separate large cell debris or tissue debris, like connective tissue, from the organelles. The organelles are much smaller so they pass through.
Cell Fractionation - Ultracentrifugation
- The Filtrate is centrifuged at low speed so the densest organelles (Like nuclei) are separated first into a pellet (Dense material at the bottom of the test tube) The rest of the organelles stay suspended in the fluid - known as the supernatant
- The Supernatant is removed and centrifuged again at a higher speed for a longer time. This process is repeated for higher and longer times until the organelles are separated according to their density
Faster and longer centrifugation forces least dense organelles to be the pellet as it takes more force to pull the less dense organelles to the bottom
Order of organelles which are separated out according to their density
Nuclei Chloroplasts - if plant cell Mitochondria Lysosomes Ribosomes
The Cell cycle
- Consists of a period of the cells growing and new organelles and proteins being made = G1
- Then interphase, where the cell replicates its DNA, ready to divide = S (Synthesis) phase
- Then a Gap Phase (G2) where the cell keeps growing and the proteins needed for cell division are made, ready for Mitosis to occur
What happens during Interphase?
The cell carries out normal functions, but also prepares for division, as the DNA is unravelled and replicated, to double the genetic content. Organelles are also replicated and ATP content us increased.
Why is Mitosis needed?
Mitosis is needed for multicellular organisms growth and repair of damaged tissues.
The structure of chromosomes
The chromosomes are made of two strands, called chromatids, joined in the middle by a centromere. The two strands on the same chromosome are called sister chromatids. There are two strands as each chromosome has already made an identical copy of itself during interphase. Once mitosis is over, the chromatids end up as one-strand chromosomes (One chromatid, with a centromere) in the new daughter cells.
Prophase (Pro = before)
The chromosomes condense, getting shorter and fatter. Tiny bundles of protein called centrioles start moving to the end of the cell, forming a network of protein called the spindle. The nuclear envelope begins to break down
Metaphase (M= Middle)
The Chromosomes line up in the centre of the cell. The nuclear envelope has completely gone and the spindles attach to the centromeres
Anaphase (A = Away)
The Spindle fibres contract, splitting the centromeres, pulling the chromosomes (Identical chromatids) apart
Telophase
The chromatids reach the opposite poles on the spindle, they uncoils and become long and thin again. They are now called chromosomes again. The nuclear envelope forms around each group of chromosomes. The spindle fibres disappear/disintegrate
Cytokinesis
The cytoplasm splits, splitting the two nuclei apart, producing two genetically identical daughter cells. Mitosis is finished and the daughter cells starts the interphase part of the cell cycle for the next round of mitosis
Cancer and its treatment
Cancer is caused by a mutation of the genes that regulates mitosis and the cell cycle, leading to uncontrolled cell division, and eventually a tumour is formed. The treatment of cancer often involves disrupting the cell cycle so the cell division/cancer is prevented.
- Some chemical drugs prevent the synthesis of enzymes needed for DNA replication during Interphase. If they aren’t produced, it stops the cell from entering S phase - forcing the cell to kill itself
- Radiation can damage DNA at several points, and if the cell detects this, it will kill itself
- Inhibiting Metaphase by interfering with spindle formation
Mitotic Index
Number of cells with visible chromosomes / Total number of cells
Preparing a Root tip cell squash
- Add some 1M Hydrochloric acid to a boiling tube, and place it in a water bath at 60 degrees
- Using a scalpel, cut 1cm of the tip from a growing root
- Put the root tip into the boiling tube of acid and incubate for 5 mins. After this, remove the tip using tweezers and pipette water over the tip to wash it. Leave to dry.
- Place the tip on a microscope slide and cut 2mm from the very tip of it. Break the tip open and spread the cells out thinly using a mounted needle, Then add a few drops of stain and leave for a few mins.
- Place a cover slip over the cells and put a piece of folded filter paper on top. Squash the coverslip down to make the tissue thinner, allowing light to pass through it - don’t smear the coverslip though, as this will damage the chromosomes
Using an Optical microscope
- Start by clipping the slide onto the stage.
- Select the lowest-powered Objective lens.
- Use the Coarse adjustment knob to bring the stage up to just below the objective lens
- Look down the eyepiece (which contains the ocular lens). – Use the Coarse adjustment knob to try and move the stage downwards, to focus the image
- Adjust the focus with the fine adjustment knob until a clear image is seen
- If a greater magnification is needed, swap to a higher-powered objective lens and refocus
Calculating the actual size of cells
An Eyepiece graticule is fitted onto the eyepiece. It is like a transparent ruler, but with no units. The Stage micrometer is placed on the stage - It is a microscope slide with an accurate scale (with units) and can be used to work out the value of each division on the eyepiece graticule at a particular magnification. This means if the stage micrometer is removed and a specimen is placed on the stage, using the eyepiece graticule (now with known units for that particular magnification) you can measure the size of the cells
