Viruses and Cells Flashcards
What are the steps followed in Bacteriophage Reproduction?
- They attach to the Bacterial Cell using their Tail Fibers
- DNA is injected into the Bacterium
- Phage DNA and proteins are made
- New Phages are Assembled
- The Bacterium lyses (splits) and the new Viruses are released
Why are Viruses considered by many Scientist to be Non-Living?
They lack a Cellular Structure and can only carry out one of the characteristics of life which is Reproduction
What are the Two types of Viruses we study?
Bacteriophages and Retroviruses
What is the Host Cell required for Bacteriophages (Phages) to reproduce?
A Bacterium
What type of Virus is HIV an example of?
A Retrovirus
What does HIV stand for?
Human Immunodeficiency Virus
What Host Cell does the HIV virus target?
The Helper-T Lymphocyte
What effects does HIV have on a sufferer’s Immune System?
The Immune System is weakened and the individual is left susceptible to opportunistic infections
What Enzyme does the HIV virus require and why does it need it?
Reverse Transcriptase, it needs this to convert its RNA to DNA
What are the Similarities between Bacteriophages and HIV?
- Very small
- Essentially Non-Cellular
- Contain Genetic material within a protein coat
What are the Differences between Bacteriophages and HIV?
- Different Shapes (and Phages have tail fibers attached to a base plate, which are important in attaching the virus to bacterial cells)
- In HIV the protein coat/head is within a Phospholipid bilayer (no lipid bilayer in Phages)
- Glycoproteins are present in HIV but not in Phages
- Bacteriophages normally contain DNA while HIV contains RNA
- HIV contains Reverse Transcriptase (normally not present in Phages)
What are the Advantages of the Light Microscope?
- Living material can be observed
- Natural colour of the specimen can be observed
- Biological processes can be observed
What are the Disadvantages of the Light Microscope?
- The Maximum magnification is approx. x2000
What are the Advantages of the Electron Microscope?
- Magnifies the object up to x500,000
- Far greater resolution
What are the Disadvantages of the Electron Microscope?
- Only dead material can be observed
- Images are in black and white (any colour is added after “False Colour”)
- Lots of preparation is required which can cause “Artefacts”
What are the two types of Electron Microscope?
Transmission EM and Scanning EM
Describe Transmission EMs
- Electrons pass through a very thin specimen
- Images have high resolution
- Produces images with very high magnifications
Describe Scanning EMs
- Electrons bounce off the surface of the image
- Lower resolution and magnification
- Produces a 3D image of the surface
Describe Prokaryotic Cells
- No nuclei
- No membrane bound organelles
- DNA is circular
- DNA is naked
- Ribosomes are smaller than those found in Eukaryotic cells
- Plasmids are often present
- Cell wall is made of Peptidoglycan
- No microtubules
Describe Eukaryotic Cells
- Possess a nucleus
- Possess membrane bound organelles
- Have Chromosomes (DNA in a helix)
- Chromosomes contain a protein called Histone
Describe the Cell Structure of Plant Cells
- Cellulose cell wall which is fully permeable
- Chloroplasts for Photosynthesis
- Large permanent vacuole which is important in turgor support
- Cells joined by middle lamella - made up of calcium pectate
- Store starch
- No lysosomes or centrioles
Describe the Cell Structure of Animal Cells
- Never has a cell wall
- No Chloroplasts so no photosynthesis
- Small temporary vacuoles
- Possess centrioles which are used in nuclear division
- Store Glycogen
- Have Lysosomes and centrioles
Describe the Cell Structure of Fungal Cells
- Chitin cell wall
- No Chloroplasts so no photosynthesis
- Possess vacuoles
- Cells often multinucleate as new cell walls don’t always want to form
- Store Glycogen
- Have lysosomes
What are Plasma Membranes and what do they do?
- The boundary of the cell with the outside world
- The boundary of the organelle with the cytoplasm
- They contribute to the structure of organelles within the cell
What are the two basic components in a “Fluid-Mosaic” model?
Phospholipids and Proteins
Describe Phospholipids (in Plasma Membranes)
- Have a “Water loving” face (outwards)
- Have a “Water hating” face (inwards)
- Contains two layers of phospholipid molecules
- Semipermeable and separates the outside of the head from the inside of the head
Describe Proteins (in Plasma Membranes)
- Can be intrinsic, extrinsic or transmembrane and have various functions
What is the function of the Phospholipid Bilayer in the membrane?
- Allows the membrane to be selectively permeable
What is the function of Cholesterol in the membrane?
- Increases membrane stability
- Makes the membrane more fluid at high temperatures and more fluid at low temperatures
What are the functions of Protein in the membrane?
- Stability - helps to ‘anchor’ the Phospholipids
- Enzymes
- Adhesion sites - helps to hold adjacent cells together
- Recognition for hormones
- Antigens - in the immune response
- Protein channels - to allow polar molecules to cross the hydrophobic center of the membrane. They have a hydrophylic channel running through them
- Carrier proteins - these carry specific ions and molecules across the membrane. It might be because the molecule is large and charged or moving against the concentration gradient
What is the function of Glycocalyx in the membrane?
- Glycoproteins and glycolipids are always found on the outside of the cell surface membrane
- They are involved in cell to cell recognition which allows similar cells to form tissues
- Some glycoproteins act as antigens
- They act as receptor sites for specific molecules (complementary shape)
- They can form hydrogen bonds with water molecules to help stabilise the membrane
What are the functions of the nucleus?
- Most obvious organelle
- Contains chromosomes which code for proteins
- Chromosomes consist of DNA and a protein called Histone
- The nucleolus is an even darker area within the nucleus. It makes ribosomal RNA (rRNA). This is used to make ribosomes
- Nuclear pores allow for a copy of the DNA code to move out of the nucleus and into the cytoplasm
- The nuclear envelope is made up of two membranes. The outer membrane has ribosomes and is the site of origin of rough endoplasmic reticulum
What are the functions of the Endoplasmic Reticulum?
- A membrane system throughout the cell which forms flattened sacs (called cisternae)
- Some of the ER has ribosomes attached (Rough ER) and some doesn’t (Smooth ER)
- Rough ER acts as a “Scaffold” for the ribosomes to make protein. The protein then enters the rough ER and moves through the cisternae
- At the end, vesicles “pinch off” and fuse with the Golgi Apparatus
- Smooth ER makes lipids and cholesterol
What are the functions of Ribosomes?
- Very small organelles
- Can be free in the cytoplasm or attached to ER (rough ER)
- Made of two parts - protein and rRNA
What are the functions of the Golgi Apparatus?
- A series of curved flattedned sacs (called cisternae)
- Vesicles pinch off from the Rough ER and join with the forming face of the Golgi Apparatus. These vesicles contain protein
- The proteins are modified in the Golgi Apparatus (eg. they may have a carbohydrate chain added to form a glycoprotein)
- The modified protein moves to each cisternae in turn via vesicles
- Finally, vesicles pinch off the maturing face
- The vesicles can transport the protein within the cell or move to the plasma membrane and release their contents out of the cell by exocytosis (secretory vesicles)
What are the functions of Lysosomes?
- Tiny vesicles
- Formed by the Golgi Apparatus and contain hydrolytic enzymes for internal use in the cell
- They fuse with other vesicles containing something that has to be digested
- They have an important role in Phagocytes
What are the functions of Mitochondria?
- Typically “sausage shaped” with a double membrane or envelope
- The inner membrane is highly folded to form cristae that extend into the matrix to increase the surface area (for attachment of enzymes)
- Site of aerobic respiration (make ATP)
- They can contain some mitochondrial DNA
What are the functions of Microtubules?
- Hollow cylinders made of a protein called tubulin
- They are found in the centrioles and make the spindle fibres needed in mitosis
- They form part of the cytoskeleton which helps to support the cell and also to move vesicles and other substances around a cell
- They are also found in cilia and flagella
What are the functions of the Plasmodesmata?
- These are strands of cytoplasm that extend between neighbouring plant cells
- They allow molecules to pass through
What are the functions of Chloroplasts?
- They have a double membrane or envelope which encloses a liquid called the stroma
- The stroma contains a system of membranes called Thylakoids and these can be stacked to give Grana
- Chlorophyll is found on the surface of the Grana and it is here that light is absorbed for photosynthesis
- Starch grains and lipid droplets are also often found
