Topic 2 - Cells Flashcards
What is the Golgi apparatus?
A series of fluid filled, flattened and curved sacs with vesicles surrounding the edges. It processes and packages proteins and lipids
Define cell fractionation
Cell fractionation is the process in which different parts and organelles of a cell are separated so that they can be studied in detail.
Give the first stage of homogenisation
The cells are first blended in an homogeniser forming the resultant fluid called the homogenate. This tube of homogenate is then placed in a centrifuge and spun at a low speed
Give the second stage of homogenisation
The heaviest organelles, the nuclei, are forced to the bottom of the tube where a thin sediment or pellet forms
Give the third stage of homogenisation
The fluid at the top, called the supernatant, is removed which leaves just the sediment of the nuclei. The supernatant is then transferred to another tube and spun at a slightly faster speed. This time the pellet that forms contains the next heaviest organelle, the mitochondria.
Give the fourth stage of homogenisation
This process continues so that each time the speed is increased the next heaviest organelle is sedimented and separated out
Give the conditions of the homogenate at the beginning of homogenisation and explain why
The homogenate at the beginning is placed in a cold, buffered solution of the same water potential as the cells. This is to prevent the organelles from bursting under osmotic pressure, to inactivate any enzymes from breaking down organelles and so that the pH does not fluctuate
What is the nucleus? (Talk about structure too)
Nucleus is a double membrane called the envelope containing - 3000 nuclear pores that enables molecules to enter and leave
It also contains chromatin and a nucleolus which is the site of ribosome production
What is the rough endoplasmic reticulum?
RER is a series of flattened sacs enclosed by a membrane with ribosomes on the surface
RER folds folds and processes proteins made on the ribosomes
What is the smooth endoplasmic reticulum?
SER is a system of membrane bound sacs
SER produces and processes lipids
What are mitochondria? (Discuss structure)
They are oval shaped, bound by a double membrane called the envelope
The inner membrane is folded to form projections called cristae with a matrix on the inside containing all the enzymes needed for respiration
What are centrioles?
Hollow cylinders containing a ring of microtubules arranged at right angles to each other
Centrioles are involved in producing spindle fibres for cell division
What are ribosomes?
Ribosomes are composed of two sub units and are the site of protein production
What are lysosomes?
Lysosomes are vesicles containing digestive enzymes bound by a single membrane
What are the two types of electron microscope?
Transmission and Scanning
State what happens in a Transmission Electron Microscope (TEM)?
A beam of electrons passes through thin section of a specimen. Areas that absorb the electrons appear darker on the electron micrograph that is produced
State what happens in a Scanning Electron Microscope (SEM)?
A beam of electrons passes across the surface and scatter. The pattern of scattering builds up a 3D image depending on the contours of the specimen
Give the limitations of an electron microscope
The whole system must be in a vacuum so living specimens cannot be observed
Specimens must be very thin, particularly for TEM so that electrons can pass through
What are viruses?
Viruses are non-living structures which consist of nucleic acid (either DNA or RNA) enclosed in a protein coat called the capsid, sometimes covered with a lipid layer called the envelope
State what happens in Interphase
The cell grows and prepares to divide - chromosomes and some organelles are replicated
State what happens in cytokinesis
The parent and replicated organelles move to opposite sides of the cell and the cytoplasm divides thus producing two daughter cells.
Describe what happens during Prophase
Nuclear membrane breaks down
Chromosomes condense
Spindle fibres appear
Describe what happens during Prometaphase
Spindle fibers attach to chromosomes
Chromosomes condense
Describe what happens during Metaphase
Chromosomes align
Describe what happens during Anaphase
Centromeres divide
Sister chromatids move to opposite poles
Describe what happens during Telophase
Nuclear membrane reforms
Chromosomes decondense
Spindle fibers disappear
Give the seven structures of a prokaryotic cell
Cell Wall
Capsule
Plasmid
Flagellum
Pili
Ribosomes
Mesosomes
What is the cell wall? (Bacteria)
Rigid outer covering made of peptidoglycan
What is the capsule?
Protective slimy layer which helps the cell to retain moisture and adhere to surfaces
What is the plasmid?
Circular piece of DNA
What is the flagellum?
A tail like structure which rotates to move the cell
What is the Pili?
Hair-like structures which attach to other bacterial cells
What are ribosomes?
Site of protein production
What are Mesosomes?
Infoldings of the inner membrane which contains enzymes required for respiration
What are the main molecules in cell membranes?
Phospholipids
What happens when cell surface membranes are in an aqueous environment?
Phospholipid molecules form a bilayer
A hydrophobic barrier is formed between the inside and outside of a cell
How are phospholipids arranged in a cell-surface membrane?
Hydrophobic tails orientated to the inside and the hydrophilic tails orientated to the outside
Give the functions of phospholipids in a membrane
Allow lipid-soluble substances to enter and leave the cell
Prevent water-soluble substances entering and leaving the cell
Make the membrane flexible and self-sealing
Give the purpose of surface proteins in a membrane
Occur in the surface of the bilayer never extend completely across it.
Give mechanical support to membrane or work in conjunction with glycolipids, acting as cell receptors for molecules such as hormones
Give the purpose of Protein Channels in a membrane
Form water-filled tubes
Allow water-soluble ions to diffuse across the membrane
Give the purpose of Carrier Proteins in a membrane
Bind to ions or molecules glucose or amino acids
Change shape in order to these molecules membrane
Give the three functions of Cholesterol in a membrane
Strengthen membrane - reduce lateral movement of other molecules including phospholipids, by pulling together fatty acid tails
Make the membrane less fluid at high temperatures
Very hydrophobic - Prevent leakage of water and dissolved ions from the cellG
What is a glycolipid?
Made up of a carbohydrate covalently bonded with a lipid
What allows the cell to receive certain chemicals?
The carbohydrate potion from a glycolipid extends from the phospholipid bilayer into the water environment outside the cell
Give the three functions of glycolipids
Act as recognition sites (antigens)
Help maintain stability of membrane
Help cells attach to one another to form tissues
What are glycoproteins?
A carbohydrate chain attached to an extrinsic protein on the surface of the membrane
Again, can act as cell-surface receptors, more specifically for hormones and neurotransmitters
Give the functions of glycoproteins
Help cells attach to one another to form tissues
Allow cells to recognise one another
What is diffusion?
The passive movement of small, non-polar, lipid soluble molecules from an area of high concentration to an area of low concentration
The molecules move directly through the phospholipid bilayer
What is facilitated diffusion?
Requires a channel protein in the cell membrane to transport polar molecules, charged and water soluble molecules across the membrane
What do exocytosis and endocytosis both do?
Transport large particles
The particles are enclosed in vesicles made from the cell surface membrane
State what happens during endocytosis
Particles are transported into the cell
State what happens during exocytosis
Vesicles containing large particles are fused with the cell surface membrane and released from the cell
What is Co-Transport?
Co-Transport uses ions to move substances into and out of cells
What is binary fission?
The process by which prokaryotic cells divide
Give the first stage of binary fission
The circular DNA in the cells replicates and both copies attach to the cell membrane
Plasmids also replicate
Give the second stage of binary fission
The cell membrane then begins to grow between the two DNA molecules and begins to pinch inwards, dividing the cytoplasm in two.
Give the third stage of binary fission
A new cell wall forms between the two DNA molecules dividing the original cell.
The identical daughter cells each have a single copy of the circular DNA and a variable number of copies
of the plasmids.
Define water potential
The pressure created by water molecules
What does pure water have a potential of?
Zero
What happens to the water potential when solutes are dissolved in it?
It becomes more negative. The more negative the water potential, the more solute must be dissolved in it.
What is an isotonic solution?
When the water potential is the same in the solution and the cell within the solution
What is a hypotonic solution?
When the water potential of a solution is more positive (closer to zero) than the cell
What is a hypertonic solution?
When the water potential of a solution is more negative than the cell
