Unit 2

• what are the differences between prokaryotic (P) and eukaryotic cells (E) ?

  P are smaller - E are larger

  P has circular DNA - E has linear DNA

  only E has DNA associated with histones
• what is the function of the nucleus

  contains genetic information and has the nucleolus which makes ribosomes
• what is the function of ribosomes

  site of protein synthesis
• what is the function of the smooth endoplasmic reticulum

  make and store lipids
• what is the function of the Golgi apparatus

  package and modify proteins / lipids into vesicles by adding carbohydrates

  make lysosomes
• what is the function of the rough endoplasmic reticulum

  where proteins are made and stored

  have ribosomes on their surface

  proteins packaged into vesicles for transport
• explain the advantage of using an electron microscope

  electrons have a shorter wavelength than light so electron microscopes have a higher resolution
• how are antibodies produced in the body following a viral infection

  the virus contains an antigen

  the T-cells detect the antigen and release cytokines

  cytokines stimulate b-cells

  clonal selection b-cells divide by mitosis to produce clones

  plasma cells and b-memory cells produces antibodies

  antibodies are specific to the antigen

  antibody-antigen complex formed
• name the components that form the nucleus

  nuclear envelope

  nucleolus

  nucleoplasm

  chromatin
• Give structures found in all prokaryotic cells and in all eukaryotic cells.

  cell membrane

  ribosomes

  cytoplasm

  DNA
• what is an antigen

  foreign protein that stimulates an immune response / production of an antibody
• Contrast the structure of a bacterial celland the structure of a human cell.

  bacteria is smaller

  bacteria have a cell wall human cells dont

  bacteria has plasmids but human cells have nucleus

  bacterial lacks membrane-bound organelles but human has membrane-bound organelles

  bacterial have 70S ribosomes whereas human have 80S ribosomes
• Cristae

  extensions of the inner membrane

  extend across the whole width of mitochondria

  provides large surface area for attachment of enzymes involved in respiration
• Define "resolution"

  The minimum distance apart that two objects can be in order for them to appear as seperate items
• Define monoclonal antibodies

  Antibodies produced from a single clone of B cells
• Describe active transport.

  carrier proteins

  against concentration gradient

  using ATP
• Describe binary fission in bacteria.

  circular DNA and plasmids are replicated

  cytoplasm divides

  each daughter cell has : one copy of circular DNA and a variable number of plasmids
• Describe the function of cholesterol in the cell membrane

  reduces lateral movement of other molecules including phospholipids

  makes the membrane less fluid at high temperatures

  prevent leakage of water and dissolved ions from the cell as it is hydrophobic
• vacuole

  fluid filled ( cell sap )sac bound by a single membrane called the tonoplast

  provides structure to plant cell
• what is the cell wall of prokaryotic cells made of

  murein
• describe the structure of all viruses

  attachment proteins

  capsid

  genetic material e.g. mRNA or DNA
• define magnification

  how many time larger the size of the image is than the size of the object
• what are the features of a solution used for ultracentrifugation

  cold - prevent enzyme activity that may break down the organelles

  isotonic - prevents osmosis of water into organelles causing the organelles to burst as the water potential of the solution is equal to the water potential of the organelles

  buffered - maintain pH to prevent enzymes denaturing
• describe the process of ultracentrifugation

  homogenise the cells to break them open

  filter

  ensure the solution is cold isotonic and buffered

  centrifuge then remove nuclei

  centrifuge the supernatant at higher speed

  heaviest / most dense organelles will be at the bottom of the tube
• what property of cell organelles allow them to be centrifuged

  different densities
• how does a light microscope produced an image

  beam of light is shone through the specimen
• how does a TEM produce an image

  electromagnet focuses a beam of electrons onto specimen

  beam passes through the thin section of the specimen

  parts of the specimen that let electrons pass through appear light and the parts that absorb the electrons appear dark

  image photographed using microphotograph
• how does an SEM produce an image

  beam of electrons shone on surface of a metal-salt stained specimen

  electrons scattered onto the surface of the surface of the specimen

  electrons reflect back onto the detector

  computer analyses the pattern of scattered electrons

  3D image
• why use electron microscopes instead of light microscope

  electrons have a shorter wavelength than light

  so electron microscopes have a higher resolution
• disadvantages of TEM

  needs vacuum to be used - living specimens cannot be viewed

  images are black and white

  complex staining process

  only produces 2D images

  image may have artefacts

  specimen sample has to be thin
• disadvantages of SEM

  needs vacuum to be used - living specimens cannot be viewed

  images are black and white

  complex staining process

  image may have artefacts

  lower resolution than TEM

  cannot view the internal structure of samples e.g. organelles inside a cell
• describe the process of co-transport

  sodium ions are actively transported out of epithelial cell into the blood in capillaries

  concentration of sodium ions in the epithelial cell decreases

  sodium ions diffuse from the lumen down the concentration gradient into epithelial cells

  glucose attach to the co-transporter protein and are actively transported into the epithelial cell against their concentration gradient

  glucose moves by facilitated diffusion from the epithelial cell into the blood
• what are the stages of interphase

  G1 and G2

  S phase
• what occur during interphase

  protein synthesis

  chromosomes are uncondensed so not visible

  DNA unwound as chromatin so genes are accessible for transcription

  grows and makes enough organelles for two cells
• what occurs during S phase

  DNA replication

  DNA checked for errors to prevent mutations being passed on
• chromatin vs chromosomes

  chromatin - unwound DNA allows DNA replication

  chromosomes - condensed , tightly packed DNA
• describe the structure of an antibody and label the diagram

  produced by b-cells

  4 polypeptide chains

  chains joined by disulphide bridges

  unique 3D shape

  A) light chain

  B) heavy chain

  C) constant region

  D) variable region

  E) antigen binding sites

  
• what is an antibody

  a protein / immunoglobin specific to an antigen

  produced by b-cells
• compare passive (P) and active (A)immunity

  A requires exposure to an antigen P does not

  P protection is immediate

  A memory cells are produced

  A protection is long term as antibodies are produced in response to the complementary antigen being present in the body

  P protection is short term as antibodies are broken down
• describe give examples of active immunity

  immune system makes antibodies in response to an antigen

  natural - immune after catching a disease

  artificial - immune after vaccination