Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, golgi apparatus, and plasma membrane

The rough endoplasmic reticulum produces the proteins to export, such as

digestive enzymes. They are then transported to the golgi apparatus to be

processed. The golgi apparatus prepares the substances for exocytosis by

wrapping it and creating a enclosed membrane. The vesicle moves

towards the plasma membrane along microtubules, and soon joins (fuses

into) it in order to release their contents to the outside. The flexibility and

fluidity of the plasma membrane allows this to happen.

Often the substances to release outside are proteins. Therefore, before the

process coming to the RER the transcriptions and translation might be

done first.

 

Describe how the fluidity of the membrane allows it to change shape, break, and reform during endocytosis and exocytosis. (Don’t forget to talk about the properties of the fatty acids that make up the phospholipids… e.g. trans/cis , saturated/unsaturated) Phospholipid bilayers consist of hydrophilic heads made from glycerol and phosphate, and hydrophobic tails that are fatty acids. Polar hydrophilic heads are attracted to the water while non-polar hydrophobic tails are repelled from the water. Several structures in the membrane that control its fluidity are the phospholipid molecules and cholesterol.

• Phospholipid molecules change places in the horizontal plane and this creates the fluid property of the membrane. However, molecule exchange does not occur vertically, which allows the integrity of the membrane.

• Cholesterol embedded between phospholipid molecules reduces its fluidity and maintains its shape.

Membrane is held together by the relatively weak hydrophobic association between phospholipids. This association allows fluidity and flexibility of membrane, allowing breaking and remaking of membranes and the control over entry and exit of substances in and out of the cell, mainly by endocytosis and exocytosis. The structures of fatty acids hugely affect the fluidity of the membrane. Phospholipids with short or unsaturated fatty acids are more fluid. Especially in unsaturated fatty acids, cis and trans fatty acids controls this. Cis fatty acids are double bonded, which gives a bent fatty acid. It is often liquid in water, which increases the fluidity of the membrane. However, trans fatty acids are straight and it is often solid in water. Since it is denser, the fluidity is decreased.

Figure 1 – Mechanism of membrane fusion and breakage

1. Two membranes approach. 2. Phospholipid heads flow together starting the process of fusion. 3. At the point of contact, there is a single bilayer. 4. The pore opens and the membranes are now continuous.

This allows vesicle membrane to fuse with the plasma membrane during exocytosis and vesicle formation by the in folding of the plasma membrane during endocytosis.

Katja  Frisinger        

Endocytosis  Endocytosis  is  a  process  by  which  uses  energy  to  absorb  molecules  by  engulfing  them  (Wikipedia  Contributors).  Cells  use  endocytosis  to  absorb  materials  that  would  otherwise  be  too  big  or  highly  polar  (Weem).  We  study  two  types  of  Endocytosis:  

Pinocytosis  Pinocytosis  is  when  the  cell  engulfs  liquids  (Weem).  

Phagocytosis  Phagocytosis  is  when  the  cell  engulfs  solids  (Weem).  

Process  1. Cell  has  a  receptor  and  wants  to  consume  a  particle  2. The  cell  membrane  bends  and  envelops  the  particle  within  the  membrane  3. The  membrane  recloses  with  the  particle  inside,  creating  an  intracellular  

vesicle.  The  cell  now  has  the  particle  within  it.  

 Process  of  Endocytosis  (Weem)  

Examples  While  I  haven’t  found  any  past  questions  that  are  straight-­‐up  asking  “Explain  endocytosis,”  there  are  many  multiple-­‐choice  and  essay  questions  in  which  the  mark  scheme  requires  you  to  reference  it,  so  here  are  some  examples:  

• Explain  the  function  of  vesicles  in  eukaryotic  cells.  (N08/4/BIOLO/HP2/ENG/TZ0/XX/M+)  

• Describe  how  phagocytic  leucocytes  may  act  as  a  defense  against  disease.  (M11/4/BIOLO/SP2/ENG/TZ2/XX/M)  

Works  Cited  Weem,  Minka.  Peeters.  Biology.  Victoria:  IBID  Press,  2008.  Print.  

Wikipedia  contributors.  "Endocytosis."  Wikipedia,  The  Free  Encyclopedia.  

Wikipedia,  The  Free  Encyclopedia,  30  Jan.  2014.  Web.  13  Feb.  2014.  

   

2.3.6 Outline two roles of extracellular components

- Cellulose is the best known example of an extracellular component in plant cells (Weem).- Examples in animal cells are bone, cartilage and connective tissue (Weem).

- Cellulose is the main component of plant cell walls(Click4biology).- It is a non-living secretion of the cell (Weem).- It maintains the shape of the cell (Click4biology).- It provides structural support (Click4biology).- It prevents excessive uptake of water by the cell (Click4biology).- The cell wall provides a barrier for pathogens so the cell recognizes the pathogens and

start responding (Weem).

Bibliography:

Click4biology. Click4Biology: 2.3 Eukaryotic cells. 14 Febuary 2014 <http://click4biology.info/c4b/2/cell2.3.htm#extra>.

Weem, Minka. Peeters. Biology. Victoria: IBID Press, 2008. Print.

Figure 1. Comparing prokaryotic and eukaryotic cells table (Weem).

Figure 2. Differences between plant and animal cells (Weem).

2.5.4  Describe  the  events  that  occur  in  the  four  phases  of  mitosis  Stage   Phase   Description  Mitosis  (Nuclear  division)    

Prophase   1.  DNA  supercoils  -­‐Chromosome  become  visible  -­‐Centrioles  move  to  opposite  poles  -­‐Spindle  formation  -­‐  Nucleolus  &  Nuclear  membrane  disappear  -­‐Each  chromosome  consist  of  2  identical  sister  chromatids  (held  together  by  centromere)  

Metaphase   -­‐Chromosomes  move  to  equator  -­‐Spindle  microtubules  attach  to  centromere  

Anaphase   -­‐Centromeres  separate  -­‐Chromatids  separate  &  move  to  opposite  poles  (chromosomes)  

Telophase   -­‐Chromosomes  arrive  at  poles  -­‐Spindle  disappear  -­‐Centrioles  replicate  (animal  cells)  -­‐Nuclear  membrane  &  nucleolus  reappear  -­‐Chromosome  become  chromatin  

 2.5.5  Explain  how  mitosis  produces  two  genetically  identical  nuclei  1. DNA  replicated  to  produce  2  copies  of  genetic  material  (during  interphase  S)  2. 2  identical  DNA  molecules  are  held  together  by  single  centromere  (sister  chromatids)  3. Sister  chromatids  separated  &  drawn  to  opposite  poles  of  cell  (during  mitosis)  4. Cell  division  (cytokinesis)  will  result  in  2  nuclei,  each  containing  one  of  each  pair  of  chromatids  

(equally  identical)    Paper  2  Question:  (a) Before  cell  division  in  unicellular  and  multicellular  organisms,  the  nucleus  must  divide  to  

produce  two  genetically  identical  nuclei.  Explain  the  events  that  occur  in  cells  that  result  in  the  production  of  genetically  identical  nuclei.  [8]  1. Mitosis  -­‐  DNA  replication;  each  chromosome  consists  of  two  sister  (identical  chromatids)  2. Chromosomes  supercoiling  3. Nuclear  membrane  breaks  down  4. Chromosomes  align  (at  equatorial  plate)  5. Spindle  fibres  (microtubules)  attach  to  centromeres  of  chromosomes  on  opposite  sides  6. Centromeres  split  à  chromatids  become  chromosomes;    7. sister  /  identical  chromosomes  pulled  to  opposite  poles;  8. Nuclear  membranes  reform;    9. events  correctly  assigned  to  interphase,  prophase,  metaphase,  anaphase,  &  telophase;    

(b) Explain  how  mitosis  produces  two  genetically  identical  nuclei.  [8]  1. During  interphase  DNA  replicates  /  produces  two  copies  of  genetic  material;    2. Sister  chromatids  are  two  identical  DNA  molecules  held  together  by  centromere;    

a. Separated  during  mitosis  to  form  two  genetically  identical  nuclei;  3. in  prophase  chromosomes  become  visible  as  double-­‐stranded  chromosomes  /  joined  sister  

chromatids;    4. Chromosomes  condense  by  supercoiling;    5. Chromosomes  attach  to  spindle  microtubules  at  centromeres;  6. Chromosomes  begin  to  move  towards  equator  /  centre  of  cell;    7. During  metaphase  all  chromosomes  lined  up  at  equator  separately  /  not  in  homologous  

pairs;  at  start  of  anaphase  centromeres  divide  separating  sister  chromatids;    8. Separated  sister  chromatids  known  as  (single  stranded)  chromosomes;    9. (Identical  sets  of)  chromosomes  pulled  to  opposite  poles;    10. Move  by  contraction  of  microtubules;    11. Nuclear  envelope  /  membrane  forms  around  each  set  of  chromosomes;  

 

OUTLINE ONE THERAPEUTIC USE OF STEM CELLS !what is a stem cell?

Stem cells are undifferentiated cells with the opportunity to become any type of cell. Once the differentiation has occurred, it cannot be reverse. They are categorised into pluripotent and embryonic. Being unspecialised, having the ability to divide repeatedly, able to become any type of cell, and have a large nucleus are what makes a stem cell different to other cells (Walpole).

!bone marrow transplant - leukaemia

Leukaemia is a type of cancer that overproduces white blood cells (leucocyte). The leucocytes become uncontrollable as they continuously grow and do not function properly. As a result it suppresses the growth of normal cells, thus leading to other problems (Chilvers). !To treat the cancer chemotherapy is a common method; it uses chemical substances to kill most of the abnormal cells and when they are not all killed bone marrow transplant is used. In this process the patient’s bone marrow stem cells are replaced with a donor’s (University of Utah). Figure 2 shows the possible differentiations a bone marrow stem cell is able to achieve, evidently lymphocytes is one of them. !After a successful transplant the stem cells will produce new, healthy cells replacing the abnormal, cancerous cells. !!

bibliography University of Utah. Stem Cells in Use. 6 January 2014. 13 February 2014 <http://learn.genetics.utah.edu/

content/stemcells/sctoday/>.

Walpole, Brenda. Biology for the IB Diploma . Cambridge: Cambridge University Press, 2011.

Chilvers, Osborne and Farr. The Oxford Dictionary. Oxford: Oxford University Press, 1997.

Figure 1 - Bone marrow cells differentiation (Walpole)