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IB  Standard  Level  Biology    
Chapter  2  –  Molecular  Biology    
 Chapter  2
...
       
 
 
 
 
 
 
 
 
 
 
 
 
Majority  of  molecules  in  all  living  organisms  can  be  categorized  into  four  biochemical  groups  
 

Molecules  

Subcomponents  (building  blocks)    Example  molecules  

Carbohydrates  

Mono/di/poly/saccharide’s  

Glucose,  ribose,  lactose,  starch  

Lipids  

Glycerol,  fatty  acids,  phosphate  
groups    

Fat  stored  in  adipose  cells,  some  
hormones    

Proteins  

Amino  acids  

Enzymes,  antibodies,  peptide  hormones  

Nucleic  acids    

Nucleotides    

DNA,  RNA,  ATP  

 
Carbohydrates    
•
Contain  carbon,  hydrogen  and  oxygen  
•
Organic  compounds  consisting  of  one  or  more  simple  sugars    
 
 

Monosaccharide  

Disaccharide  

Polysaccharide  

Subunits  

One  

Two  

Three  

Main  function  

Energy  source  

Transport  form  

Storage  form  

Examples  

Glucose  
Galactose  
Fructose  

Lactose    
Sucrose  
Maltose  

Cellulose  
Glycogen  
Starch  

Mnemonic  

Gives  Good  Flavour  

Length  Support  Movement  

Can  Get  Stored  

 

 
Metabolism  
 
 
 
 
 
 
 
 
 
 

IB  Standard  Level  Biology    
 

Chapter  2  –  Molecular  Biology    
 
Alpha  and  Beta  glucose  are  optical  isomers  
because  they  are  compounds  with  the  same  
chemical  formula  but  have  different  
arrangements  if  atoms  (different  
properties)  
 
 
 

 
 
Lipids  
•
Carbon  compounds  made  by  living  organisms  that  are  mostly  or  entirely  hydrophobic  
•
Insoluble  in  water  
•
Non  polar  (will  absorb  in  non-­‐polar  solvent)  
•
Molecules   can   be   identified   as   lipids   if   they   have   two   or   three   hydrocarbon   chains   or   the  
quadruple  ring  structure  of  steroids    
 
Triglycerides:    
^Largest  type  of  lipid    
3  fatty  acids  linked  to  glycerol  (join  by  condensation  reaction  so  they  have  3  hydrocarbon  tails)    
E
...
 Fats  and  oils  
 
 
 
 
 
 
 
 
 
Phospholipids:  
Two  fatty  acids  linked  to  glycerol  with  a  phosphate  group  instead  of  the  third  fatty  acid  
 

 

Steroids:  
Four  fused  rings  in  their  molecule    
E
...
 cholesterol,  progesterone,  estrogen,  testosterone  
 
Proteins    
• Amino  acids  form  proteins    
• All  proteins  contain  nitrogen  
• Composed  of  one  or  more  chains  (polypeptide  chains)  of  amino  acids    
• There  are  20  unknown  amino  acids    
 
 
 
 
 
 
 
Nucleic  Acids  
• Nucleotides  form  bonds  between  the  pentose  sugar  and  phosphate  group  to  form  long  
polynucleotides  chain  

IB  Standard  Level  Biology    
Chapter  2  –  Molecular  Biology    
 Chapter  2
...
 80%  of  a  human  cell  consists  of  water    
• Polar  covalent  bond    
• Water  molecule  joined  by  hydrogen  bonds  (weak  bonds)    
• Polymerisation  
• Oxygen  atom  is  slightly  negative/hydrogen  atoms  are  slightly  positive  
• Difference  between  solvent  &  solute  (solute  are  substances  that  were  dissolved  in  the  solvent)      
• Hydrophilic:  substances  that  are  chemically  attracted  to  water  (blood  is  95%  water-­‐  
glucose/amino  acids  can  dissolve  in  it)    
• Hydrophobic:  substances  that  are  insoluble  in  water  (oxygen  in  the  blood  won't  dissolve  
because  they  are  carried  by  haemoglobin)    
 
Properties  of  water  
• Thermal-­‐  high  heat  capacity  (breaking  of  bonds)    
• Adhesion-­‐  water  molecules  bonding  to  another  substance    
• Cohesion-­‐  sticking  to  one  another  (water  molecules  sticking  to  another  water  molecule)  
• Coolant-­‐  a  lot  od  energy  required  to  change  from  solid  to  gas
...
g
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3  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Carboxyl  
 
group  
 
 
 
 
Saturated    
Connected  by  a  single  covalent  bond  (max  amount  of  
carbons  +  hydrogen)  
Unsaturated  
Contain  one  more  double  bonds    
Monounsaturated  

Only  one  double  bond    

Polyunsaturated  
Two  or  more  double  bond  
Cis  unsaturated    
Same  side  of  a  double  bond      
Trans  unsaturated     Opposite  side  of  a  double  bond    

 

IB  Standard  Level  Biology    
Chapter  2  –  Molecular  Biology    
  Cis-­‐isomers  

Trans-­‐isomers  

 

 

Very  common  in  nature  

Rare  in  nature  –  usually  artificially  produced  to  
produce  solid  fats,  e
...
 margarine  from  vegetable  
oils
...
4  
• Ribosomes  are  a  form  of  RNA  (rRNA)  during  transcription    
• 20  amino  acids:  "r"  group  give  them  different  properties  e
...
 positive/negative  charge  and  
hydrophilic/hydrophobic    
• Primary  structure:  
• Secondary  structure:  
• Tertiary  structure:  
• Quatemary  structure:    
• Difference  between  Fibrous  protein  and  globular  proteins    
 
Properties   Fibrous  Protein  
Globular  Protein  
Shape  
Long  and  Narrow  
Rounded/  spherical  
Role  
Structural  (strength  and  support)  
Functional  (catalytic,  transport,  etc
...
  More  sensitive  to  changes  in  heat,  pH,  etc
...
 Absorbs  a  single  photon  of  light    
• Collagen:  involved  in  holding  teeth  in  place,  strong  mesh  
• Spider  silk:  stronger  than  Kevlar    
   
• Genome:  all  of  the  genes  of  an  organism    
• Proteome:  all  of  the  proteins  of  an  organism    

IB  Standard  Level  Biology    
Chapter  2  –  Molecular  Biology    
 Chapter  2
...
6  
   
 
Bases  

Sugar  

RNA  
Adenine  (A)  
Guanine  (G)  
Uracil  (U)  
Cytosine  (C)  

DNA  
Adenine  (A)  
Guanine  (G)  
Thymine  (T)  
Cytosine  (C)  

 
 

 
 

 
 
 
 
Number  if  strands  
 
 
 
 
 
 

Single  Stranded,  and  often,  but  not  
always,  linear  in  shape  

Two  anti-­‐parallel,  complementary  strands  
form  a  double  helix    

IB  Standard  Level  Biology    
Chapter  2  –  Molecular  Biology    
  Double  helix  is  antiparallel  
 
Purines  
(longer)  pyrimidine’s  (shorter)    
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
Chapter  2
...
coli  plasmid    

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
Outline  of  translation    
1
...
The  mRNA  contains  a  series  of  codons  each  of  which  codes  for  an  amino  acid    
3
...
 tRNA  
molecules  bind  to  specific  amino  acid  that  corresponds  to  the  anticodon  
4
...
The  ribosome  moves  along  the  mRNA  and  presents  codons  in  the  first  two  binding  sites    
6
...
A  peptide  bond  is  formed  between  the  two  amino  acids  (carried  by  the  tRNAs)    
8
...
Another  tRNA  carrying  an  amino  acid  binds  to  the  first  site  and  a  second  peptide  bond  is  
formed  
10
...
e
...
8  
• Cellular  respiration:  the  controlled  release  of  energy  from  organic  compounds  in  cells  to  
form  ATP  
• Order  of  energy  sources-­‐  glucose/carbohydrates  -­‐>  lipids/  fatty  acids  -­‐>  proteins    
   

 

•

ATP  is  used  for:  muscle  contraction,  active  transport,  protein  synthesis,  vesicle  transport,  
DNA/RNA  replication,  cell  signalling  

   
Anaerobic  respiration:  
• No  oxygen  present/  small  amount  of  ATP  produced  
• Bread:  oxygen  in  the  dough  is  used  up  so  yeast  is  forced  to  respire  anaerobically    
Bioethanol    
Lactate:  supply  ATP  very  quickly  in  aerobic  respiration  because  a  lot  of  ATP  is  produced  in  
this  process    
   

 

   

Chapter  2
...
   
Chlorophyll  absorbs  red  and  blue  light  most  effectively  and  reflects  green  light  more  than  
other  colours
...
 
Chloroplasts  are  the  tiny  organelles  in  plant  or  algae  cells  where  photons  (the  fundamental  particle  
of  light)  are  captured
...
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
★Definition  
Action  spectrum  shows  the  efficiency  of  photosynthesis  or  rate  of  photosynthesis  achieved  over  
the  various  wavelengths  of  light  from  the  visible  spectrum
...
   

 
 
 
 

 

IB  Standard  Level  Biology    
Chapter  2  –  Molecular  Biology    
 Photolysis  of  Water  
Photolysis  is  the  splitting  of  water  by  light  (photo  –  light  and  lysis  –  splitting)
...
 
Photolysis  generates  hydrogen  ions,  electrons  and  oxygen:  
2  H2O  +  photons  →  4e-­‐  +  4H+  +  O2  
The   electrons   are   used   to   generate   ATP   through   cyclic   or   non-­‐cyclic   photophosphorylation
...
 

 
Photosynthesis  carbohydrate  production:  

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

The energy absorbed from light is used to turn carbon dioxide and water into carbohydrates and
other carbon compounds
...
Light  dependent  reaction:  use  light  energy  to  produce  ATP  and  to  split  water  (photolysis)  
o Light  is  absorbed  by  chlorophyll,  which  results  in  the  production  of  ATP  (chemical  energy)  
o Light  is  also  absorbed  by  water,  which  is  split  (photolysis)  to  produce  oxygen  and  hydrogen  
o The  hydrogen  and  ATP  are  used  in  the  light  independent  reactions,  the  oxygen  is  released  
from  stomata  as  a  waste  product  
   
2
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g
...
)  
o The  ATP  provides  the  required  energy  to  power  these  anabolic  reactions  and  fix  the  carbon  
molecules  together  
 
 
 

IB  Standard  Level  Biology    
 

Chapter  2  –  Molecular  Biology    
 

 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

IB  Standard  Level  Biology    
Chapter  2  –  Molecular  Biology    
 Photosynthesis:  Limiting  factors    
★Definition
A limiting factor is a factor that restricts the rate of a reaction when present in low amount
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