Assalamualaikum.
CHAPTER 4 : CHEMICAL COMPOSITION OF THE CELL
-Element =substance composed of only one kind of atom
-Elements in the cell -most common à C , H , O , N <= 96% of mass of human body
-others à Ca , P , Na , K , Fe , S , Mg , Cl <= 4% of mass of human body
-Trace elements (required in small quantities = 0.01%)
àFe , Mn , Co , Cu , I , Bo , Cr , Mo , Se , Fl
-Organic compound = chemical compound that contain C
-Organic compounds in the cell -->Carbohydrate , Proteins , Lipids , Nuclei acids
-Water ( H₂O) an inorganic compound , is important to our cell
Importance of organic compound in the cell
Carbohydrate -starch -glycogen -cellulose | -primary source of energy ( 17kJ/g ) -starch = main energy store in plants -glycogen = main energy store in animals -cellulose = main components in cell walls = important constituent of dietary fibre |
Proteins | -Build new cells for growth & renew damaged tissues -required in synthesize of enzymes , antibodies & certain hormones -form components of plasma membrane -involve in synthesize of haemoglobin in RBC |
Lipids -fats -phospholipids -oils -wax -steroid | -source of energy ( 38kJ/g ) -As solvent for fat-soluble vitamins – ADEK -phospholipids form components of plasma membrane -wax on the cuticle of a leaf prevent - water loss - infection by pathogens -steroid - eg : cholesterol , testosterone , oestrogen , progesterone -adipose tissue underneath the skin -insulates animals bodies against low temperature -adipose tissue lining the organs – protect major organs in the body |
Nuclei acids  Double helix DNA | -store genetics information in the form of code pentose sugar + phosphate group + nitrogenous base  -2 types DNA & RNA -DNA =genetic material that organism inherit from their parents -found in nucleus , chloroplast & mitochondrion -RNA =genetic material for some viruses -found in cytoplasm , ribosomes and nucleus |
Importance of water in the cell
-70% weight of human body consists of water
-70% - 90% weight of a cell made up of water
1) Medium for biochemical reaction
-most biochemical reaction in cell only occur if there is water
Eg: breaking down of protein , sugar & lipids
2) Solvent
-water is a polar molecules that attract one another & attract other ions
=> water can dissolve many ionic compound eg: salt & polar molecules eg: sugar
=> water is the universal solvent
3) Transport medium
-Blood plasma = 90% water
-Blood plasma contain sugars, amino acids , O₂ , CO₂ that dissolved in water
-Water transported these substances in the body
-Waste product – urea excreted from the body through urine
4) Maintaining osmotic balance and turgidity
-In animal – concentration of dissolved inorganic salt in water is important to maintain
osmotic balance between blood & interstitial fluid
-In plants – cell sap in the vacuole contains water & other dissolved substances.
This is important to maintain its cell turgidity.
-Turgidity provides support to plants.
5) Providing support
-Water supports the structure of a cell because 90% of the protoplasm is made up of water
6) Providing moisture
-water provide moisture to respiratory surfaces eg: alveoli.
-this enable the exchange of respiratory gases more efficient
7) Maintain body temperature
-water helps distribure the heat in the body
-excess heat eliminate from the body through – perspiration, urination and defaecation
-evaporation of sweat dissipates body heat, then cool the body surface
-evaporation of water from plants through transpiration keep plant tissues cool
8) High cohesion
-High cohesion = water molecules stick to each other
=>water can move in long, unbroken column through vascular tissue
=>maintain a continuous flow of water up the stem to the leaves
9) Lubrication
-Mucus & synovial fluid consists mostly of water
-Interstinal tract => mucus assists the movement of food substances
-Joints => synovial fluid lubricate the joints to ease the movement of joints
4.2 CARBOHYDRATES
-consists of C H O
-ratio of H : O is 2 : 1
-3 types of carbohydrates
a) Monosaccharides
-known as simple sugar
-main souce of energy for many cells
-long chain can combine with : protein àglycoproteins
: lipid à glycolipids
Glucose - plants & fruits
Galactose - milk
Fructose - fruit & honey
-Reducing sugar
b)Disaccharide
-combination of 2 monosaccharides
condensation
hydrolisis
condensation
hydrolisis
condensation
Hydrolisis
-Maltose -malt sugar
Lactose -milk sugar
Sucrose -cane sugar
-Maltose & Lactose – reducing sugar
-Sucrose - non reducing sugar
c)Polysaccharides
-combination of many monosaccharides
-insoluble in water due to large molecular size
-do not taste sweet
-do not crystallise
-Glycogen - in animal & yeast
Starch -in plants – bread,rice,wheat ,potatoes
Cellulose -plant cell wall
hydrolysis
4.3 PROTEINS
-consists of C H O N & sometimes S P
-made of monomer units called amino acids
- 20 types of amino acids in living cell
-dipeptide = 2 amino acids molecules link together by a peptide bond
Condensation
Hydrolysis
-2 groups of amino acids
Essential amino acids | Non-essentials amio acids |
1. Cannot be synthesised by the body | 1. Can be synthesised by the body |
2. Can be obtained from diet | 2. Derived from other amino acids |
-Animal protein – contain all essential amino acids
=> animal protein = first class protein
-Plant protein – Do not contain all essential amino acids
=> plant protein = second class protein
Protein Structures
-Protein can be grouped into 4 levels of organisation according to their structure
a) Primary structure
-linear sequence of amino acids in a polypeptide chain
-different types of protein have different sequence of amino acids
b)Secondary structure
-Coiled polypeptide chain forming alpha-helix chain or folded into beta-pleated sheets
-the alpha-helix & beta-pleated sheet structures are held together by H bonds
c)Tertiary structure
-refers to the way the helix chains or the beta pleated sheets are folded into a 3-D shape
-eg: Enzymes , hormones , plasma proteins , antibodies
d)Quarternary structure
-refers to the combination of 2 or more tertiary structure polypeptide chain forming large
and complex protein
-eg: Haemoglobin
4.4 LIPIDS
-consists of C H O & sometimes N P
-types of lipid
a)Fats & Oils
- triglyceride = consists of 1 molecule of glycerol & 3 molecules of fatty acid
-Fatty acid are either saturated or unsaturated
Saturated Fats | Unsaturated fats | |
Animal | Source | Plant |
Solid form | Room temperature ( 28⁰C ) | Liquid form |
None | Double bonds between C atoms | At least one (1 =monounsaturated fats) (2/> = polyunsaturated fats) |
Maximum | Number of H atoms | Not maximum |
No | Can form any chemical bond with other atoms? | Yes |
More | Cholesterol | Less |
Animal fats - butter | Example | Vegetable oil – corn oil |
b)Waxes
-long chained molecules => these cause wax to be waterproof
-found on cuticle of the epidermis of leaves, fruits & seeds of some plants
=>preventing the entry & evaporation of water
-found in sebum (extracted from oil glands) =>wax soften our skin
c)Phospholipids
-main components of plasma membrane
d)Steroids
-complex organic compound – eg: cholesterol , progesterone , testosterone , oestrogen
4.5 ENZYMES
The role of enzymes in organisms
-Many biochemical processes ( metabolism ) occur in a cell simultaneously
-Metabolism includes a)Anabolism – build complex molecules. Eg: photosynthesis
b)Catabolism – break down complex molecules. Eg: Digestion
-Metabolism reaction : reaction (regulated by enzymes)
-Enzymes = Biological catalyst that speed up biochemical reactions in the cells
General characteristics of enzymes
a)All enzymes are proteins
b)Enzymes speed up or alter the rate of chemical reactions
d)Enzymes remain unchanged at the end of the reactions
e)Enzymes are highly specific
-each enzyme can only catalysed one kind of substrate
-enzymes have specific sites which bind to specific substrates
Eg: Amylase only catalysed Starch
Only Starch can fit into the active sites of Amylase
f)Enzymes needed in small quantities only
-the same enzymes can be use over and over again to catalysed a large quantities of
substrate
-eg:
insulin
<------------------------
h)Enzyme’s activity can be slowed down or completely stopped by inhibitors
-eg of inhibitors= Mercury , Lead
i)Some enzymes need helper molecules called cofactor
-Eg of cofactor: Fe , Cu (inorganic) , Vit B (organic)
-cofactor bind to the enzyme and help to weaken bonds in substrate molecules
Intracellular and Extracellular enzymes
-Intracellular enzymes = enzymes which are produced and retained in the cell for the use of
the cell itself
-found in cytoplasm , nucleus , mitochondria & chloroplast
-Extracellular enzymes = enzymes which are produced in the cell but secreted from the cell
to work externally.
Eg: Trypsin produced by the pancreas but used in the duodenum.
Production of extracellular enzymes
 | Nucleus contains DNA. DNA contains information for the synthesis of enzymes. |
Ribosomes synthesise proteins which will be transported through spaces within the RER | |
Proteins depart from RER, wrapped in vesicles that bud off from membranes of the RER | |
The vesicles then fused with the membrane of Golgi apparatus and empty their contents into the membraneous space | |
Proteins futher modified during their transport in the Golgi apparatus. Eg: carbohydrate added to protein to make glycoprotein | |
Secretory vesicles containing these modified proteins bud off from the Golgi apparatus and travel to plasma membrane | |
These vesicle then fuse with plasma membrane before releasing the proteins outside the cell as enzymes |
The mechanism of enzyme action (Lock and Key)
Factors affecting enzyme activity
a)Temperature
-low temperature => subtrate molecules move at a slow rate
=> enzyme-catalysed reaction slow
-high temperature => substrate molecules moves faster
=> collision between substrate and enzyme molecules increases
=> chances of substrate coming into contact with active sites of enzyme also increase
-At higher temperature the rate of reaction between the substrate and enzyme increases until optimum temperature reached.
-At optimum temperature (mostly 37⁰C) an enzyme catalyses a reaction at maximum rate.
-At temperature higher than optimum temperature the rate of enzyme activity decreases because
- chemical bonds holding enzyme molecules begin to break
ð 3D shape of the enzyme will be altered
ð Destroy the enzyme active sites
ð Substrate can’t fit into the active sites
ðEnzyme lose its ability
-Denaturation is irreversible
b)pH
-Different enzymes may need different pH value to function optimally
Eg: Pepsin – pH 2 – can only function in acidic condition
Trypsin – pH 8.5 – can only function in alkaline condition
-A change in pH alter the charges on the active sites of the enzymes and substrate
surfaces
=> reduce the ability of both molecules to bind
-The efect of pH on enzymes are normally reversible
c)Substrate concentration
-if concentration of substrate increase
=> more substrate will bind with enzyme
=> more chances of collision between substrate and enzyme
=> rate of reaction increase
=> more products will be produced
-when rate of reaction reach a maximum rate
=> all enzyme’s active sites are filled
=> enzyme are saturated
=> enzyme concentration become a limiting factor
-Increasing enzyme concentration can futher increase the rate of reaction
credit to : Teacher Agnes Mojini
