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Biology AQA A level Bonding essay
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Essay of 3 pages for the course Biology Essay at AQA (achieved 24/25)
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Write an essay on the importance of bonds and bonding in organisms.Bonding is important in the release of energy from ATP. ATP hydrolase catalyses the
reaction where a phosphate is removed from ATP to form ADP and Pi. This breaks a high
energy bond releasing energy for many metabolic reactions within an organism. For
example, ATP is used to provide energy to actively transport substances against a
concentration gradient. Active transport is an important process in the absorption of glucose
and amino acids from food into the body by cotransport. This occurs in the ileum of the small
intestine. The epithelial cells of the ileum contains sodium potassium pumps on their cell
surface membranes which use energy from ATP to actively transport sodium ions out of the
cell creating a concentration gradient where the epithelial cells have a lower concentration of
sodium ions than it’s surroundings. This means that sodium ions move back into the cell via
facilitated diffusion, carrying amino acids or glucose with them down the concentration
gradient. It is important for amino acids and glucose to be absorbed into the body as amino
acids are required to synthesis proteins such as hormones and neurotransmitters, and
glucose is used as an energy store for both aerobic and anaerobic respiration.
In carbohydrates, there are glycosidic bonds between monosaccharides which allows them
to join up to form disaccharides and polysaccharides. These glycosidic bonds are part of
determining the structure and function of the polysaccharides. Starch is the stored form of
alpha glucose in plants. It is adapted to its function because it is made up of 2 types of
polymers: amylose and amylopectin. Amylose contains only 1,4 glycosidic bonds so is a
helical structure, this makes it adapted to storing energy compactly in cells in the form of
glucose. Amylopectin contains both 1,4 and 1,6 glycosidic bonds so is a branched structure,
this makes the glucose on the ends of the branches very accessible as they can be easily
removed by hydrolysis to be used in respiration - providing a rapid supply of energy.
Cellulose is another polysaccharide in plants. It is formed by the condensation reactions of
beta glucose molecules which are held together by 1,4 glycosidic bonds. To form the 1,4
glycosidic bonds, every other beta glucose monomer is rotated 180 degrees so that the
hydroxyl groups face outwards. This means that the straight chains of cellulose form many
hydrogen bonds across the hydroxyl groups which makes cellulose very strong. This makes
cellulose adapted to its function of making up cell walls as cell walls maintain the shape of
the cell by providing structural support. Cellulose also has high tensile strength which is
important so that cell walls can withstand the pressure from a plant cell becoming turgid
without breaking.
In proteins, bonding between chains of amino acids affect the shape and function of the
protein. Condensation reactions form peptide bonds between amino acids to make a
sequence of amino acids - forming the primary structure. Depending on the sequence of
amino acids, hydrogen bonds form at different points between the amino acids in the chain
allowing it to fold into alpha helix or beta pleated sheet shapes - this makes up the
secondary structure of the protein. Proteins are folded further as hydrogen bonds, ionic
bonds and disulphide bridges form between the chains and this makes up the tertiary
structure as well as decides the 3D structure of the protein. 2 or more separate amino acid
chains can form interactions together to form one protein to make up the quaternary
structure. The structure and 3D shape of the protein is important because it can allow or
inhibit the protein from performing a function. Enzymes are proteins that can catalyse
reactions and they are specific to a substrate due to having an active site which is
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