Metabolism
A set of enzyme-controlled, life-maintaining chemical reactions in all living organisms
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Metabolic pathway
A metabolic pathway is a series of chemical reactions occurring within a cell that are essential for survival. The product of the first reaction is used as the substrate for the next chemical reaction in the sequence
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Enzymes
Enzymes are hugely important to metabolism as they catalyze the reactions that must occur to keep the organisms alive. Enzymes are necessary because they allow these normally slow reactions to proceed quickly and efficiently
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The process, of several reactions occurring in order to make a final product, is referred to as a metabolic pathway. The final product can be anything - for example you eat some food (carbs, proteins or lipids) and there is a process they go through for the starch in carbs to be broken down into glucose, for protein molecules to be broken down to amino acids, for lipid molecules to be broken down into fatty acids and glycerol. It's not just one reaction to get from starch to glucose, there are a few - they are controlled by enzymes and are a metabolic pathway as the product from one reaction is the substrate for the next. |
Advantages of metabolic pathways 1. When the pathway is functioning, the initial substrates are continuously being converted into the intermediate substrate(s) and ultimately into the final product. Once there is a certain amount of final product, feedback mechanisms stop the pathway. This gives greater control over the reactions. This means that when there is enough of the final product, a signal is sent back to the first enzyme telling it to stop catalyzing the reactions because there is enough product. 2. Sophisticated reactions are possible due to metabolic pathways, which means that more complex molecules can be made. 3. Intermediate molecules/products (not the initial substrate, not the final product) can be used in other pathways. |
Enzymes are crucial to metabolic pathways!
Enzymes are needed to catalyze reactions and in a metabolic pathway there are several reactions to catalyze. Each reaction is different (they all use different substrates) which means one enzyme cannot catalyze all the reactions - because enzymes are specific - they have a particular shape and can only fit one type of substrate. This means our body needs to make several different enzymes for each metabolic pathway in our body. There are tonnes of metabolic pathways that allow our metabolism to function!
How are enzymes made? (you actually know this already!) - It's protein synthesis (transcription, RNA processing, translation). You have a genes that code for enzymes. The DNA on your gene is transformed into a message (mRNA) which is then sent out of the nucleus and to the ribosome where it is used to create a polypeptide chain (amino acids joined together) which then becomes a protein. Enzymes are made of proteins - so when a particular protein is made it becomes a particular enzyme. You have different genes for all the different enzymes you make!
How are enzymes made? (you actually know this already!) - It's protein synthesis (transcription, RNA processing, translation). You have a genes that code for enzymes. The DNA on your gene is transformed into a message (mRNA) which is then sent out of the nucleus and to the ribosome where it is used to create a polypeptide chain (amino acids joined together) which then becomes a protein. Enzymes are made of proteins - so when a particular protein is made it becomes a particular enzyme. You have different genes for all the different enzymes you make!
Mutations and Metabolic Pathways
Metabolic pathways hit trouble if there is a mutation.
A mutation in the DNA could change the enzyme made during protein synthesis -
if there is no enzyme to catalyze that particular reaction then it will not go ahead.
A mutation in the DNA could change the enzyme made during protein synthesis -
if there is no enzyme to catalyze that particular reaction then it will not go ahead.
This will lead to two things: 1. No end/final product 2. A build up of the substrate that the particular enzyme was supposed to turn into a product. Build-ups can often be very harmful to the individual |
Whether or not a mutation has an affect on the individual depends on whether the mutation occurs on a dominant or recessive allele
DOMINANT
If the mutated allele is dominant then only one copy of it needs to be inherited for the enzyme, and therefore the metabolic pathway, to be affected. Remember only one dominant allele needs to be present in the genotype for that trait to be shown in the phenotype
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RECESSIVE
If the mutated allele is recessive, the individual must inherit two copies of the allele before the function of the enzyme, and hence the metabolic pathway, is affected.
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Guinea pig coat colour (scipad page 212)
A and a
Gene A codes for enzyme A. Enzyme A has two alleles - A and a.
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B and b
Gene B codes for enzyme B. Enzyme B has two alleles - B and b.
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Remember everyone has 2 alleles for every gene;
this forms the genotype
this forms the genotype