Proteins (Edexcel International A Level (IAL) Biology): Flashcards

The tertiary structure of a protein is maintained by hydrogen bonds, disulphide bonds, ionic bonds and hydrophobic interactions between the R groups of amino acids.

True.

Quaternary structure is present in proteins that have more than one polypeptide chain, such as haemoglobin.

A biological catalyst is a substance found in living organisms that speeds up the rate of chemical reactions without being used up or permanently changed itself.

An anabolic reaction builds up new molecules, while a catabolic reaction breaks down large, complex molecules into smaller, simpler ones.

Enzymes have a unique active site where specific substrates bind, forming an enzyme-substrate complex.

False.

Enzymes are highly specific because their active site has a specific shape that only fits one particular substrate, determined by its tertiary structure.

An intracellular enzyme is produced and functions inside the cell where it was made.

An extracellular enzyme is secreted by a cell and catalyses reactions outside the cell, such as digestive enzymes in the gut.

If the tertiary structure of an enzyme is altered, the active site will change and the substrate will no longer fit.

Enzymes speed up chemical reactions by lowering the activation energy needed by forming an enzyme-substrate complex, making it easier for reactions to occur at normal temperatures and pressures.

Enzymes are catalysts because they speed up reactions without being used up or permanently changed.

The lock-and-key hypothesis is a model of enzyme activity that proposes the active site and substrate are rigid and fit together very precisely, like a key fits into a lock.

The induced-fit hypothesis is a model of enzyme activity that states the enzyme and substrate can change shape slightly when they interact, allowing for an ideal binding arrangement and efficient catalysis.

Extremes of heat or pH can alter the enzyme's structure and change the shape of its active site, resulting in denaturation and loss of function.

The optimum temperature is the temperature at which an enzyme catalyses a reaction at its maximum rate.

At temperatures above the optimum, enzyme activity drops sharply as the enzyme begins to denature, causing permanent changes to the active site and preventing substrate binding.

As temperature increases, molecules move more quickly, leading to a higher frequency of successful collisions between enzyme and substrate.

False.

At low temperatures, reactions slow down or stop because molecules move slowly, not because the enzyme is denatured.

Denaturation is the irreversible change to an enzyme's tertiary structure, usually due to high temperature or extreme pH, that alters the active site and prevents substrate binding.

pH affects enzyme activity by altering the hydrogen and ionic bonds that maintain the enzyme's shape. Extreme pH levels can denature the enzyme, changing its active site and reducing or stopping activity.

The enzyme pepsin is found in the stomach and has an optimum pH of 2.

Buffer solutions are used to maintain a constant pH during enzyme experiments, ensuring that the pH does not change as the reaction proceeds.

The saturation point is when all active sites of the enzyme are occupied, so increasing substrate concentration no longer increases the reaction rate.

If the amount of substrate is limited, increasing enzyme concentration will not increase the rate of reaction because the substrate becomes a limiting factor.

You can calculate the initial rate by drawing a tangent through the origin on the graph of product or substrate versus time, and measuring the gradient of the tangent.

False.

Once all enzyme active sites are occupied (saturation point), further increases in substrate concentration do not increase the rate of reaction.

During an experiment to investigate enzyme concentration, the volume of oxygen produced will increase as the enzyme concentration increases, but will plateau out once the substrate becomes limiting.

A nucleotide is the basic building block of nucleic acids, consisting of a pentose sugar, a phosphate group, and a nitrogenous base.

Nucleotides in a polynucleotide chain are linked together by phosphodiester bonds.

In DNA, the base adenine always pairs with thymine, and guanine always pairs with cytosine.

Complementary base pairing refers to the specific pairing of adenine with thymine and guanine with cytosine in DNA through hydrogen bonds.

DNA nucleotides contain deoxyribose sugar, while RNA nucleotides contain ribose sugar.

The sugar-phosphate backbone is the repeating chain of sugars and phosphate groups in a polynucleotide, linked by phosphodiester bonds.

A purine base has a double ring structure, while a pyrimidine base has a single ring structure.

True.

DNA strands are held together by hydrogen bonds between complementary bases.

RNA molecules are usually single stranded, whereas DNA molecules are usually double stranded.

The nitrogenous base uracil is found in RNA but not in DNA.

DNA strands are antiparallel, meaning they run in opposite directions: one from 5’ to 3’ and the other from 3’ to 5’.

DNA is usually a double-stranded polynucleotide with deoxyribose sugar, while RNA is usually single-stranded and contains ribose sugar.

The three-dimensional structure of DNA is called a double helix.

True.

A condensation reaction between two nucleotides forms a phosphodiester bond.