Flashcards
Proteins and Enzymes: Structure and Function
Which type of bond joins amino acids one after another into a protein chain?
peptide bond
ester bond
hydrogen bond
glycosidic bond
True or false?
Proteins in the human body are built from 20 standard amino acids.
True or false?
Glycine, the smallest amino acid, has just a hydrogen atom as its side chain.
True or false?
Amino acids differ from one another only in their side chain, also called the R group.
True or false?
The human body can make all 20 amino acids itself, so none of them must come from food.
Digestive enzymes break the proteins in food down into single amino acids. Which molecule is used up each time one bond between two amino acids is broken?
oxygen
water
ATP
carbon dioxide
A protein chain is made of 50 amino acids. How many bonds join one amino acid to the next along this chain?
49
Match each example with the level of protein structure it describes.
primary structure
Human and pig insulin differ by just one amino acid in their sequence.
Match each example with the level of protein structure it describes.
secondary structure
Stretches of a keratin chain in hair coil into spring-like helices held by hydrogen bonds.
Match each example with the level of protein structure it describes.
tertiary structure
A lysozyme chain folds into a compact ball, held in shape partly by four disulfide bridges.
The picture shows hemoglobin: four folded chains, two alpha and two beta, fitted together into one protein. Which of these proteins are also built from several chains like this?
antibody (IgG)
myoglobin
catalase
pepsin
Match each protein with the job it does in the body.
insulin
tells body cells to take up glucose from the blood
Match each protein with the job it does in the body.
collagen
makes tendons and skin strong and tough
Match each protein with the job it does in the body.
myosin
pulls on actin filaments so muscles contract
Match each protein with the job it does in the body.
antibodies
bind to viruses and bacteria and mark them for destruction
True or false?
The order of amino acids in a protein is coded by a gene in the cell's DNA.
True or false?
Proteins contain nitrogen, which typical carbohydrates and fats do not.
True or false?
The body stores extra amino acids for later, the same way it stores extra fat.
True or false?
A protein's function depends only on which amino acids it contains, not on its shape.
True or false?
An enzyme molecule is used up after it speeds up one reaction.
True or false?
Enzymes speed up reactions by lowering the activation energy needed to start them.
True or false?
Most enzymes are proteins, but some RNA molecules can also act as catalysts.
True or false?
Enzymes make reactions possible that could never happen on their own.
Catalase in your liver breaks down harmful hydrogen peroxide into water and oxygen. Match each part of this reaction with its role.
catalase
enzyme
Catalase in your liver breaks down harmful hydrogen peroxide into water and oxygen. Match each part of this reaction with its role.
hydrogen peroxide
substrate
Catalase in your liver breaks down harmful hydrogen peroxide into water and oxygen. Match each part of this reaction with its role.
water and oxygen
products
Catalase in your liver breaks down harmful hydrogen peroxide into water and oxygen. Match each part of this reaction with its role.
the pocket on catalase where hydrogen peroxide binds
active site
Amylase in saliva breaks down starch but has no effect on the proteins in the same bite of food. Why?
Cooking already breaks proteins down into amino acids.
Amylase is used up on the starch before it can reach the proteins.
Only starch has the right shape to fit amylase's active site.
Proteins are too large to be broken down by any enzyme.
Only starch has the right shape to fit amylase's active site.
According to the induced fit model, what happens when a substrate binds to an enzyme?
The active site stays rigid and matches the substrate exactly, like a key in a lock.
The active site changes shape slightly to fit tightly around the substrate.
The enzyme breaks apart into subunits that surround the substrate.
The substrate permanently changes the order of amino acids in the enzyme.
The active site changes shape slightly to fit tightly around the substrate.
Fill in the gaps.
Pepsin, made in the
. . . . . , works best at about pH
. . . . . , while trypsin, made in the
. . . . . , works best at about pH
. . . . . .
Pepsin, made in the stomach , works best at about pH 2 , while trypsin, made in the pancreas , works best at about pH 8 .
True or false?
A competitive inhibitor fits into the active site and blocks the substrate from binding.
True or false?
Adding a lot more substrate can weaken the effect of a competitive inhibitor.
True or false?
A noncompetitive inhibitor works by binding to the substrate instead of the enzyme.
True or false?
Aspirin relieves pain by blocking an enzyme the body uses to make inflammation signals.
A gelatin dessert made with fresh pineapple never sets, but one made with canned pineapple sets normally. Why?
Canning adds sugar, which helps gelatin molecules link together.
Canning removes the fruit's acid, which would stop gelatin from setting.
Canned fruit holds less water, so it does not dilute the gelatin.
Canning heats the fruit, which destroys an enzyme that breaks down gelatin.
Canning heats the fruit, which destroys an enzyme that breaks down gelatin.
True or false?
Frying an egg denatures proteins in the egg white, which is why it turns white and firm.
True or false?
Denaturation breaks the peptide bonds, so the protein falls apart into single amino acids.
True or false?
Stomach acid denatures proteins in food, which makes them easier for enzymes to digest.
True or false?
A boiled egg white turns clear and runny again once it cools down.