Lecture 5 Flashcards
What are some of the functions of proteins?
- Associated with strength and muscle
- Wound healing
- Have a structural role and a functional role in cells
In what foods can protein be found?
Milk, eggs, legumes and many whole grains
Excess meat may result in high saturated fat intakes
Some proteins are working molecules. List them (6)
Enzymes
Antibodies
Transport vehicles
Hormones (not all are proteins – e.g., sex hormones made up of sterol (lipid)
Cellular “pumps” – what gets in and out of a cell
Oxygen carriers (e.g., hemoglobin)
Some proteins are for structure. In what (7)?
Tendons
Ligaments
Scars
Fibres of muscles
Cores of bone & teeth (collagen matrices – minerals cling onto making structures stronger)
Filaments of hair
Materials of nails
What is the structure of proteins? What are they made up of?
- Made of carbon, hydrogen, and oxygen (like fat and carbohydrates)
- Contain nitrogen
- Some amino acids also contain sulphur
Proteins are composed of amino acids. How can these make all the proteins?
The amino acids in a strand of protein are different from one another – not identical like starch
20 different amino acids make up most of the proteins of living tissue (A protein strand can contain 50 to 1000 amino acids. So many different combinations).
What is the structure of amino acids?
An amine group at one end - nitrogen-containing part
An acid group at the other end
A distinctive side chain (group) attached to the carbon at the center of the backbone which gives it its identity & chemical nature.
Must understand the structure of an amino acid. The “backbone” is the same for all amino acids. The side chain differs from one amino acid to the next. The nitrogen is in the amine group
What are some of the things side chains make the amino acids differ in?
Size, shape, electrical charge (Going to contribute to the shape and behaviours of the protein (repel, attract, neutral))
What does it mean for an amino acid to be essential or indispensible?
Cannot be synthesized at all by the body or cannot be synthesized in sufficient amounts
Can only be replenished from foods
The body cannot make the proteins it needs to do its work without the essential amino acids
The body can make the other amino acids from fragments derived from carbohydrate or fat to form the backbones & nitrogen from other sources
What does it mean for an amino acid to be nonessential or dispensible?
Amino acids that can be synthesized by the body
The body can make these from fragments derived from carbohydrate or fat to form the backbones
Nitrogen from other sources (e.g., dismantling amino acids)
What does it mean for an amino acid to be conditionally indispensible/essential?
An amino acid that is normally nonessential
in circumstances when the need exceeds that body’s ability to produce it, it must be supplied by the diet (e.g., tyrosine)
Describe what it means by “amino acids are recycled”
Body makes some amino acids but also breaks down proteins to reuse those amino acids:
- Food proteins (after digestion) & body proteins (after their cellular work) are dismantled freeing their amino acids
- Recycling system provides access to amino acids for energy when needed
Cells can use amino acids for energy if required. Like when?
Tissues can break down their own proteins in time of fuel or glucose deprivation
Working proteins are sacrificed
Priority system by the body to select tissue proteins to dismantle (most dispensable proteins used first and structural proteins of certain organs are guarded until their use is forced by dire need)
What is a peptide bond?
Connects one amino acid to another
Formed between the amine of one amino acid and the acid group of the next amino acid through a condensation reaction
Forms a chain of amino acids with side chains bristling out from the backbone
What is the primary structure?
The chain is the primary structure.
What is the secondary structure?
Determined by weak electrical attractions within the chain
Positively charged hydrogens attract nearby negatively charged oxygen
Sections of the chain may twist into a helix or fold into a pleated sheet giving proteins strength and stability
What is the tertiary structure?
Long polypeptide chains twist and fold into a variety of complex tangled shapes
Side groups may attract or repel each other
Side groups may be hydrophilic or hydrophobic (therefore the chain folds so hydrophilic side groups are on the surface near water & hydrophobic side groups are hidden in the middle)
Disulfide bridges also determine tertiary structure
Shape gives characteristics
What are quaternary structures?
Interactions between 2 or more polypeptides
Some polypeptides work together in large complexes
Some proteins strands function alone while other proteins are composed of several strands
What is hemoglobin?
A large globular protein that carries oxygen and is made up of four polypeptide chains
Proteins perform different tasks dictated by their shape, such as?
- Globular proteins are water soluble, such as some proteins of the blood
- Some proteins form hollow balls & carry/store materials in their interior
- Some proteins are much longer than they are wide like the proteins of tendons
What is collagen?
A protein from which connective tissues are made (tendons, ligaments, scars & the foundations of bones & teeth)
Acts like glue between cells
Elasticity in blood
What is insulin
As we know, it helps regulate blood sugar
Produced by the pancreas
Helps cells use sugar
What are enzymes?
Protein catalysts (facilitates a chemical reaction without being altered in the process)
What can be said about inherited amino acid sequences?
For each protein there exists a standard amino acid sequence
A sequence which is specified by heredity. Wrong amino acid can be disastrous to health (sickle cell anemia)
What is sickle cell disease?
Need to know it is the replacement of one amino acid to the other, altering the protein’s shape and its function (unable to carry oxygen efficiently), alters blood cells which can lead to blood clotting, strokes, and potentially early death.
Every human cell contains the DNA for making every human protein but cells do not contain every protein. How does the cell know to either express or suppress certain genes?
In general, cells monitor nutrient concentrations in the fluids surrounding them and triggers a cascade of molecular events inside the cell that ultimately leads to expression or suppression of certain genes
What are some examples of suppression or expression of certain genes?
Pancreas: Responds to internal molecular messages generated when blood glucose is overabundant by synthesizing insulin
Hemoglobin: When body’s iron stores run low, immature red blood cells respond by reducing hemoglobin synthesis. In contrast, abundant iron stimulates hemoglobin synthesis by immature red blood cells
What is the denaturation of protein, what causes it, and why is it important?
The irreversible change in a protein’s shape
Can be caused by heat (cooking), acids, bases and alcohols
Denaturation is important to the digestion of food protein (stomach acids open up a protein’s structure, allows digestive enzymes to make contact with the peptide bonds & cleave them).
Why are proteins digested?
Each protein performs a particular task in a specific tissue. Proteins eaten must be broken down and absorbed. Amino acids then are arranged into specific human body proteins.
How do some proteins digest others in the acidic stomach (pH of 2)?
Certain acid-tolerant proteins (many of which are enzymes), digest proteins from food that have been denatured by acid. The coating of mucus secreted by the stomach wall protects its proteins from attack by either acids or enzymes.
How is protein digested in the mouth?
Protein is crushed by chewing & moistened with saliva
Not really an enzymatic digestion happening yet
How is protein digested in the stomach?
Acid helps to uncoil the protein’s tangled strands so that the stomach’s protein-digesting enzyme can attack the peptide bonds.
Lining is protected from acid & enzymes by a mucus coating secreted by stomach cells
What is the stomach’s protein-digesting enzyme, which works best in an acidic environment?
Pepsin
It cleaves amino acid strands into polypeptides and a few amino acids.
How are proteins digested in the small intestine? What happens to proteins of different sizes?
Receives small denatured pieces of protein from the stomach (most are polypeptides, a few are single amino acids)
Alkaline juices from the pancreas neutralize the acid delivered by the stomach (pH increases to about 7 – neutral)
Cells lining the small intestine have enzymes on their surfaces that split most tri & dipeptides into single amino acids, which are then absorbed.
Some di & tripeptides are absorbed into cells where they are split into single amino acids before being released into the bloodstream
A few larger peptide molecules can escape the digestive process altogether and enter the bloodstream intact
What are the protein-digesting enzymes from the pancreas & small-inestine and what do they do?
Proteases
Continue breaking down protein until nearly all that is left are dipeptides, tripeptides, or single amino acids
Does taking enzyme help?
No. Even the stomach’s digestive enzymes are denatured and absorbed when their jobs are through as amino acids.
Do predigested proteins (amino acid supplements) help protect the digestive system from overworking?
No. The healthy digestive system easily handles whole proteins
Single amino acid supplements may compete for absorption sites or overwhelm a carrier resulting in possible deficiency in another amino acid
What happens to amino acids in the bloodstream? Where are they taken (2)?
Carried to the liver
Used by the liver or released into the blood to be taken up by other cells
What happens when amino acids are for the liver?
Used in protein synthesis, used for energy, or used to synthesize a nonessential amino acid and released into bloodstream for cells
What happens when amino acids are used by the cells?
Use the amino acids to make proteins for their own use, make proteins that are released into the lymph or blood for other uses. When necessary, body cells can use amino acids for energy
What are the roles of protein in the body (6)?
- Supporting growth and maintenance
- Building enzymes, hormones, and other compounds (amino acids & antibodies)
- Maintaining fluid and electrolyte balance
- Maintaining acid-base balance
- Clotting of blood
- Providing energy and glucose (when insufficient carb and fat)
The continuous breakdown & synthesis of body proteins involving the recycling of amino acids is what? And how many grams per day?
Protein turnover (300-400g/day)
Amino acids are not only building blocks for protein. Which ones are examples of this?
Tyrosine is a component of both epinephrine and norepinephrine and is used to make both melanin and thyroxine
Tryptophan serves as a starting material for serotonin and niacin