Proteins Flashcards
What are proteins?
Proteins are polymers and macromolecules made of monomers called amino acids. The sequence, type, and number of amino acids within a protein determine its shape and function. Proteins are extremely important in cells, forming enzymes, cell membrane proteins, hormones, immunoproteins, transport proteins, structural proteins, and contractile proteins.
Why are proteins crucial for life processes?
They are coded for by our genes and form the basis of living tissues. They also play a central role in biological processes. For example, proteins catalyse reactions in our bodies, transport molecules such as oxygen, keep us healthy as part of the immune system and transmit messages from cell to cell.
What are amino acids?
Amino acids are the monomers of polypeptides. There are 20 amino acids found in polypeptides common to all living organisms. Their general structure consists of a central carbon atom (alpha carbon) bonded to an amine group (-NH2), a carboxylic acid group (-COOH), a hydrogen atom, and an R group, which varies between different amino acids.
How does the R group affect amino acid properties?
The R group is responsible for the differences between amino acids and their properties. It determines whether an amino acid is acidic or basic, and whether it is polar or non-polar. The R group can range from a simple hydrogen atom (in glycine) to complex aromatic ring structures (e.g., in phenylalanine).
What is a peptide bond?
A peptide bond is formed when the carboxyl group (-COOH) of one amino acid bonds with the amine group (-NH2) of another amino acid, releasing a water molecule in a condensation reaction. This bond connects amino acids to form peptides and proteins.
How is a dipeptide formed?
A dipeptide is formed by the condensation of two amino acids. During this process, a hydroxyl group (-OH) is lost from the carboxylic group (-COOH) of one amino acid, and a hydrogen atom is lost from the amine group (-NH2) of another amino acid. The remaining parts bond together, releasing a water molecule.
What is the difference between a polypeptide and a dipeptide?
A dipeptide is formed by the condensation of two amino acids, while a polypeptide is formed by the condensation of many (3 or more) amino acids. Polypeptides are longer chains of amino acids connected by peptide bonds.
How are proteins broken down into amino acids?
Proteins are broken down into amino acids through hydrolysis reactions. During hydrolysis, water is added to break the peptide bonds, reversing the condensation reaction that formed the polypeptide. This process is essential for digestion and cellular metabolism.
What are essential amino acids?
Essential amino acids are the nine amino acids that our bodies cannot synthesize and must be obtained through our diet. A healthy, varied, well-balanced diet will contain all nine essential amino acids required for proper protein synthesis and cellular function.
What are non-essential amino acids?
Non-essential amino acids are the 11 amino acids that our cells can synthesize from other amino acids. Unlike essential amino acids, these do not need to be obtained directly from the diet as the body can produce them.
Why is a varied diet important for vegetarians and vegans?
A varied diet is important for vegetarians and vegans to ensure they consume all nine essential amino acids regularly. While meat contains all nine essential amino acids, plant-based diets need to be well-balanced and varied to provide all the necessary amino acids for proper protein synthesis and cellular function.
How does the genetic code relate to protein diversity?
The genetic code, or DNA base sequence, determines the number and order of amino acids in a polypeptide. The vast variety of possible DNA base sequences allows for an almost infinite number of potential polypeptide combinations, contributing to the large diversity of proteins available to living organisms.
How are polypeptides assembled in cells?
Polypeptides are assembled at ribosomes by condensing individual amino acids onto a growing chain, one by one. The mRNA codon determines which amino acid is added at each step, allowing for a choice of 20 amino acids each time one is added to the chain.
What factors contribute to the variety of proteins in living organisms?
The variety of proteins in living organisms is due to several factors: the 20 naturally occurring amino acids that form the basic structure of polypeptide chains, the variation in polypeptide length (from a few to thousands of amino acids), and the diversity in structure and amino acid sequence determined by the genetic code.
What is the role of enzymes in cellular reactions?
Enzymes, which are proteins, speed up cellular reactions through catalysis. They play a crucial role in various metabolic processes by lowering the activation energy required for chemical reactions to occur, thereby increasing the rate of these reactions in cells.
How do proteins contribute to blood clotting?
Proteins contribute to blood clotting by interacting with oxygen to form a gel-like scab across a wound. This process involves a cascade of protein interactions that ultimately lead to the formation of a fibrin clot, which helps stop bleeding and protect the wound.
What are some examples of structural proteins?
Examples of structural proteins include collagen and keratin. These proteins form strengthening fibers in skin, hair, tendons, and blood vessels, providing structural support and protection to various tissues in the body.
How do transport proteins function in the body?
Transport proteins, such as hemoglobin, function by carrying vital metabolites throughout the body. Hemoglobin, for example, transports oxygen in the blood, allowing for efficient delivery of oxygen to tissues and organs.
What is the role of proteins in the cytoskeleton?
Proteins form the cytoskeleton, a network of tubules within a cell that causes chromosomes to move during the cell cycle. The cytoskeleton provides structural support to the cell, helps maintain cell shape, and plays a crucial role in cell division and intracellular transport.
How do proteins contribute to cell adhesion?
Proteins contribute to cell adhesion by allowing cells in the same tissue to stick together. Cell adhesion proteins, such as cadherins and integrins, form connections between adjacent cells or between cells and the extracellular matrix, helping to maintain tissue integrity and structure.
What is the role of proteins in hormone function?
Some proteins function as hormones, which are chemical messengers secreted in one part of the body to have an effect elsewhere. Protein hormones, such as insulin and growth hormone, play crucial roles in regulating various physiological processes in the body.
How do histone proteins contribute to DNA storage?
Histone proteins contribute to DNA storage by facilitating the compaction of DNA in chromosomes. They act as spools around which DNA winds, allowing for efficient packaging of genetic material within the nucleus of cells.
What is the role of antibodies in the immune response?
Antibodies, also known as immunoglobulins, are proteins produced by the immune system to recognize and neutralize foreign substances such as pathogens. They are the most diverse group of proteins and play a crucial role in the body’s defense against infections and diseases.
How do membrane transport proteins function?
Membrane transport proteins, such as channel and carrier proteins, determine which substances can pass across cell membranes. They facilitate the movement of specific molecules or ions across the lipid bilayer, either through passive diffusion or active transport mechanisms.
What is the function of cell receptor proteins?
Cell receptor proteins act as binding sites for various stimuli, including hormones, chemical signals (such as tastes), light, and sound. They play a crucial role in cell signaling and communication by detecting external signals and initiating appropriate cellular responses.
What is Rubisco and why is it important?
Rubisco (Ribulose Bisphosphate Carboxylase) is an enzyme that catalyzes the fixing of CO2 from the atmosphere during photosynthesis. It is composed of 16 polypeptide chains as a globular protein and is considered the most abundant enzyme on Earth. Rubisco is crucial as it is the source of all organic carbon, making it arguably the most important enzyme in nature.
What is the structure and function of insulin?
Insulin is a hormone produced and secreted by β-cells in the pancreas. It is composed of two polypeptide chains and functions as a short, globular protein. Insulin binds reversibly to insulin receptors on liver, fat, and muscle cells, causing the absorption of glucose from the blood.
What are immunoglobulins and how do they function?
Immunoglobulins, also known as antibodies, are Y-shaped globular proteins with specific binding sites at the two tips of the ‘Y’. They bind to specific antigens and are highly variable, allowing for the production of antibodies against millions of different antigens. Immunoglobulins are the most diverse range of proteins.
What is rhodopsin and what is its role in vision?
Rhodopsin is a pigment in the retina of the eye, expressed in rod cells. It is a membrane protein containing a light-sensitive part called retinal, derived from Vitamin A. When a photon of light hits rhodopsin, it causes a conformational change, sending a nerve impulse along the optic nerve to the central nervous system, thus playing a crucial role in vision.
What are the characteristics and functions of collagen?
Collagen is a fibrous protein made of three separate polypeptide chains. It is the most abundant protein in the human body, making up approximately 25% of total protein content. Collagen forms a network in skin, blood vessel walls, and connective tissue that can resist tearing forces. It also plays a role in teeth and bones, helping to reduce their brittleness.
What are the unique properties of spider silk protein?
Spider silk protein is as strong as steel wire but considerably lighter. It contains rope-like, fibrous parts and coiled parts that stretch under tension, allowing for extension and resistance to breaking. Spider silk does not denature easily at extreme temperatures and has attractive aspects for engineering and textile product design due to its strength and low weight.
How does protein denaturation occur?
Protein denaturation occurs when the environment of a protein changes, particularly due to temperature and pH extremes. These changes interfere with the ionic interactions, hydrogen bonds, and other intermolecular forces between polypeptide chains, causing an irreversible change in the protein’s conformation. This altered shape may affect the protein’s function, physical state, and general usefulness in its original role.
Why are the bonds between R groups important for protein structure?
The bonds that form between different R groups are relatively weak compared to the peptide bonds that hold the amino acids in sequence. These weaker bonds can be broken easily, which can cause the conformation of the protein to change and lead to denaturation. The integrity of these bonds is crucial for maintaining the protein’s 3D structure and function.
What is the relationship between pH and protein structure?
A certain pH is considered optimal for a particular protein because at that pH, the protein’s 3D structure is not denatured. Changes in pH can affect the ionic interactions and hydrogen bonds that maintain the protein’s structure, potentially leading to denaturation. Some proteins can undergo small denaturations and renaturations in response to small fluctuations in pH, such as hemoglobin.
How does heat affect protein structure?
Heat can cause protein denaturation by breaking the weak bonds that maintain the protein’s 3D structure. As temperature increases, the increased kinetic energy of the molecules can disrupt hydrogen bonds and other weak interactions, causing the protein to unfold or change its conformation. This can lead to a loss of function in enzymes and other proteins.
What happens to egg white protein during cooking?
When egg white (mainly the protein albumin) is cooked, denaturation occurs. The heat causes the hydrophobic amino acids, normally at the center of the albumin molecule, to appear at the edges. This makes the protein insoluble, forming a harder, solid layer. Similar events occur in the proteins of the egg yolk as it cooks.
How does stomach acid affect dietary proteins?
The low pH (around 2) in the stomach causes proteins in the diet to become denatured. This denaturation is part of the digestive process, as it helps to unfold the proteins, making them more accessible to digestive enzymes like pepsin. Pepsin, a protein-digesting enzyme, has an optimum pH of 2 for this reason.
What are extremophiles and how do they relate to protein stability?
Extremophiles are organisms that have evolved to live in extreme environments. They have proteins that are stable even at extreme pH or temperature. For example, Thermus aquaticus is a bacteria that lives in hot springs at 80°C, a temperature that would denature most other proteins. The proteins of extremophiles have adapted to function under these extreme conditions.
How is enzyme denaturation used in experiments?
Denaturation of enzymes can be used as part of experiments to measure enzyme activity. For example, experiments to establish the optimum pH or temperature of an enzyme (e.g., pepsin or lipase) often involve exposing the enzyme to various conditions and observing changes in its activity. The point at which activity decreases sharply often indicates the onset of denaturation.
Why can’t many protein-based drugs be taken orally?
Many drugs that are proteins cannot be taken by mouth because the protein will be denatured by stomach acid. The low pH in the stomach would cause these protein drugs to lose their structure and function. Therefore, these drugs need to be delivered in another way, such as by direct injection into the blood, to maintain their effectiveness.
How many amino acids are commonly found in proteins?
While around 500 amino acids have been found in nature, only 20 are commonly found in proteins. These 20 amino acids are the building blocks for most proteins found on Earth.
What is the difference between essential and non-essential amino acids in humans?
Of the 20 common amino acids, eleven can be naturally synthesized within human cells. These are called non-essential amino acids. The other nine amino acids are essential, meaning they must be obtained through the human diet as our bodies cannot produce them.
Why is there so much chemical diversity among amino acids?
The chemical diversity among amino acids is due to the variation in their R groups. Because the R groups vary so much between the 20 amino acids, there is a lot of chemical diversity, which contributes to the wide range of protein structures and functions.
What are the components of an amino acid’s structure?
An amino acid’s structure consists of a central carbon atom (the alpha carbon) bonded to an amine group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and an R group. The R group is what distinguishes one amino acid from another.
How do amino acids behave in a neutral environment?
In a neutral environment, amino acids ionize. The carboxyl group donates a hydrogen ion while the amine group accepts it, resulting in the carboxyl group having a negative charge and the amine group having a positive charge.
What are the two main categories of R-groups in amino acids?
R-groups in amino acids can be categorized as either hydrophobic or hydrophilic. Hydrophilic R-groups are polar and can be either acidic or basic, while hydrophobic R-groups are non-polar.
How does the structure of proteins relate to their function?
The structure of proteins is directly related to their function. The sequence, type, and number of amino acids within a protein determine its shape, which in turn determines its function. The precise folding and 3D structure of a protein are crucial for its specific role in biological processes.
What are the four levels of protein structure?
The four levels of protein structure are primary, secondary, tertiary, and quaternary. The primary structure is the sequence of amino acids. The secondary structure involves local folding patterns like alpha helices and beta sheets. The tertiary structure is the overall 3D shape of a single polypeptide chain. The quaternary structure involves the interaction of multiple polypeptide chains.
What is the primary structure of a protein?
The primary structure of a protein is the linear sequence of amino acids in the polypeptide chain. This sequence is determined by the genetic code and forms the foundation for the higher levels of protein structure.
