PROTEINS

Proteins Proteins do the nitty-gritty jobs of every living cell. Proteins are made of long strings of individual building blocks known as amino acids.

Amino acids contain an amino group, a carboxyl group, a carbon and a unique R group

Identify amino acids ... from diagrams showing their structure. 3.2.2 Identify amino acids ... from diagrams showing their structure.

Polar R groups make the amino acid hydrophilic Non-polar R groups make the amino acid hydrophobic

Ionic R groups make the amino acid hydrophilic

Explain the significance of polar and non-polar amino acids. 7.5.3 Explain the significance of polar and non-polar amino acids.

There are 20 commonly occurring amino acids that are found in proteins leucine - leu - L lysine - lys - K methionine - met - M phenylalanine - phe - F proline - pro - P serine - ser - S threonine - thr - T tryptophan - trp - W tyrosine - tyr - Y valine - val - V alanine - ala - A arginine - arg - R *** asparagine - asn - N aspartic acid - asp - D cysteine - cys - C glutamine - gln - Q glutamic acid - glu - E glycine - gly - G histidine - his - H *** isoleucine - ile - I “Essential Amino Acids” are those that must be ingested in the diet (our body can’t make them)

Peptide Bonds join amino acids It’s a condensation reaction (meaning that H20 is released when the bond is formed). Two amino acids form a DI-PEPTIDE POLYPEPTIDES are formed from more than two amino acids bonded together

FIGURE 3-20 Protein synthesis In protein synthesis, a dehydration reaction joins the carbon of the carboxylic acid group of one amino acid to the nitrogen of the amino group of a second amino acid, releasing water. The resulting covalent bond between amino acids is called a peptide bond.

3.2.5 Outline the role of condensation and hydrolysis in the relationships between … amino acids and polypeptides. 7.4.5 Draw and label a diagram showing the structure of a peptide bond between two amino acids.

Proteins have four levels of organization

Primary structure is the amino acid sequence

The amino acid sequence is coded for by DNA and is unique for each kind of protein

The amino acid sequence determines how the polypeptide will fold into its 3D shape

mis-formed hemoglobin causes sickle cell disease Even a slight change in the amino acid sequence can cause the protein to malfunction For example, mis-formed hemoglobin causes sickle cell disease

Proteins have four levels of organization

Secondary structure results from hydrogen bonding between the oxygen of one amino acid and the hydrogen of another

FIGURE 3-22 The pleated sheet is an example of protein secondary structure In a pleated sheet, a single polypeptide chain is folded back upon itself repeatedly (connecting portions not shown). Adjacent segments of the folded polypeptide are linked by hydrogen bonds (dotted lines), creating a sheetlike configuration. The R groups (green) project alternately above and below the sheet. Despite its accordion-pleated appearance, produced by bonding patterns between adjacent amino acids, each peptide chain is in a fully extended state and cannot easily be stretched farther. For this reason, pleated sheet proteins such as silk are not elastic.

The alpha helix is a coiled secondary structure due to a hydrogen bond every fourth amino acid

The beta pleated sheet is formed by hydrogen bonds between parallel parts of the protein

A single polypeptide may have portions with both types of secondary structure Link to video

Proteins have four levels of organization

Tertiary structure depends on the interactions among the R group side chains

Types of interactions Hydrophobic interactions: amino acids with nonpolar side chains cluster in the core of the protein, out of contact with water = charged = hydrophobic

Types of interactions Hydrogen bonds between polar side chains

Types of interactions Ionic bonds between positively and negatively charged side chains

Types of interactions Disulfide bridge (strong covalent bonds) between sulfur atoms in the amino acid cysteine Link to video

FIGURE 3-23 Keratin structure

Proteins have four levels of organization

Quaternary structure results from interactions among separate polypeptide chains.

For example, hemoglobin is composed of 4 polypeptide chains Link to video

Proteins have four levels of organization

The folding of proteins is aided by other proteins, called chaperones Act as temporary braces as proteins fold into their final conformation Research into chaperones is a area of research in biology

FIGURE 3-21 The four levels of protein structure Levels of protein structure are represented here by hemoglobin, the oxygen-carrying protein in red blood cells (red discs represent the iron-containing heme group that binds oxygen). Levels of protein structure are generally determined by the amino acid sequence of the protein, interactions among the R groups of the amino acids, and interactions between the R groups and their surroundings.

7.5.1 Explain the four levels of protein structure, indicating the significance of each level.

Denaturation results in disruption of the secondary, tertiary, or quaternary structure of the protein

Denaturation may be due to changes in pH, temperature or various chemicals

Protein function is lost during denaturation, which is often irreversible

3.6.4 Define denaturation.

Folded proteins are placed into two general categories

Fibrous proteins have polypeptide chains organized in long fibers or sheets Water insoluble Very tough physically, may be stretchy

Functions of fibrous proteins Structural proteins function in support Insects and spiders use silk fibers to make cocoons and webs Collagen and elastin are used in animal tendons and ligaments Keratin is the protein in hairs, horns and feathers

Functions of fibrous proteins Contractile proteins function in movement Actin and myosin contract to create the cleavage furrow and to move muscles Contractile proteins move cilia and flagella

Globular proteins have their chains folded into compact, rounded shapes Easily water soluble

Functions of globular proteins Storage proteins function in the storage of amino acids Ovalbumin is the protein in egg whites Casein is the protein in milk, source of amino acids for baby mammals

Functions of globular proteins Transport proteins function in the movement of other substances Hemoglobin, the iron containing protein in blood, transport oxygen from lungs to other parts of the body (C3032H4816O872N780S9Fe4) Membrane transport proteins such as channels for potassium and water

Functions of globular proteins Hormone proteins function as cellular messenger molecules that help maintain homeostasis Insulin: sends message “allow sugar into cells” (when blood glucose levels are high, cells will transport glucose into the cells for use or storage) Glucagon: sends message “we need more sugar in the blood” (when blood glucose is too low, cells will release glucose)

Functions of globular proteins Receptor proteins allow cells to respond to chemical stimuli Growth factor receptors initiate the signal transduction pathway when a growth hormone attaches

Functions of globular proteins Cholesterol receptors on the cell membrane allow LDL to be endocytosed into the cell

Functions of globular proteins Protective proteins function as protection against disease Antibodies combat bacteria and viruses

Functions of globular proteins Enzymes speed up chemical reactions Amylase and other digestive enzymes hydrolyze polymers in food Catalase converts hydrogen peroxide H2O2 into water and oxygen gas during cellular respiration

Table 3-3 Functions of Proteins

Table 3-3 Functions of Proteins

Table 3-3 Functions of Proteins

Table 3-3 Functions of Proteins

Table 3-3 Functions of Proteins

Table 3-3 Functions of Proteins

7.5.2 Outline the difference between fibrous and globular proteins, with reference to two examples of each protein type. 7.5.4 State four functions of proteins, giving a named example of each.