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Cell Biology: Cell Compounds and Biological Molecules. Lesson 4 – Proteins and Nucleic Acids ( Inquiry into Life pg. 37-41 ). Today’s Objectives. Analyze the structure and function of biological molecules in living systems, including carbohydrates, lipids, proteins, nucleic acids
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Cell Biology:Cell Compounds and Biological Molecules Lesson 4 – Proteins and Nucleic Acids (Inquiry into Life pg. 37-41)
Today’s Objectives • Analyze the structure and function of biological molecules in living systems, including carbohydrates, lipids, proteins, nucleic acids • List the major functions of proteins • Draw a generalized amino acid and identify the amine, acid (carboxyl), and R-groups • Identify the peptide bonds in dipeptides and polypeptides • Differentiate among the different levels of protein organization with respect to structure and bond type, including: primary, secondary, tertiary, quaternary • Name the four bases in DNA and describe the structure of DNA using the following terms: nucleotide (sugar, phosphate, base), complementary base pairing, double helix, hydrogen bonding • Relate the general structure of the ATP molecule and its role as “energy currency”
2.7 - Proteins • Proteins have many functions: • Proteins such as keratin and collagen have structural roles. • Proteins are also enzymes that speed up the chemical reactions of metabolism. • Proteins such as hemoglobin are responsible for the transport of substances within the body. • Proteins transport substances across cell membranes. • Proteins form the antibodies of the immune system that defend the body from viruses and disease. • Proteins such as insulin are hormones that regulate cellular function. • Contractile proteins such as actin and myosin allow parts of cells to move and muscles to contract.
What are proteins? • Contain carbon, hydrogen, oxygen, and nitrogen • Also often contain sulfur, and sometimes phosphorus and iron • The basic structure of a protein is a chain of amino acids (polypeptides) • There are about 20 different amino acids
What are amino acids? • Proteins are polymers with amino acid monomers • An amino acid has a central carbon atom bonded to a hydrogen atom and three groups: • One of the three groups is an amino group (-NH2), • One of the groups is an acidic group (-COOH) • Hence called an amino acid! • The third group is called an R Group • Amino acids differ from one another by their R group
What are R groups? • An R group is a variety of atoms attached to amino acids • R group = radical group or remainder group • An R group distinguishes one amino acid from another
Formation of Proteins • An amino acid can be referred to as a peptide • Dehydration synthesis of amino acids result in the bonding of amino acids together and the release of water molecules • When two amino acids bond together, they produce a dipeptide • Example: amino acids glycine and alanine bond to form the dipeptide gly-ala
Formation of proteins • The bond that connects amino acids is called a peptide bond • A dipeptide has one peptide bond holding together two amino acids • A Tripeptidewould have two peptide bonds holding together three amino acids • A polypeptide would have numerous peptide bonds holding together numerous amino acids • A polypeptide is a single chain of amino acids • The order or combination of these amino acids determines which protein is produced
Formation of proteins • This process when repeated form long sequences of amino acids, or proteins • These sequences take on specific features and characteristics of the individual amino acids that are bonded together
Protein Structure • There are three to four levels of protein structure • Primary structure – sequence of amino acids (polypeptide) • Secondary structure – orientation of polypeptide • Tertiary structure – final 3-D shape of polypeptide • Quaternary structure* - arrangement of multiple polypeptides • *not all proteins have multiple polypeptides
Primary Structure • Simply the sequence of amino acids • Because there are twenty amino acids, it is easy to see that there are literally millions of different possible amino acid sequences • Consequently, there are millions of proteins
Secondary Structure • As the amino acid chains (polypeptides) get longer, they begin to twist or fold • This is a result of stress on the peptide bonds • Two types of secondary structure: • Alpha helix – like a spiral • Beta pleated sheet – like folded paper • The alpha helix is most common
Secondary Structure – alpha helix • As the polypeptide bends into a spiral, hydrogen bonds form between the hydrogen of one amino acid and an oxygen further down the chain • This hydrogen bond helps the alpha helix hold its shape • An alpha helix contains 3.6 amino acids per spiral
Secondary Structure – Beta pleated sheet • Hydrogen bonds can form between parallel lengths of the polypeptide chain creating beta pleated sheets
Tertiary Structure • The third level of protein structure or tertiary structure is described as the bending and folding of the alpha helix • As the helix gets longer there are some amino acids that cannot fit the configuration and therefore cause kinks • New bonds will form to hold it into a three dimensional (3-D) shape • These bonds can be ionic, covalent, and/or hydrogen bonds
Tertiary Structure Alpha helix
Quaternary Structure • Only occurs in proteins with more than one polypeptide • The quaternary structure is where different 3-D (tertiary) configurations are associated with and function with each other • Imagine multiple kinked helixes tied up with each other in knots • An example of a protein with quaternary structure is hemoglobin which transports substances through our body in our blood
More about Protein Functions • Enzyme proteins speed up chemical reactions in our body • Reactions that normally would take several hours will take only a fraction of a second • Proteins such as hemoglobin transport nutrients and other substances through our body • Antibody proteins fight infections and attack viruses • The protein keratin is the main structural component of fingernails and hair • Collagen makes up the connective tissues in our muscles • Actin/myosin make up muscle fibers that allow for movement
2.8 Nucleic Acids • Nucleic Acids are polymers made up of monomers called nucleotides • There are two types of nucleic acids: • DNA – deoxyribonucleic acid • RNA – ribonucleic acid • Some functions of Nucleic Acids: • They form genetic material and are involved in the functioning of chromosomes and protein synthesis • DNA stores genetic information • DNA codes for the order of amino acids in a protein • RNA is an intermediary in the sequencing of amino acids into a protein
What are Nucleotides? • Nucleotides are made from a pentose sugar, a phosphate group, and a nitrogen containing base
Nucleotides • There are five basic nucleotides: • Adenine and Guanine • Double ring structure purines • Cytosine, Uracil, and Thymine • single ring structure pyrimidines • These bases are found in DNA and RNA • DNA contains A,G,T and C • RNA contains A,G,U and C
Nucleotides • The bases found in DNA form complementary base pairs (the same two bases always bond with each other) • The structure of DNA is a double helix (we will talk more about DNA later this year
ATP (Adenosine Triphosphate) • One particularly important nucleic acid is the modified nucleotide known as ATP • ATP is an RNA nucleotide with an adenine (A) base (adenine + ribose = adenosine) attached to 3 phosphate groups • ATP is a very high energy molecule • When ATP undergoes hydrolysis, large amounts of energy are released
ATP: The energy currency of cells • ATP is a high energy molecule because the last two phosphate bonds are unstable and easily broken • A lot of energy is required to maintain these bonds • If the bonds are broken, this energy is released • When an ATP molecule loses a phosphate, it becomes the molecule ADP (adenosine diphosphate) and a phosphate molecule • With the addition of energy, this process can be reversed, creating the ATP cycle • Muscle cells use the energy for muscle contraction • Cells use the energy to synthesize carbohydrates and proteins • More on this later in the year
Pop Quiz! • An amino acid is a central hydrogen atom attached to a hydrogen atom and what? • What are the monomers called that make up proteins? • Describe primary protein structure • Describe secondary protein structure • What are the two main types of secondary structure • Describe tertiary protein structure • Describe quaternary protein structure • What are 3 main functions of proteins? • What are the monomers called that make up nucleic acids? • How do cells get energy from the hydrolysis of ATP? • What are the 4 bases found in DNA?