Understanding Proteins and Their Functions in Cellular Activities

1. CHAPTER 3The Molecules of Cells Modules 3.11 – 3.20

2. PROTEINS 3.11 Proteins are essential to the structures and activities of life • Proteins are involved in • cellular structure • movement • defense • transport • communication • Mammalian hair is composed of structural proteins • Enzymes regulate chemical reactions Figure 3.11

3. Two gene pairs-Four gene pairs?? • Phaeomelanin colors hair red. • Nored/red • Eumelanin- determines the darkness of the hair color. • Low brown eumelanin results in blonde hair • Higher brown eumelanin results in brown. • Brown/blonde • High black eumelanin results in black hair • Low black eumelanin results in gray hair • Black/grey • Most noticeable in red-heads, all humans have varying concentrations of phaeomelanin. Hair color -eumelanin and phaeomelanin

4. Brown/blonde Not Red/red • Phaeomelanin is more chemically stable than black eumelanin. But less chemically stable than brown eumelanin. So it breaks down more slowly when oxidized. Brown-Red-Black (most stable to least stable) • Bleach will cause darker hair to turn reddish-brown during the artificial coloring process. As the phaeomelanin continues to break down, the hair will gradually become orange, later yellow, and then white.

5. Muscle contraction –actin and myosin http://www.sci.sdsu.edu/movies/actin_myosin.html

6. Enzymes - proteins that catalyze chemical and biochemical reactions within living cell and outside. This group of proteins probably is the biggest and most important group of the proteins. • Hormones - proteins that are responsible for the regulation of many processes in organisms. Hormones are usually quite small and can be classifies as peptides (2-100 aa.) Best known protein hormones are: insulin, growth factors, etc. • Transport proteins - These proteins are transporting or store some other chemical compounds and ions. Some of them are well known: cytochrome C - electron transport; hemoglobin and myoglobin - oxygen transport • Immunoglobulin or Antibodies - proteins that involved into immune response of the organism to neutralize large foreign molecules, which can be a part of an infection. ie. antibodies • Structural proteins - These proteins maintain the structure of other biological components, like cells and tissues. Collagen, elastin, α-keratin, fibrin - these proteins are involved into formation of the whole organism body. • Motor proteins. These proteins can convert chemical energy into mechanical energy. actin and myosin are responsible for muscular motion. • Receptors These proteins are responsible for signal detection and translation into other type of signal. • Signalling proteins - This group of proteins is involved into signaling transduction process. • Storage proteins. These proteins contain energy, which can be released during metabolism processes in the organism. Egg ovalbumin and milk casein are such proteins.

7. 3.12 Proteins are made from just 20 kinds of amino acids • Proteins are the most structurally and functionally diverse of life’s molecules • Their diversity is based on different arrangements of amino acids • Proteins may be composed of one polypeptide chain or several. • Protein folding of the chain is essential to protein function.

8. an amino group • a carboxyl group • an R group, which distinguishes each of the 20 different amino acids • The monomer of a polypeptide is an amino acid. Each amino acid contains: Aminogroup Carboxyl (acid)group Figure 3.12A

9. Each amino acid has specific properties Leucine (Leu) Serine (Ser) Cysteine (Cys) HYDROPHOBIC HYDROPHILIC Figure 3.12B

10. (*) Essential only in certain cases. 20 amino acids • An essential amino acid is an amino acid that cannot be synthesized de novo by the organism (usually referring to humans), and therefore must be supplied in the diet. • Eight amino acids are generally regarded as essential for humans: phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, leucine, and lysine • PVT. TIM HALL (histidine and arginine in children )

11. Amino acids can be linked by peptide bonds to form polypeptides. • Cells link amino acids together by dehydration synthesis • The bonds between amino acid monomers are called peptide bonds Carboxylgroup Aminogroup PEPTIDEBOND Dehydrationsynthesis Amino acid Amino acid Dipeptide Figure 3.13

12. 3.14 Overview: A protein’s specific shape determines its function • A protein, such as lysozyme, consists of polypeptide chains folded into a unique shape • The shape determines the protein’s function • A protein loses its specific function when its polypeptides unravel. Milk curdles and egg white solidifies when their proteins are unraveled. Mad Cow Disease is caused by a malformed protein. Figure 3.14A Figure 3.14B

13. 3.15 A protein’s primary structure is its amino acid sequence 3.16 Secondary structure is polypeptide coiling or folding produced by hydrogen bonding Primarystructure Amino acid Secondarystructure Hydrogen bond Pleated sheet Alpha helix Figure 3.15, 16

14. 3.17 Tertiary structure is the overall shape of a polypeptide and due to R group interactions 3.18 Quaternary structure is the relationship among multiple polypeptides of a protein Tertiarystructure Polypeptide(single subunitof transthyretin) Quaternarystructure Transthyretin, with fouridentical polypeptide subunits. Transthyretin carries thyroid hormone through the blood. Figure 3.17, 18

15. 3.19 Talking About Science: Linus Pauling contributed to our understanding of the chemistry of life • Pauling made important contributions to our understanding of protein structure and function. He is often considered one of the founders of molecular biology. Figure 3.19

16. NUCLEIC ACIDS 3.20 Nucleic acids are information-rich polymers of nucleotides • Nucleic acids such and DNA and RNA serve as the blueprints for proteins • They ultimately control the life of a cell

17. Each nucleotide is composed of a sugar, phosphate, and nitrogenous base • The monomers of nucleic acids are nucleotides Nitrogenousbase (A) Phosphategroup Sugar Figure 3.20A

18. DNA has four kinds of bases, A, T, C, and G Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines Purines Figure 10.2B

19. Note the designation of the Carbons as 1-5.

20. DNA and RNA are polymers of nucleotides • DNA is a nucleic acid, made of long chains of nucleotides Phosphate group Nitrogenous base Nitrogenous base(A, G, C, or T) Sugar Phosphategroup Nucleotide Thymine (T) Sugar(deoxyribose) DNA nucleotide Figure 10.2A Polynucleotide Sugar-phosphate backbone

21. DNA consists of two polynucleotides twisted around each other in a double helix. The sugar is deoxyribose. The bases are adenine, thymine, guanine, and cytosine. • The sequence of the four kinds of nitrogenous bases in DNA carries genetic information Basepair Nitrogenousbase (A) Figure 3.20C

22. DNA is Antiparallel

23. RNA is single stranded and the sugar is ribose. The bases are adenine , uracil, guanine and cytosine. DNA RNA

24. The Bases of RNA

26. In most organisms, stretches of a DNA molecule, called genes, program the amino acid sequences of proteins. Retroviruses use RNA as their genetic material. The Dogma is not always correct. • The Central Dogma. Dogma (the plural is either dogmata or dogmas, Greekδόγμα, plural δόγματα) is the established belief or doctrine held by a religion, ideology or any kind of organization, thought to be authoritative and not to be disputed or doubted. Wiki • DNA information is transcribed into RNA, a single-stranded nucleic acid • RNA is then translated into the primary structure of proteins