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Chemistry to Biology Cells, RNA, & DNA

Chemistry to Biology Cells, RNA, & DNA. ASTR 1420 Lecture 5 Sections 5.2 & 5.4. RNA based world. In the beginning of Earth life, the first life could not be based on DNA because DNA is too complicated to be created by mere “lucky” chemical reactions.

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Chemistry to Biology Cells, RNA, & DNA

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  1. Chemistry to BiologyCells, RNA, & DNA ASTR 1420 Lecture 5 Sections 5.2 & 5.4

  2. RNA based world • In the beginning of Earth life, the first life could not be based on DNA because DNA is too complicated to be created by mere “lucky” chemical reactions. • early life must have used a simpler molecule (e.g., RNA) • or, DNA was introduced externally?!?

  3. Organic Building Blocks Six essential chemical elements for Earth Life • Carbohydrates (= carbs) : providing energy to cells and make cellular structures  sugars, starches, cellulose, etc. • Lipids (aka fats) : store energy, make cell membranes • Proteins : versatile, essential molecules of cells • Nucleic acids : handling heritable information of cells – DNA and RNA

  4. Cells Typical Eukaryotic Cell • All living organisms are made of cells • Adult human body have 10-50 trillion cells!

  5. Monomer/Polymer • Glycogen: the carbohydrate that animals use to store energy is a polymer made of glucosemolecule contains 22 atoms Most life forms consist of small number of simple molecule types called monomers, which can join together in a repetitive sequence to become larger and more complex molecules called polymers. glucose

  6. Amino Acids • Most important monomer! • Basic building blocks of proteins,nucleotides, and sugars Carboxyl group Amino group • Different side chain (R) makes a different amino acid. • There are about 70 different amino acids in Nature

  7. Amino Acids : peptide bond to make a long chain • Basic building blocks of proteins,nucleotides, and sugars R

  8. Amino Acids : peptide bond to make a long chain • Typically, few hundred amino acids form a protein polymer. • Out of ~70 amino acids, only 20 are used in Earth life!! A strand of amino acids, part of a protein

  9. Chirality of Amino Acids • Chirality (handedness) For a given amino acid, there are two geometrical types: left-handed & right-handed • In non-biological environ: two types are equally found • In living organisms: only left-handed amino acids are found! Why? All Earth life forms were originated from a single ancestral life using only left-handed amino acids!?!

  10. DNA  Proteins • All Earth life have DNA, and DNA is the backbone of heredity. • Heredity  DNA replication • function of DNA (genes)  protein synthesis • What’s protein? • organic compound made of amino acids in a folded chain • essential part of organisms and participate in every process within cells • enzymes involved in matabolism • make cell stuctures • cell signaling, immune responses, etc.

  11. http://www.youtube.com/watch?v=qy8dk5iS1f0 DNA structure

  12. http://www.youtube.com/watch?v=hfZ8o9D1tus DNA replication

  13. http://www.youtube.com/watch?v=XO-2Z933AzM Protein synthesis

  14. Genes • Part of DNA strand representing any single function (e.g., instruction for one protein)

  15. Genetic code Codes for most amino acids really depend on just two letters  in the past, genetic codes were two letter based… • The set of rules for reading DNA. • Genetic “words” consist of three DNA bases in a row. For the purpose of protein building, each word represents either a particular amino acid or “start reading” or “stop reading”. • Genetic code is same for nearly ALL living organisms on Earth! common ancestor of all life on Earth!

  16. Mutation • Replicating the whole ~3 billion bases for human DNA takes only a few hours • About 1 replication error in billion chances • wrong base • deleted base • extra base • etc. • Most of these errors have no effect : Why? • about 95% of human DNA bases are “non-coding DNA” • Most significant change is from “deleted base”. • Due to this “error”, every individual living organism differ each other. • Mutation = molecular engine of evolution! • Any change in the base sequence of DNA Stumpy, a four-legged duckling at Warrawee Duck Farm, Copythorne, Hampshire, England (2007)

  17. Sickle-cell disease • Just one base change in one gene (Adenine  Thymine) • Most mutations are harmful, but occasional good mutations are being picked up by “natural selection”

  18. Another evidence of the common ancestor • Cells need Energy to function • The ATP molecule gives up energy when it splits into ADP and a phosphate group. • ATP/ADP are like battery • ATP : fully charged • ADP : fully discharged Adenosine diphosphate

  19. Another evidence of the common ancestor • Cells recyle ATP. • There are many other possibilities of different molecular pairs (i.e., different batteries), but all Earth life use ADP/ATP as the energy reservoir.  common ancestor of all Earth life!

  20. In summary… Important Concepts Important Terms amino acids / proteins chirality genes, genetic code mutation • Common ancestor of all Earth Life (chirality of amino acid, common genetic code, and use of ATP among all living organisms on Earth) • Some non-DNA based life forms in the beginning? • DNA replication • Chapter/sections covered in this lecture : 5.2& 5.4

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