BIO202 Exam 1

• Weak bonds

  • Mostly occur in large molecules in the cell

  Why are they needed?

  – They allow very transient (temporary) association between molecules
• Properties of water:

  – Cohesive behavior

  – Ability to stabilize temperature

  – Expansion upon freezing

  – Solvent versatility
• Hydrogen bonds in water give it adhesive and cohesive properties
• Water has high specific heat. It requires more energy than many other substances to heat it up. This is because it is hard to break so many hydrogen bonds.
• The density of liquid water is greater than the density of solid water
• Polar bonds in water make it an active solvent, able to dissolve many substances
• Substances that increase the concentration of H+ are called acids

  Substances that increase the concentration of OH- are called bases
• Each pH unit is a 10x change in H+ concentration
• How do we keep pH constant? By using buffers
• Buffers release or absorb H+ ions when needed
• Most buffers are weak acids or bases
• Hydroxyls are polar
• carbonyls are polar
• carboxyl -COOH are negatively charged
• amino -NH2 is positively charged
• Sulfhydryl -SH is polar and participates in S-S bonds
• Phosphates -PO4 are negatively charged and bulky
• Glucose is a structural component of cells:

  -cellulose in cell walls

  -glycolipids and glycoproteins
• Polysaccharides are made from sugar monomers by removal of water
• Fatty acids are

  • sources of food
  • part of phospholipids
  • stored as fats (triglycerides)
• If the fatty acid chain has no double bonds (C=C) => saturated.

  If the fatty acid chain has double bonds (C=C) => unsaturated.
• Sterols

  • include cholesterol
  • function as components of the plasma membrane (contribute to membrane fluidity and rigidity due to their bulky structure)
  • precursors of steroid hormones
• Pyrimidines (6-membered ring)

  • Cytosine

  • Thymine

  • Uracil

  Purines (5-membered ring attached to 6-membered ring)

  • Adenine

  • Guanine
• In DNA, the sugar is DEOXYRIBOSE (lacks oxygen at position 2)

  In RNA, the sugar is RIBOSE (has oxygen at position 2)
• To form polymers (RNA, DNA), nucleosides are converted to nucleotides
• sugar backbone in dna is formed from phosphodiester bonds
• Nucleic acids are found in

  – Nucleus

  – Cytoplasm

  – Mitochondria

  • Chloroplasts –
  • Ribosomes
• Nucleic Acid Functions:

  – Storage of genetic information

  – Transfer of genetic information (mRNA)

  – Structural (rRNA)

  – Transport (tRNA)

  – Enzymatic activity

  – Regulation of gene expression
• 5’ end with free phosphate group

  3’ end with free hydroxyl group
• A-T has 2 bonds

  C-G has 3 bonds (more stable)
• Base pairing is used to:

  • Preserve information (during DNA replication)

  • Repair mistakes (during DNA replication)

  • Transfer information (transcription, translation)
• Types of RNA:– messenger RNA (mRNA)– transfer RNA (tRNA)– ribosomal RNA (rRNA)
• Transcription: mRNA transcribed from DNA template using RNA polymerase enzyme.
• Translation: tRNA brings amino acids to the ribosome where they are assembled into proteins according to the sequence on the mRNA molecule.
• Ribosomes• the organelle that reads the genetic code• It consists of almost 100 proteins and a special ribosomal RNA (rRNA)• It sets the reading frame, and moves along the length of mRNA, adding one amino acid at a time• Amino acids are added by an adaptor molecule called transfer RNA (tRNA)
• tRNA: shape of a clover. 3 loops
• Amino acids have a basic amino group and an acidic carboxyl group
• Proteins• They represent one half of the dry weight of the cell– Structure – Storage – Transport (hemoglobin in blood)– Hormones (insulin)– Receptors (hormonal receptors)– Contraction (actin, myosin in muscles)– Defense (antibodies)– Enzymes (catalyze chemical reactions)
• Primary structure• 20 amino acids can produce 20n combinations in a polypeptide of length n • Only the most stable and functional combinations survived in evolution• The specific sequence of amino acids in a protein constitutes its primary structure
• In the primary structure, the N-terminus corresponds to the 5`end. The C-terminus corresponds to the 3` end of the coding part of the gene