Biology 12: Unit 1 - Lessons 4-6

Functions of Lipids

Functions of Lipids

• Long-Term Energy Storage:

  • 9.1 calories/gram vs. 4.4 for carbohydrates & proteins  (energy production = different pathway than carbohydrate breakdown)

• Body Structure - Insulation, Padding:

  • helps human body retain heat, protects vital organs

• Cell Structure:

  • cell membranes = mostly phospholipids  - nervous tissue contains lipid

    Hormones:

    • steroid chemical messengers in blood  (testosterone, estrogen)

Fatty Acid

long chain of carbons with hydrogens attached, ending in carboxylic acid group (-COOH)

Saturated Fatty Acids:

• all single bonds between carbon atoms – no more hydrogen can be added 

*solid at room temp, harder to break down, in animals

• ex. butter and lard

Unsaturated Fatty Acids

• some double bonds between carbon atoms – more hydrogen can be added

*liquid at room temperature, healthier, found in plants

• ex. olive/vegetable oil

Trigylcerides (Neutral Fats)

• formed from dehydration synthesis of glycerol with 3 fatty acids (either saturated or unsaturated)

• broken down for energy, used for physical protection (adipose tissue under skin & surrounding organs)

• uncharged, non-polar, hydrophobic (water hating)

Phospholipids

• polar hydrophilic (water loving) head, nonpolar hydrophobic tail (2 fatty acids)

• responsible for cell protection,  lets molecules in/out of cell as part of cell membrane

• surrounds non-polar molecules 

  (tails insert into dirt - washes away)

steroids

• 4 carbon rings, molecules based on cholesterol

• hormones found in blood that act on specific tissues and act on DNA (control) 

• cholesterol = structural component of cell membrane,

• testosterone/estrogen = male/female sexual characteristics

• excess steroids broken down by liver

Protein Functions

• energy storage:

  • energy produced via alternative pathway than carbohydrate breakdown

• structural:

  • hair/nails (keratin)

  • connective tissue (ligaments, cartilage, tendons - collagen)

  • muscle fibres (actin, myosin)

• process facilitation:

  • hormones carry messages in blood (insulin)

  • antibodies recognize foreign substances,

  • enzymes (catalysts) speed up chemical reactions (pepsin)

• molecule transport: hemoglobin carries oxygen in blood,

  • channel proteins allow molecules through cell membrane

Protein Structure

Monomer: amino acids

made up of carboxyclic acid group, r group, and amine group

Difference between dipeptide, polypeptide and protein

Dipeptide: 2 amino acids, with peptide bond bringing the molecule together

Polypetide:short chain of amino acids (~ 2 - 20)

Protein: long chain of amino acids (~ > 75)

number of amino acids in humans & types

21 total- different atoms in R groups

• humans make 12 (non essential)

• 9 from food

Primary Structure (looks like a snake)

• 2D linear sequence of amino acids

• joined together via peptide bonds within polypeptide

• many different sequences = many different proteins

secondary structure

• 3D orientation in space of a polypeptide

• joined by hydrogen bonding between carboxylic acid and amino groups from different amino acids

• ex. alpha helix and beta pleated sheet

tertiary Structure

• 3D shape of polypeptide

• joined/differentiated by covalent, ionic, hydrogen bonds between R groups, resulting in the bending and twisting of the structure

quaternary structure

- arrangement of separate (2 or more)  polypeptide chains that contribute to shape, function

• ex. hemoglobin = 4 polypeptide chains interlocked in a specific way to carry 4 O₂  molecules in blood (attached to iron/heme group)

DNA functions

• makes up genes (sections of DNA that code for specific  proteins) which in turn make up chromosomes (folded up DNA)

• directs/controls cell activities such as cell division + protein synthesis

• undergoes mutations which are important to  process of evolution

RNA function

works with DNA to direct protein synthesis

Monomer of DNA & RNA

nucleotide

• Phosphate + 5 carbon sugar group (deoxyribose or ribose) + nitrogen containing base w/ either one ring (pyrimidine) vs.two rings (purine)

DNA structure (double helix)

• 2 antiparallel strands of nucleic acids in nucleus that wind around each other 

• each strand has a backbone of sugars + phosphates of joined nucleotides

• bases stick out, hydrogen bond with complementary bases of  other strand

• in chemical, it is missing an O compared to RNA

RNA structure

• single strand nucleic acid, formed from DNA template in nucleus

• migrates to cytoplasm during protein synthesis

• thymine is replaced by uracil

Pyrimidines

thymine & cytosine

Purines

adenine and guanine

complementary base pairing

attraction of a purine to a pyrimidine base

• achieved via hydrogen bonding

• 2 hydrogen bonds = adenine + thymine(uracil)

• 3 hydrogen bonds = cytosine + guanine

• within a DNA molecule %A = %T, %G = %C

ATP (adenosine triphosphate)

• single nucleotide (not in strand or double helix) that floats around blood as primary carrier of energy in cells

• adenine base + ribose sugar + 3 phosphates

• high bond strain within molecule (oxygen electronegativity)

• when phosphoanhydride bonds between phosphates  broken, energy released, producing: adenosine diphosphate (ADP) + phosphate (P)

• energy used by cell (ex. muscle contraction)