BIOLOGY Chapter 3-lecture 6 Dr. C. Doumen. Lipids

Transcription

1 BIOLOGY 1408 hapter 3-lecture 6 Dr.. Doumen Lipids v Lipids are diverse compounds that are grouped together because they do not mix well with water. hey are thus hydrophobic. Why? v ll lipids consist mainly of carbon and hydrogen atoms with just a few functional groups ave large hydro-carbon chains Linked by nonpolar covalent bonds ydrophobic (water-fearing) v Lipids don t form huge macromolecules or polymers like sugars, proteins and nucleic acids do. 1

2 Lipids v Lipids are classified according to their organization. he major classes are : v Fats ( also called neutral lipids, triglycerides) v Phospholipids v holesterol based lipids Fats v he fats are also called the tri-glycerides v fat is a combination between 3 fatty acids and a molecule of glycerol. v fatty acid is a long hydro-carbon chain ending with a carboxyl group. In a simple way, we can write a generic fatty acid as follows: 3 - ( 2 ) n - OO hydrocarbon tail carboxyl group 2

3 Example of a fatty cid Saturated vs Unsaturated Fatty cids v Some fatty acid will have the maximum number of hydrogens on their carbons ( thus no double bonds between carbon atoms) v hose are called the saturated fatty acids v If a double bond is present, it is is called an unsaturated fatty acid (mono-unsaturated contain 1 double bond per fatty acid; poly-unsaturated contain 2 or more). 3

4 Examples riglycerides v ri-glycerides are a linkage of 3 fatty acids to a glycerol molecule Fatty acid where R represents the rest of the fatty acid chain Glycerol In a dehydration synthesis reaction, water (the O) will be removed to form a covalent bond between each fatty acid and the glycerol molecule 4

5 riglycerides Dehydration synthesis linking one fatty acid to glycerol Do this 3 times and we have a tri-glyceride 5

6 Fats and Fatty cids v So why is this fat hydro-phobic? v Once the fatty acid hook up with glycerol, no functional groups are left; they are all involved in a bond v It is mostly hydro-carbons with a few buried oxygens. Fats and fatty acids v riglycerides are fats from the food we eat that are carried in the blood. Most of the fats we eat, including butter, margarines and oils, are in triglyceride form. v Excess calories, alcohol or sugar in the body turn into triglycerides and are stored in fat cells throughout the body. v his is your long term energy reservoir molecule. When you are low on carbohydrates, your body will start using these fats. 6

7 Fats and Nutrition v v v Fats with saturated fatty acids tend to pack closer to each other and form aggregates easier nimal fats are mostly made from saturated fats and thus are in general solid at room temperature Plant Oils contain mostly unsaturated fats (liquid at room temp.) Fats and Nutrition v v v he general consensus is to reduce food with larger amounts of animal fat (saturated fats). he body can synthesize most of the fats it needs from the diet. owever, two essential fatty acids, linolenic and linoleic acid, cannot be synthesized in the body and must be obtained from food. hese basic fats, found in seafood, plant, nuts, are used to build other specialized fats called omega-3 and omega-6 fatty acids. 7

8 Fats and Nutrition v v v Omega-3 and omega-6 fatty acids are important in the normal functioning of all tissues of the body and seem to be essential to fight inflammation. typical merican diet has way too much Omega 6 compared to Omega 3 his imbalance seems to be at the basis of modern western diseases. Fats and Nutrition 8

9 PhosphoLipids v phospho-lipid is a special case of a tri-glycerides Polar head region v One of the fatty acids has been replaced with a functional charged phosphate group. v he molecule becomes hydrophillic at one end (the polar head) and remains hydrophobic at the other end due to the two fatty acid tails. v Phospholipids are essential in creating cellular membranes. Steroids ll steroids are made from the basic cholesterol molecule v cholesterol is a main component in cell membranes v cholesterol, is also important since it is the basic structure for making a variety of hormones. 9

10 v nabolic steroids are synthetic variants of the male sex hormone testosterone Steroids v hey thus will mimic the real hormone ; sometimes with good, often with bad side effects (mood swings, infertility, cancers, inappropriate muscle mass, skin rashes, baldness, ) Proteins v Proteins are essential to the structures and activities of life v Proteins are the most variable of macromolecules and thus perform an enormous variety of functions. v Proteins are involved in all aspects of cellular activity v hey can be functional such as enzymes, antibodies, hormones or structural such as collagen, nails, hairs. 10

11 Proteins v he basic building block (the monomer) of all proteins are amino acids. protein is thus a polymer of amino acids typical amino acid has O central carbon carboxyl group on one end n amino group on the other end variable group (R) mino group N R O arboxyl (acid) group Proteins v here are 20 different amino acids, their differences due to a change in the R group. v Each amino acid will thus have different characteristics O O O N N N 2 O 2 O 2 O 3 3 Leucine (Leu) ydrophobic O Serine (Ser) ydrophilic O O spartic acid (sp) 11

12 Proteins v ells link amino acids together by dehydration synthesis v he bonds between two amino acid monomer is called a peptide bond and forms a di-peptide arboxyl group mino group Peptide bond N R O O + N R O O Dehydration reaction 2 O O N N R R O O mino acid mino acid Dipeptide Figure 3.12 Proteins v Many amino acids together form a polypeptide. v Polypeptides can be several to thousands of amino acids long. v he different ways the amino acids are strung together determine the kind of polypeptide it becomes v he code for that arrangement is located in the genes in the DN v functional protein can be one polypeptide or a combination of several polypeptides. 12

13 Protein Structure v Proteins become functional when they fold the proper way into a 3 dimensional structure v hat proper folding is determined by the linear sequence of amino acids and how they eventually will interact with each other v Primary structure of a protein = he linear sequence of in a protein v ertiary structure = the 3-dimensional folding of the protein v Quarternary structure = when different polypeptides interact to form one (1) functional protein Protein Structure he primary sequence tells us exactly in what position an amino acid is located. hanging the location of 1 amino acid may result in a non-functional protein (protein may not fold right) 13

14 Protein Structure orrect folding creates the unique shape that determines the protein s function Protein Structure he correct folding of a polypeptide creates regions and grooves that enable the protein to execute its function Groove Groove 14

15 Protein Structure he nicotinic Na-channel is an example a quaternary level protein made out of 5 polypeptides (subunits), forming a channel barrel system. Protein Structures emoglobin is another example a quaternary level protein made out of 2x2 polypeptides (2 alpha and 2 beta subunits), forming an O 2 carrying protein. here are about 280 million emoglobin molecules in each red blood cell. 15

16 Protein Structure Denaturation : when the 3-dimensional structure falls apart due to changes in temperature or p. his will result in loss of function. Protein Structure We boil things to denature proteins and thus reorganize the structures for better taste or to kill the function of proteins that could possibly harm us. Exposing proteins to extreme acids or bases also denatures them ( what happens when you add lemon juice to milk? ) 16

17 Nucleic cids v he nucleic acids form the last group of macromolecules of living cells v here are two main types of nucleic acids v DN = deoxy ribose nucleic acid v RN = ribose nucleic acid Nucleic cids v ll information to make all structures of an organism is located in the chromosomes, which are bundles of macromolecules, mostly made out of DN v he linear sequence of a protein of an organism for example, is coded within a gene, which is a specific sequence within the DN of that organisms chromosomes. 17

18 Nucleic cids human karyotype : a display of all the chromosomes of an individual. Nucleic cids v he chromosomal DN contains thousands of genes and each gene codes for a protein. v he genes however do not make the proteins directly v Information is first passed on to another molecule called RN 18

19 Nucleic cids v he flow of information is thus from DN to RN first: this is called transcription v protein is then manufactured off this RN information : this is called the translation process. Nucleic cids v Nucleic acids such as DN and RN serve as the blueprints for proteins and thus control the life of a cell v he monomers (building blocks) of nucleic acids are nucleotides. v hey are composed of v a 5 carbon sugar, v a phosphate group v a nitrogenous base O O P O O - Phosphate group 2 O N N N N N Nitrogenous base () O Sugar 19

20 v Nucleic cids are formed by stringing Nucleotide monomers together using the sugars and phosphates as the backbone v he nitrogenous bases will stick out like the steps of a ladder. Nucleic cids Nucleic cids: DN Nucleotide here are 4 such bases in DN : adenine (), thymine (), cytosine ( ), and guanine (G) G v DN never appears as a single strand v It will always be coupled in a helical fashion with another complementary DN strand. Sugar-phosphate backbone 20

21 Nucleic cids: DN G G v here is only one complementary strand of DN that can pair up with an existing DN strand Base pair G G v his is due that a nucleotide with an base can only form hydrogen bonds with a nucleotide on the other strand that has a base. v nd G always pairs up with v he result is a double helix of DN held together only by hydrogen bonds. Nucleic cids: DN G G v Because of this base pair ruling, the two strands are called complementary (mirror images almost) Base pair G v If you know the sequence on one strand, one can predict the sequence of bases on the other strand G v -G- on one strand must read as -GG- on the other strand. 21

22 Nucleic cids: RN v While DN is a double stranded helix (double helix), RN is usually single stranded v RN also has a different sugar compared to DN : DN has a deoxy-ribose sugar, RN has a ribose sugar ( they differ only the the absence/presence of one oxygen atom). v nother difference is that hymine () is not present in RN : it becomes replaced with a different base called Uracil (U). Nucleic cids: RN While DN is a double stranded helix ( double helix), RN is single stranded 22

23 Nucleic cids: RN While DN has deoxyribose as the sugar in nucleotides, RN has ribose as the sugar while the thymine base becomes replaced with Uracil. DN pplication : Forensics Electrophoretic analysis of DN yields a unique pattern called a DN fingerprint. 23

24 DN Forensics v Depending on the technique used, a person s DN shows up just like a Barcode v In this case, only a few markers identified individuals, but enough markers were present to identify the suspect. DN umor 24