Understanding Lipids and Fatty Acids

Lipids

• Lipids are insoluble in water, yet soluble in nonpolar solvents like ether, chloroform, and acetone
• Lipids comprise carbon, hydrogen, and oxygen
• Fats are solid at room temperature, whilst oils are liquid
• Lipids are polymers of fatty acids and glycerol molecules

Fatty Acids

• Fatty acids have a general formula of CH3(CH2)nCOOH
• Contain the acidic or carboxyl group -COOH
• Two primary types of fatty acids exist, depending on the presence or absence of double bonds, these are saturated and unsaturated fatty acids

Unsaturated Fatty Acids

• Unsaturated fatty acids contain one or more double bonds in their structure
• Double bonds reduce the melting point, making the lipids or fatty acids melt more readily
• Most oils are unsaturated
• Fatty acids or lipids with more than one double bond are polyunsaturated
• Fatty acids or lipids with only have one double bond are monounsaturated
• Plant lipids are often unsaturated and exist as oils, for example, olive and sunflower oil

Saturated Fatty Acids

• Saturated fatty acids lack double bonds in their carbon-carbon chain
• All saturated fatty acids are solid at room temperature
• Animal lipids are frequently saturated and present as animal fat
• Fats can be stored in the body under the dermis of the skin and around the kidney

Phospholipids

• Phospholipids are a subset of lipids
• They possess one water-soluble end
• One of the three fatty acid molecules is replaced by a phosphate group
• The phosphate group is hydrophilic, water-loving, and makes up the head of the molecule
• The tail of a phospholipid molecule is hydrophobic or water-hating

Lipid Functions

• Fatty acids function as stored energy
• Lipids are structural components in cell membranes, such as phospholipids
• Lipids are precursors for synthesizing Vitamin D and bile
• They are precursors to adrenal cortex hormones, such as cortisol and aldosterone
• Lipids are precursors to sex hormones like progesterone, estrogen and testosterone
• Lipids act as poor conductors of heat to provide insulation
• Lipids serve as protective coatings for skin, fur, feathers, fruit and plant leaves, for example, wax
• The shiny appearance of fruits and plant leaves is due to waxes
• Waxes act as a water barrier for animals, birds and insects

Proteins

• Proteins are biological molecules primarily made up of carbon, hydrogen, oxygen, and nitrogen
• Proteins sometimes also include phosphorus and sulfur
• Proteins have the general formula RCH(NH2)COOH
• 'R' represents a group that varies in structure and composition, known as a side chain
• Proteins are biological molecules formed of amino acid monomers
• Proteins can be structural, regulatory, contractile, or protective
• Proteins function in transportation, storage, and in membranes
• Protein structure and function varies greatly
• Proteins comprise more than 50% of the dry mass of most cells
• Protein-rich foods include meat, cheese, milk, fish, beans, and vegetables

Amino Acids

• Amino acids possess a central carbon atom bonded to an amine group (-NH2), a carboxylic acid group (-COOH), and a hydrogen atom
• The only difference between amino acids is the fourth group of atoms or 'R' group bonded to the central carbon

Examples of Amino Acids

• Alanine
• Valine
• Lysine
• Aspartic acid

Peptide Bonds

• Peptide bonds are formed through the loss of a hydroxyl (-OH) group from the carboxylic acid group of one amino acid
• Also the loss of a hydrogen atom from the amine group of another amino acid joins the amino acids
• This process leaves a carbon atom of the first amino acid free to bond with the nitrogen atom of the second
• The oxygen and two hydrogen atoms that are removed combine to form a water molecule

Polypeptides

• Ribosomes are the place where amino acids are joined together to form polypeptides in living cells
• The reaction forming polypeptides is controlled by enzymes
• Polypeptides are broken down into amino acids through the breaking of peptide bonds
• Breaking down polypeptides in this way is a hydrolysis reaction

Globular Proteins

• Globular proteins are ball-shaped whose molecules curl up in that shape
• Examples of globular proteins are myoglobin, haemoglobin, and antibodies
• Globular proteins exclude water molecules from the center of their folded structures
• play a role in metabolic reactions

Fibrous Proteins

• Fibrous proteins do not coil into a ball. Instead, they form long strands
• They are typically insoluble in water and serve structural purposes
• Keratin forms hair, nails, and the outer layers of skin
• Collagen builds skin, tendons, cartilage, bones, teeth, and blood vessel walls

Protein Functions

• Proteins can be structural, can act as Enzymes, or Hormones
• Protein enzymes include DNA polymerase, lysozyme, nitrogenase and lipase
• Hormones include growth hormone (GH) and follicle-stimulating hormone (FSH)
• Proteins can act as respiratory pigments, such as, haemoglobin and myoglobin
• Proteins can transport, for example, channel proteins and carrier proteins
• Motor proteins enable muscle contraction and relaxation, such as, actin, myosin, kinesin and dynein
• Some function as storage, such as, ferritin, ovalbumin, and casein
• Toxins are also molecules made of proteins, such as, diphtheria toxin, Pseudomonas exotoxin, and ribosome-inactivating proteins

Nucleic Acids

• Nucleic acids are macro chemical molecules, comprised of phosphoric acid, sugars, and organic bases
• Nucleic acids are principal information-carrying molecules in cells
• Direct protein synthesis and determine the inherited features of every living thing

DNA and RNA

• DNA stands for deoxyribonucleic acid
• RNA stands for ribonucleic acid
• Nucleotides are the smaller molecules that form DNA and RNA
• DNA and RNA are polynucleotides, being formed of a chain of nucleotide mers
• Genes are stretches of DNA that code for RNA and amino acids, ultimately coding for proteins

Nucleotides

• Nucleotides are made up of a nitrogen-containing base, a pentose sugar, and a phosphate group.
• DNA contains the bases adenine, thymine, guanine, and cytosine
• RNA contains uracil in place of thymine

Pentose

• The pentose 5-carbon sugar can be either ribose, C5H10O5, as in RNA or deoxyribose, C5H10O4 in DNA
• The carbon atom in DNA has no oxygen atom

DNA and RNA Strands

• DNA consists of two interwoven strands of nucleotides creating a double helix
• RNA is smaller and single-stranded in comparison to DNA
• The three types of RNA are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA)

DNA Functions

• DNA stores information that is transferred to the next generation
• DNA is self replicating
• DNA specifies the biological development of all living organisms and viruses
• DNA carriers the genetic code or instructions for protein synthesis

RNA Functions

• RNA acts as genetic material in some viruses and possesses enzymatic activity in other organisms
• MessengerRNA (mRNA) moves the genetic code from DNA to ribosomes which are protein-synthesizing machinery
• TransferRNA (tRNA) aids protein synthesis, providing amino acids which are the building blocks of proteins
• RibosomalRNA (rRNA) forms a complex with proteins to make up the structure the ribosome

Cell Cycle

• A cell cycle is a sequence of events that occurs in a parent cell
• It consists of a sequence of events that distributes genetic material and forms daughter cells

Divisions of the Cell Cycle

• The 2 main divisions are interphase and cell division
• The phases within interphase are G1, S, and G2
• The first stage of interphase is G1 phase or first gap, a time when the cell is metabolically active
• S phase or Synthesis of DNA is the stage of DNA replication
• G2 Phase or second gap, is the stage where the cell replenishes energy stores and synthesizes proteins for chromosome manipulation and movement
• Cell organelles like the chromosomes are duplicated during the S and G2 stages
• Cell division includes nuclear division or Karyokinesis, Mitosis, M – stage, followed by cytoplasmic division (Cytokinesis)
• The cell division process always produces two identical daughter cells
• Cell division is internally controlled
• Uncontrolled cellular division yields cancer

The Cell Division Process

• Cell division is a basic process in all living things, where a parent cell divides into two daughter cells
• Two sub divisions are involved with cell division
• A. Nuclear division or Karyokinesis results in the separation and distribution of duplicated genetic materials or mother cells to daughter cell by mitosis or meiosis
• B. Cytokinesis involves the separation of the cytoplasmic components into the daughter cells

Mitosis

• A basic life process
• Mitosis is the division of somatic cells ie body cells
• During mitosis, a cell duplicates all of its contents, including chromosomes and organelles
• The duplicated chromosomes are then aligned, separated and moved into respective poles to form two new identical daughter cells

Mitosis Stages

• Prophase (the "first phase") involves the duplicated chromosome, composed of two sister chromatids
• Chromosomes shorten, thicken and become visible
• Also, centrosomes begin to move to opposite poles of the cell forming spindle fibers
• Metaphase has fully developed mitotic spindles, while the centrosomes are at opposite poles
• Chromosomes line up end-to-end along the center or metaphase plate of the cell
• Each sister chromatid is attached to a spindle fibre that come from opposite poles
• Anaphase is when the sister chromatids separate at the centromere
• The connection between the sister chromatids breaks down and the microtubules pull the chromosomes toward opposite poles
• Telophase involves a reversal of prophase
• What has disappeared during interphase will reappear during telophase
• The mitotic spindles are depolymerized
• The nuclear envelopes form around the chromosomes and nucleosomes appear within the nuclear area
• Cytokinesis is the division of the cell that is completed through physical separation of the cytoplasmic components
• Cytokinesis results in two genetically identical daughter cells
• In animal cells, cytokinesis enables the mother cell's cytoplasm to pinch or constrict in the middle
• Because a plant cell is surrounded by a cell wall, the cytoplasm cannot pinch off. Instead, there is a new wall laid down between the two the daughter cells

Meiosis

• Meiosis is a characteristic part of organisms that reproduce sexually
• Meiosis happens in reproductive organs specifically the ovaries for female animals, the testes of males, and the anther and ovules of flowering plants
• It involves two fissions of the nucleus providing four gametes, (sex cells)

Meiosis and Gametogenesis

• Meiosis is referred to as a reduction division, because the final daughter cells are haploid (n)
• During gametogenesis or gamete formation, human ovaries and testes reduce the 46 chromosomes in the initial mother cell to half. Thus 23 chromosomes by meiosis
• Sperm and egg join during fertilization to produce a zygote
• A zygote contains the normal number of 46 chromosomes or 23 pairs

Description of the different stages of Meiosis I and Meiosis II

• Prophase I sees each chromosome appear shortened and thickened so to form two chromatids Homologous chromosome pairs arise.
• Metaphase I sees chromosomes aligned on a spindle fibre along a metaphase plate
• Anaphase I means that the centromere joining sister chromatids do not separate, The 2 homologous pair of chromatids instead will move to opposite ends or "poles"
• Reduction to haploid (n) happens because it is homologous chromosomes that separates from the initial male and female parents during this phase
• Telophase I sees the nuclear membrane reforms and the cells begin to divide.
• In some cells, the cell continues to complete cytokinesis, whereas in other cells
• Chromosomes line up in the metaphase plate . Also sister chromatids or the remains of each chromosome come from the opposite poles.
• Some cells may experience a prolonged interphone to no duplication of DNA

Meiosis Part 2

• Prophase II involves that new spindles are formed and the chromosome, which is still made up of paired chromatids, will move toward the middle of the cell
• In Metaphase II, chromosomes line up in the metaphase plate, with the spindle attached to sister chromatids.
• Sister chromatids stem from each chromosomes coming from the opposite poles.
• Anaphase II is where the centromeres divide and sister chromatids separate. The now divided contents separate and pull to the opposite ends of each cell
• Telophase II is where a nuclear membrane reappears and a chromosome returns to the interphase state
• Ultimately, cytokinesis follows, where it yields four daughter cells. Each cell will possess or containhalf the chromosome number of those from the initial mother cell and the DNA is not yet duplicated

Dr. Melaku Worede

• Dr. Melaku Worede, is a geneticist and agronomist
• He is known for using science to benefit poor farmers and saving Africa's seeds from extinction
• Dr. Worede was awarded the "Right livelihood Award" in 1989 for preserving Ethiopia's genetic wealth
• He played the key role in establishing the genetic resource centre for Plants in Addis Ababa