Biology: Characteristics of Life & Cell Structure

• Test 1 will be the 2nd tutorial of Week 8.
• The test is a closed book Moodle exam.
• The test format includes 30 multiple choice questions.
• 45 minutes are allowed to finish the test.
• The test is worth 20% of the final course mark.
• Attendance in the tutorial class is compulsory to sit in the mentioned exam.
• Absence results in a zero mark.
• Lecture content from weeks 1-6 is covered including photosynthesis.
• Lab 1 Introduction to lab safety including PPE and correct waste disposal is covered.
• Lab 2 Cell structure including differences between prokaryotic and eukaryotic cells, microscope parts and function, and scale calculation is covered.
• Tutorials on cell structure, scientific literature, cell membranes, macromolecules, scales, cellular respiration, and photosynthesis are covered.

Characteristics of Life

• All living things reproduce, grow, develop, respond to their environment, and metabolize to use and generate energy.
• A cell's organization performs life's essential activities.

Unicellular vs Multicellular

• Organisms can be either unicellular (composed of one cell) or multicellular (composed of more than one cell).
• Most life on earth is unicellular.
• Multicellular organisms have cells organized into tissues, then organs, then organ systems.
• Bacteria, archaeans and protists are examples of unicellular organisms.
• Animals, fungi, plants and some algae are examples of multicellular organisms.

Domains of Life

• Life is classified into three domains at the highest level: Bacteria, Archaea, and Eukarya.

Water and Life

• Water is necessary for life because nearly all biological molecules assume their shapes and functions based on its physical and chemical properties.
• Most biochemical reactions occur in water.
• Reactions involving water allow many processes to support life.
• Living organisms are located where there is water.

Properties of Water

• Cohesion and adhesion affect the properties of water.
• Water displays tension.
• Water is an excellent solvent.
• Ice is less dense than liquid water.
• Water can be ionized, which can act as either an acid or base in reactions.
• Water is composed of two hydrogen atoms and one oxygen atom covalently bonded.
• Oxygen is more electronegative than hydrogen, resulting in a polar molecule and unequal sharing of electrons.

Elements of Life

• The major elements of life are carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur (CHONPS).
• CHONPS are present in uniform relative amounts across organisms.
• DNA includes carbon, hydrogen, oxygen, nitrogen, and phosphorus.

Cells

• A cell is the smallest unit of organisation that can perform all activities essential for life.
• The two cell types are prokaryotic and eukaryotic; bacteria and archaea are prokaryotic domains, and eukarya is a eukaryotic domain.
• Cytosol is jelly-like aqueous fluid filling a cell's cytoplasm, containing salts, minerals and organic compounds.
• All cells have a selective barrier that controls the intracellular environment.
• DNA, replication, and protein production are the same in all cells.
• Protein synthesis occurs on ribosomes in all cells.
• Nearly every cell function requires proteins, the protein makeup is at least 20 amino acids, where DNA is transcribed to RNA.
• Prokaryotic cells have a nucleoid, plasmid, ribosomes, plasma membrane, cell wall, capsule, and flagellum.
• Eukaryotic animal cells have an endoplasmic reticulum (ER), a nuclear envelope, a nucleolus, chromatin, a plasma membrane, and ribosomes.
• Eukaryotic plant cells have a central vacuole, chloroplasts, in addition to other organelles.
• Mitochondria and chloroplasts evolved in eukaryotic cells through endosymbiosis.
• Further evidence for endosymbiosis includes similarities in size between prokaryotic organisms, mitochondria, and chloroplasts (1-10µm).
• Structures also all have their own DNA, ribosomes and divide through binary fission.

Endomembrane system – Nucleus and RER

• Nucleolus function - site of ribosomal RNA transcription (manufactures ribosomes).
• Chromatin function - DNA wrapped around proteins called histones so DNA can fit within the cell.
• Mitochondrion - energy production.
• Rough ER synthesizes proteins and lipids.
• Golgi - modifies, sorts and stores proteins.
• Cell membrane - protection, transport, selectivity permeable, and maintains cell integrity.
• Nucleoid contains genetic instructions for cell development and function.
• Cytosol/cytoplasm - liquid component of cytoplasm surrounding the organelles where cell processes occur.
• Cell wall - structural integrity and shape of cells.
• Cell membrane - permeability barrier, energy conservation and protein anchor.

Mitochondrion

• Outer membrane
• Inner membrane
• Matrix containing soluble enzymes catalyzing oxidation of pyruvate and small organic molecules, and as the site of the TCA cycle.
• Inner membrane contains complexes of the electron transport chain and the ATP synthase complex.

Macromolecules

• Macromolecules for life include carbohydrates, lipids, proteins and nucleic acids.

Carbohydrates

• Storage carbohydrates in plants and animals include starch.
• Structural carbohydrates include cellulose in plants and chitin in some animals.

Lipids

• Three fatty acid molecules each join with glycerol by an ester bond creating a fat called triacylglycerol (TAG) or triglyceride.
• Essential to cells because they make up cell membranes.
• Consists of a hydrophilic (polar) head group and two hydrophobic tails.
• Structure is similar to triacylglycerol (TAG) except that phosphate and a polar group are the replacement for one of the fatty acids.
• Three fatty acid molecules each join with glycerol by an ester bond creating a fat called triacylglycerol (TAG) or triglyceride.

Proteins

• Polymers of amino acid monomers are called polypeptides.
• A protein consists of one or more polypeptides, each folded into a specific three-dimensional structure.
• Twenty different amino acids are used by cells to build their thousands of proteins.
• Amino acids have a common structure with a central carbon, an amino group in ionic form, a carboxyl group in ionic form, a hydrogen atom, and a variable R-group side chain.
• Protein provide functions of enzymatic activity, defenses, provide storage, assist with transport substances and hormone coordination in addition to producing receptors, contractile movement and support structure.

Cell Membrane

• The membrane of a cell as described as "fluid" since the lipids and proteins that move, make up its hydrophobic integral components.
• The cell membrane is described as "mosaic" since it’s made up of made up many different parts/kinds of macromolecules such as proteins, glycoproteins, glycolipids, and in some cases cholesterol and phospholipids.
• Small hydrophobic molecules such as oxygen can diffuse easily through the cell membrane.

Transport

• Active transport moves molecules against the concentration gradient.

Aerobic Cellular Respiration

• Aerobic cellular respiration consists of glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation.
• During oxidative phosphorylation, chemical energy is derived from an electron transport chain and chemiosmosis.
• During the electron transport chain and the pumping of protons, an H+ gradient is created across the membrane.
• Oxidation of NADH occurs at step one within the electron transport chain.
• ATP is produced with chemiosmosis and using ATP synthase.
• Energetic electrons, taken from glucose, are stripped of energy to actively transport H+ into the intermembrane space.
• ATP synthase in the inner mitochondrial membrane makes ATP using the electrochemical gradient to allow the movement of H+.
• Light reactions in photosynthesis contribute to the H+ gradient, which increases concentration in the thylakoid space.
• Photosynthesis starts by splitting water and pumping hydrogen ions (H+) into the thylakoid space.
• ATP synthase is powered via diffusion from thylakoid space back into the stroma, storing chemical energy in NADPH and ATP which then shuttles energy to the Calvin cycle.