BABS1201 - Notes Cell Structure • Most abundant elements in universe are carbon, hydrogen, helium and oxygen

• Major elements of life are C, H, O, N, P, S

• These are in uniform amounts relative across organisms

• Life is diverse

• 1.8 million species identified

• 10 million species estimated (on Earth)

• 4 Characteristics of life: reproduce, grow & develop, respond to environment, metabolise to use and generate energy

• Cell: the smallest unit of organisation that can perform all the activities essential for life (simplest group of matter that is considered a living entity)

Classification

• Scientists classified life into species and broader classifications

• Initially done by examining structures, functions and other obvious features

• Currently, nucleic acid comparisons are used eg. 16s rRNA gene for bacteria

• Each species has a two-part name (Genus species)

• RNA is used to classify the 3 domains

• Prokaryotes: Bacteria (d), Archaea (d)

• Eukaryotes (d): Animal (k), Plant (k), Fungi (k), Protists (k)

Prokaryotes vs. Eukaryotes

Prokaryote Eukarote

DifferencesSize of bacteria is 1-5 µm Size of eukaryotic cells is 10-100 µm

No membrane-bound organelles Membrane-bound organelles, including a nucleus

Similarity

Plasma membrane is a selectively permeable barrier that surrounds the jelly-like cytosol inside the cell

Ribosomes are the protein factories of the cell. They are macromolecules made of ribosomal RNA and protein (therefore not considered organelles)

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Explaining Origin of Eukaryotes - Endosymbiotic theory

• Ancestors of eukaryotes engulfed O2 with non-photosynthetic prokaryotic cells

• This process is called endocytosis (uptake by invagination of membrane)

• Symbiosis occurred (mutual benefit) → merged into a single organism over long period of time

✦ Evidence suggests chloroplasts developed from endocytosis of cyanobacteria (photosynthetic bacteria)

✦ Also, other evidence include the double membrane of the organelles as well as the similarity of the 16s rRNA to the one found in bacteria

Macromolecules

• Theses are large chain-like molecules called polymers (made of similar/identical monomers linked by covalent bonds)

• Synthesis and Breakdown are both catalysed by enzymes:

• Synthesis: dehydration to form new covalent bond

• Breakdown: hydrolysis to split a covalent bond

• E.g. digestion

Carbohydrates

• Monosaccharides

• There is diversity in:

• Location of carbonyl group which determines whether the sugar is aldose (eg. Glucose) or ketose (eg. Fructose)

• Spatial arrangements around the asymmetric carbons (eg. Glucose vs. galactose)

Macromolecule Monomer

Carbohydrate Monosaccharide

Lipid Fatty acid

Protein Amino acid

Nucleic acid Nucleotide

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• Disaccharides are two monosaccharides joined by a glycosidic bond eg. maltose

• Polysaccharides are 100s to 1000s of monos joined by glycosidic bonds eg. starch

Lipids

• Lipids are hydrophobic (non-polar) macromolecules

Storage Structural

STARCH (polymer of glucose):• Stored by plants as granules within various

cellular structures.• This stored energy can be later accessed

by hydrolysis

CELLULOSE (polymer of glucose):• Major component of plant cell walls

GLYCOGEN (highly branched polymer of glucose):• Stored by animals mainly in liver and muscle

cells. • Hydrolysis of glycogen releases glucose when

the demand for energy increases (but it cannot sustain an animal for a long time)

CHITIN (polymer of glucose with N groups):• Found in exoskeletons of arthropods (insects,

spiders, crustaceans etc.)

Form Function

Energy Transport and Storage Fats (Triacylglycerol or TAG)

Structure Phospholipid, sterols

Chemical Messengers Steroids (eg. cholesterol), glycolipids

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