Download Unit 3 Biology - moleculesoflife2

Unit 3 Biology
Study 1
Molecules of life
Text: Heinemann 2. 4th Edition
Cells – The basic unit of life. Atoms are the basic building block of matter and they
create cells. Cells are the result of chemical compounds being formed for a purpose.
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The cell theory states:
All organisms are composed of cells and their products,
All cells come from pre-existing cells,
The cell is the smallest living organisational unit.
All cells perform similar processes and some have specialised functions.
Cell activities are carefully regulated and are catalysed by enzymes.
Cell structure
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There is no such thing as a typical cell but all cells share some features.
The cytoplasm is enclosed within an outer plasma membrane that separates it
from its environment and contains the genetic material.
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Two main types of cells: Prokaryotes and Eukaryotes.
Prokaryotes
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These include bacteria and cyanobacteria
These are small and lack membrane organelles.
Have a single circular DNA chromosome.
The plasma membrane is surrounded by an outer cell wall of protein and complex
carbohydrate.
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The cell wall in plants is composed of cellulose and in fungi; the cell walls are
composed of chitin.
Eukaryotes
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These have an internal membrane system that forms a nuclear membrane and
membrane around other organelles.
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Eukaryotes develop into multicellular organisms and are often referred to as
“higher organisms”
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Prokaryotes are sad to have been the precursor to eukaryotes according to the
evolutionist theory.
Cellular chemistry
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There are 92 naturally occurring elements.
C, H, O, and N make up 99% of an organisms weight.
Atoms are the basic unit of all matter.
Substances consisting of only one kind of atom are called elements.
Molecules are two or more of the same (or different kind) of atoms held together
by chemical bonds.
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A compound is a molecule containing more than one type of atom.
Chemistry of cells
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These have an outer membrane known as a plasma membrane.
DNA is located in a nucleus contained with a nuclear membrane.
DNA is formed into thread like structures known as chromosomes.
Organelles are encased in a membrane.
Organelles are subcellular structures that carry out a specific function.
Note: Plant cells and prokaryotes have a cell wall. Animal cells do not.
Water
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Most organisms have 70 – 90% water in their makeup.
Cellular activities occur in a watery environment.
The water in organisms needs to have the correct pH, ion concentration,
temperature, salinity and degree of cohesiveness.
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Oxygen is not very soluble in water. That is why fish require gills.
Carbon is the key atom in organic molecules. Plants take this from the air during
photosynthesis
Nitrogen
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Nitrogen is required in large amounts by all organisms to make protein.
Atmospheric nitrogen (78% is found in the air) is taken in by bacteria during
“nitrogen fixation” and is then directly taken up by plants through their roots.
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Symbiotic bacteria located on the roots of plants are vital in this process.
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Other useful minerals include phosphorous, potassium, mg, Na, S, and I.
Humans require at least 20 different mineral types.
Carbohydrates
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There are 4 main types of organic molecules. These are carbohydrates, lipids,
proteins and nucleic acids.
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Carbohydrates – Stored as starch for energy in plants, structural cellulose in plants
and glycogen in animals.
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Carbohydrates are made from C, H, and O.
Monosaccharides are single sugars such as glucose.
Disaccharides = two sugars
Polysaccharides = many sugars.
Lipids
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Lipids are fatty substances and include fats and oils. They are energy rich (37kj
per gram).
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Made from C, H and O. Similar to Carbohydrates but in different proportions and
can have other elements such as N and P added.
Proteins
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Proteins are the most complex of the organic compounds.
Proteins are made from C, H, O and N.
They are made from sub units known as amino acids. There are 20 different types
of amino acids.
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In medicine, 99% of all drugs are proteins.
Examples of proteins include hormones, enzymes and blood hemoglobin.
They are used to build cell structure.
Nucleic acids
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Nucleic acids are the genetic material of all organisms.
Two types include DNA (deoxyribonucleic acid) and RNA. (Ribonucleic acid)
Both are created from long chains of units known as nucleotides.
DNA carries genetic instructions required to assemble the proteins.
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RNA plays a major role in the building of proteins on organelles known as
ribosome's found in cells.
Protein structure.
Proteins are amino acid chains that fold into unique 3 dimensional structures.
The shape into which a protein naturally folds is known as its native state,
which is determined by its sequence of amino acids. Thus proteins are known
as polymers, with amino acids being the monomers. Biochemists refer to four
distinct aspects of protein structure.
Primary structure. – The amino acid sequence.
Secondary structure – highly patterned sub-structures. (Alpha helix, beta
sheet, or segments of chain that assume no stable shape)
Tertiary structure – the overall shape or structure that results from the union of
more than one protein molecule,
Quaternary structure – the shape or structure that results from the union of
more than one protein molecule, usually called subunit proteins.