The Leading Edge - VCE Biology

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mitochondrion. site of oerobic

respirotion

vesicles. cellulor

konsport

nucleus. DNA - genetic

inskuctionso RNA - proiein

synhesis

nucleolus

nucleor membrone. mony Pores. h,vo loyers

cytoplosmo cell conlents. cytosol - fluid

within the cell. onoerobic respirotion

endoplosmic reticulum. cqn be smoolh or rougho protein synthesis

plosmo membr<rneo phospholipid biloyero octive tronsport. diffusion. cell recognition

vqcuoleo provides turgidily

in plonts. involved in

woier regulotion

chloroplosto found only in

producers. ploce of

pholosynhesis

ribosomes. found only in

producersr protein

synthesis

cell woll. found only in

plonts ond fungi

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The Leading Edge - VCE Biology

The chemical nature of i cell. The cell theory states that all living things are made up of cells, that the cell is the

smallest living unit, and that new cells are made from pre-existing cells.. The structure of a cell depends on its specific function, but most cells have a few basic

things in common. All contain DNA within the cytoplasm, all of which is then enclosedby'a plasma membrane.

. There are two main cell types:r prokaryotic cells (bacteria and cyanobacteria) do not contain membrane-bound

. organelles. The DNA is a single chromosome in the shape of a ring

. eukaryotic cells have many different membrane-bound organelles within thecytoplasm, including a nucleus that contains several strand-like chromosomes.

Comparison of eukaryotic and prokaryotic cellsEukaryote Prokaryote

mitochondrion

endoplasmicreticulum

Four elements, carbon (C), hydrogen (H), oxygen (O) and nitrogen (N), make up 99% of allorganisms by weight. Atoms are the basic unit of all matter. Molecules are two or moreatoms held together by chemical bonds, and compounds are molecules containing more thanone atomic element.Organic compounds always contain carbon, and most also contain hydrogen. Moleculesthat do not contain carbon are inorganic compounds. Some very simple compoundscontaining carbon are also considered to be inorganic. lmportant inorganic molecules includewater, oxygen, carbon dioxide, nitrogen and minerals.Atoms within a molecule are bound together by strong forces called atomic bonds. Thedifferent properties of these bonds determine how the molecules move and interact withinthe cell.

lnorganic moleculesWater. Most living organisms are about 70-90% water.. Water is very cohesive (interconnected), has a high heat capacity (good at limiting heat

transfer) and is an excellent solvent for polar molecules.Oxygen and carbon dioxide. Oxygen is needed to release energy from food molecules (in respiration).. Carbon dioxide is the main source of carbon for organic compounds (by

photosynthesis).

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ribosome iell membrane

Write definitions for the following words:DNAcytoplasmplasma membrane

prokaryote

eukaryoteinorganic compoundorganic compound

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The Leading Edge - VCE Biology

Nitrogeno Nitrogen is 'fixed'from the atmosphere (by bacteria in the soil or plant roots) into

compounds that can be used by other organisms.Minerals. Small amounts of various minerals are used with organic molecules, e.g. enzymes.

Organic moleculesLarge organic molecules made up of chains of many smaller sub-units (monomers) arecalled biomacromolecules or polymers.

Carbo hydrates/polysacch arides. most abundant organic compounds in natureo major source of chemical energy. energy stores for plants and animals, e.g. starch and glycogen respectivelyo used in structural components of cellso part of DNA and RNA. combine with lipids and proteins to make membranes.Carbohydrates are made up of C, H and O. ln simple carbohydrates, the general formula isCn(H2O)r, e.g. glucos€ CoHrzOo.

The sub-units of carbohydrates are monosaccharides, 'single sugars' (e.9. glucose,galactose and fructose). Disaccharides, 'two sugars', are formed when twomonosaccharides are joined together and a molecule of water lost. Polysaccharides, 'manysugars', are long chains or polymers of sugar sub-units.

Lipids. non-polar (charge not separated) hydrophobic (water-hating) molecules. fats and oils store energyo phospholipids are essential components of membranes. steroids (hormones and vitamins) are made from lipids

Lipids are made up of C, H and O. The sub-units are fatty acids, both unsaturated (one ormore double carbon bonds) and saturated (all single carbon bonds, maximum possiblehydrogen atoms in the molecule). Double bonds cause permanent kinks or bends in the fattyacid chain. Mono-unsaturated fats have only one double bond, while polyunsaturated fattyacids have two or more double bonds. The more double bonds, the more bends or kinks in

the chain. This means the molecules cannot pack tightly together, and so space is leftbetween molecules. This is what gives membranes their permeability.

Compound lipids can also contain phosphorus and nitrogen. Phospholipids are hydrophilic(water-loving) at the phosphorus end and hydrophobic at the lipid end.

Basic structures of carbohydrates and lipidsCarbohydrates

@@€monosaccharide disaccharide

Lipidsthreemoleculesof fatty

,, acids

\'fatty acid

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polysaccharides

The Leading Edge - VCE Biology

Write definitions for the following words:polymers

monosaccharidesdisaccharidespolysaccharides

hydrophobichydrophilicphospholipids

unsaturatedsaturatedfatty acids

Proteins. 20 common amino acid sub-units. enzymes are catalysts (speed up the rates of reactions without being a part of the

reaction itself) for cellular reactions. hormones communicate information around the body. carrier molecules such as haemoglobin. form channels in membranes. also involved in the storage and transport of other molecules within and between cells

All proteins contain C, H, O and N. Some also contain phosphorus, sulfur or other elements.The protein sub-units are called amino acids. The bonds between amino acids are calledpeptide bonds, and proteins are also called polypeptides.There are four levels describing the structure of proteins:

. Primary - Ihe actual sequence of amino acids

. Seco ndary - pleating or coiling of the chain held together by hydrogen bonds betweendifferent amino acids

. Tertia4T - folding into a three-dimensional shape, usually globular or fibrous

. Quaternary - when two or more polypeptide chains join together to make a complexmolecule.

Nucleic acidso gen€tic material of all organisms. DNA - deoxyribonucleic acid, carries 'instructions' for building proteins

. RNA - ribonucleic acid, involved in polypeptide synthesis.

The sub-units of nucleic acids are nucleotides. There are only five different nucleotides in

nucleic acids, and they are distinguished by their bases - adenine (A), cytosine (C), guanine(G), thymine (T) and uracil (U). Adenine, cytosine and guanine are found in both DNA andRNA. Thymine is found only in DNA, and uracil is found only in RNA.

ln DNA, sequences of bases are called genes. Multiple genes are carried in chains calledchromosomes. The nucleotides are organised into triplet codes or codons, which translateinto amino acids. The sequence of these amino acids determines the protein that issynthesised. The proteins then determine all inherited characteristics of the organism.

. DNA nucleotides join in chains with distinctive ends because each nucleotide has aphosphate group, a five-carbon sugar and one of the following nitrogen bases:

o purines - double-ring baseso ff - adeniner G - guanine

. pyrimidines - single-ring baseso | - thymineo Q - cYtosine

Complementary base pairing between A-T (double hydrogen bond) and G-C (triplehydrogen bond) forms the 'rungs' of the 'twisted ladder' appearance of the double helix.

An organism's genome contains all of its genes. The proteome is the entire complement ofstructural and functional proteins that are coded for by the genome.

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The Leading Edge - VCE Biology

Basic structure of proteins and nucleic acids

Proteins Nucleic acids

nucleotide_"__-l_ _

phosphate Q

sugar @I bases

(four types)

AIe FrIlCIr F.r,l

I amino acid

A subunitsol\

Write definitions for the following words:amino acidenzymescatalystspeptide bondspolypeptides

DNARNAnucleotidesbaseschromosomes

triplet codescodonsgenesgenomeproteome

anic molecule summa

TypeMain

elements Sub-units Complex product Example

Carbohydrate c,H,o saccharides polysaccharides sucrose

Lipid c,H,o fatty acidsand oils

saturated fats vegetable oil

Protein C,H,O,N amino acids polypeptide enzyme

Nucleic acid C,H,O,N,P nucleotides often genes DNA

Organelles and membranesMembranes. Possibly the most important part of a cell, the plasma membrane (also called the cell

membrane) selectively regulates movement of substances into and out of a cell. Mostorganelles are also enveloped in membranes.

. Membranes create separate compartments within the cell, keeping different functioningcentres and substances apart and controlling the movement of substances betweenthe different compartments.

. Many chemical reactions occur in, on or around membranes.

. Plasma membranes are involved in cell recognition and intercellular communication,both electrically and chemically

. Plasma membranes consist of a bilayer (double layer) of phospholipids with theirhydrophobic ends together (see diagram on page 14), as well as carbohydrates andproteins. The bilayer of phospholipids is impermeable to water-soluble or polarsubstances

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VCE Biologlt

glycoProtein -recognition

.(

Plasma membranecarbohydrates cell adhesion

proteinpump protein -active transport

phospholiPidbilayer

m;il p.,t,u"lofcell I diffusion

and osmosis

cholesterol

Most of the different types of molecules within a bilayer can move around to a varyingextent. The fluid-mosaic model explains this movement.Gholesterol is between the layers of phospholipids, making the structure more stableby preventing the molecules from moving around too much. Cholesterol prevents themembrane from breaking down and decreases permeability to polar molecules. Onlyfound in animal cells.

of a cell

Cellwall Permeable structure providing support to cell; only in plants (cellulose), someprotists, prokaryotes (murein) and fungi (chitin).

Organelle FunctionCentrioles Microtubules involved in separating chromosomes during cell division.Chloroplast Contains chlorophyll and is the site of photosynthesis.

Cytoplasm Contents of the cell apart from the nucleus.

Cytosol Fluid component of the cytoplasm.

Endoplasmicreticulum(ER)

Membrane network linked with plasma membrane and other membrane-boundorganelles. Produces, packages, stores and transports materials within the cell.cqn be rough (associated with ribosomes, RER)or smooth (without ribosomes,SER). Abundant in cells that actively synthesise and secrete enzymes.

Golgiapparatus

Linked to endoplasmic reticulum. synthesises and packages proteins intovesicles.

Lysosomes Vesicles containing strong enzymes that break down cell debris and foreignmatter.

Mitochondria Site of cellular respiration to release energy for the cell to use.

Nucleus Double-membrane bound organelle with pores allowing movement between thenucleus and cytoplasm. Contains genetic material (DNA).

Plasmamembrane

Bilayer of phospholipids controlling movement of substances into and out of thecell. Also responsible for recognition, adhesion and chemical communicationbetween cells.

Ribosomes Synthesise proteins; often associated with endoplasmic reticulum.

Tonoplast Vacuole membrane in plants. Regulates movement of substances into and out ofvacuole.

VacuolesMembrane-bound fluid spaces, varying in size and number depending on celltype. Provide turgidity (support) in plants, or involved with digestion and waterbalance.

Vesicles Membrane-bou nd organelles involved in transportation of substances.

I4

Write definitions for the following words:phospholipid bilayerfluid-mosaic model

cholesterolorganelle

The Leading Edge - VCE Biolog

Synthesis of biomolecules. The largest organelle in the cell is usually the nucleus, and most cells only have one.

Some cells, such as red blood cells, lose their nucleus after maturity. The nucleus hasa double-layered nuclear envelope containing many nuclear pores through whichmany substances can pass.

. The nucleolus is the only visible structure within the nucleus in a non-dividing cell.Nucleoli are rich in RNA and proteins and are the site of ribosomal RNA (rRNA)synthesis. There can be more than one nucleolus in the nucleus.

. The instructions for building enzymes and other proteins are in the DNA. This meansall cell maintenance and functions are regulated and controlled by the DNA in thenucleus. Messenger RNA (mRNA)and rRNA, produced in the nucleus, pass outthrough the nuclear pores into the cytoplasm.

. mRNA and rRNA bind with ribosomes and start protein synthesis. Amino acids areadded one at a time in the sequence outlined by the mRNA translation of the DNA.Enzymes produced by free ribosomes usually function within the cytoplasm.Ribosomes bound to endoplasmic reticulum, RER, usually produce proteins that areused in membranes or are packaged into vesicles for export from the cell.

Packaging and transport of biomolecules. Fats, phospholipids and steroids are synthesised by SER. SER is abundant in the cells

of steroid-secreting organs such as the testes and adrenal gland.. The Golgi apparatus also packages polysaccharides and creates lysosomes, which are

membrane-bound vesicles budded off the Golgi apparatus. They contain enzymes thatare used to break down debris in the cell. Reusable material diffuses back into thecytoplasm from the lysosomes, while unwanted material is expelled by exocytosis.

Gonstruction, packaging

ER is composed of interconnecting cisternae (membrane sacs) and branching tubes that are attached to the nuclearmembrane. The internal cavity, the lumen, contains enzymes and proteins that metabolise, synthesise and process othermolecules. They ensure that proteins have the correct 3-D shape and regulate the calcium concentration in the cytoplism.As the proteins are synthesised, they pass into the lumen and then on to the Golgi apparatus. Here they are furthermodified; carbohydrates and proteins are added to form glycoproteins.

The proteins are then packaged into vesicles, which fuse with the plasma membrane and release their contents into theintercellular space by exocytosis.

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