Discovering DNA• When did we first know that there was a nucleus in cells that contained large molecules called nucleic acids? • mid-1800s• By the 1950s we still were not sure how the nucleic acids and DNA were arranged.
Rosalind Franklin discovered that DNA is 2 chains ofmolecules in a spiral form.
Watson and Crick further studied the DNA model.
Watson and Crick discovered that each side of theladder is make of a sugar-phosphate molecule.
GEnes• Most of your characteristics, such as the colour of your hair, your height, and how things taste to you, depend on the kinds of proteins your cells make.• DNA in your cells stores the instructions for making these proteins.• Proteins build cells and tissues or work as enzymes.• The instructions for making a specific protein are found in a gene.
GEnes• A gene is a section of DNA on a chromosome.• A chromosome contains 100’s of genes.
GEnes• Proteins are made of amino acids linking together.• The code for making a protein is found...• .......in a gene.• The gene determines the order of the hundreds or thousand of amino acids that link together.• If you change the order, you make a different protein or nothing at all.
GEnes• Genes are found in the nucleus, but proteins are made on ribosomes in the cytoplasm.• How does the code for a protein make it out of the nucleus to a ribosome?• The codes for making proteins are carried from the nucleus to the ribosome by another type of nucleic acid called ribonucleic acid, RNA.
RNA - Ribonucleic Acid RNA is made in the nucleus on a DNA pattern but is different from DNA. If DNA is like a ladder, RNA is like a ladder that has all its rungs cut in half.
DNA vs RNA nitrogen sugar shape basesDNA AGCT deoxyribose ladderRNA A G C U* ribose ladder cut in half *U - uracil
Transcription copying a DNA to make RNA1 1. An enzyme splits a DNA molecule, so that a gene can be copied. The gene is the instructions for how to make a protein.
Transcriptioncopying a DNA to make RNA 2. The free floating nitrogen bases in the 2 nucleus match with a nitrogen base on the split DNA. The partnering is the same as when DNA is copied except that Adenine matches with Uracil.
Transcriptioncopying a DNA to make RNA 3 3. The nitrogen bases pair up on the split DNA temporarily until a complete gene is copied.
Transcriptioncopying a DNA to make RNA 4. The newly made mRNA will now detach from the DNA and leave 4 the nucleus.
3 types of RNA mRNA rRNA tRNAmessenger ribosomal transfertravel out of bring amino acids nucleus to make up ribosomes to ribosomes ribosome
Translation - RNA to Protein• Protein production begins when mRNA moves into the cytoplasm. There, ribosomes attach to it.• Ribosomes are made of rRNA.• Transfer RNA molecules in the cytoplasm bring amino acids to these ribosomes.
Translation - RNA to Protein• Inside the ribosomes, 3 nitrogen bases on the mRNA temporarily match with 3 nitrogen bases on the tRNA.• The same thing happens for the mRNA and another tRNA molecules.• The amino acids that are attached to the two tRNA molecules bond.• This is the beginning of a protein.
Translation - RNA to Protein• The code carried on the mRNA directs the order in which the amino acids bond.• After a tRNA molecule has lost its amino acid, it can move about the cytoplasm and pick up another amino acids just like the first one.• The ribosome moves along the mRNA.• New tRNA molecules with amino acids match up and add amino acids to the protein molecule.
3 nitrogenbases onmRNAtemporarilymatch to 3bases on thetRNA.
The amino acids that are attached tothe tRNA bond, beginning to form theprotein.
Controlling Genes• In many-celled organisms, each cell uses only some of the thousands of genes that it has to make proteins.• Genes that code for muscle proteins will not be used in nerve cells.
Controlling Genes• Cells must be able to control the genes by turning some off and some on.• This is done in different ways:• DNA is twisted so tightly that no RNA can be made.• Chemicals bind to the DNA so that it cannot be used.
Mutations• If DNA is not copied correctly the proteins might not be made correctly.• Mutations - any permanent change in the DNA sequence of a gene or chromosome of a cell• Examples: • cells receive an extra or are missing a chromosome • outside factors: X rays, sunlight, some chemicals
REsults of Mutations• A mutation might or might not be life threatening.• If the mutation occurs in the sex cell then all the cells of the new organism will contain the mutation.• Most mutations are very harmful, but some can be beneficial.• Beneficial?• A plant with a mutation might cause it to produce a chemical that certain insects avoid, insects will not eat the plant.