9. 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.
27. 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.
28. GEnes
• A gene is a section of
DNA on a chromosome.
• A chromosome contains
100’s of genes.
29. 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.
30. 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.
31. 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.
32. DNA vs RNA
nitrogen
sugar shape
bases
DNA AGCT deoxyribose ladder
RNA A G C U* ribose ladder cut in half
*U - uracil
33. Transcription
copying a DNA to make RNA
1 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.
34. Transcription
copying 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.
35. Transcription
copying a DNA to make RNA
3
3. The nitrogen bases
pair up on the split DNA
temporarily until a
complete gene is copied.
36. Transcription
copying a DNA to make RNA
4. The newly made
mRNA will now detach
from the DNA and leave
4 the nucleus.
37.
38.
39. 3 types of RNA
mRNA rRNA tRNA
messenger ribosomal transfer
travel out of
bring amino acids
nucleus to make up ribosomes
to ribosomes
ribosome
40. 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.
41. 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.
42. 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.
48. The amino acids that are attached to
the tRNA bond, beginning to form the
protein.
49.
50.
51.
52. 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.
53. 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.
54. 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
56. 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.
