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Chapter 4 Genes and DNA. Section 1+2 Pages 84-101. What does DNA look like?. Pieces of the Puzzle: DNA must be able to give instructions for building and maintaining cells. DNA must be able to be copied each time a cell divides, so each cell contains identical genes. .

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chapter 4 genes and dna

Chapter 4 Genes and DNA

Section 1+2

Pages 84-101

what does dna look like
What does DNA look like?
  • Pieces of the Puzzle:
  • DNA must be able to give instructions for building and maintaining cells.
  • DNA must be able to be copied each time a cell divides, so each cell contains identical genes.
nucleotides subunits of dna
Nucleotides: Subunits of DNA
  • A nucleotide consists of a sugar, a phosphate, and a base. Nucleotides are identical except for their base.
  • There are 4 bases: Adenine, Thymine, Guanine, and Cytosine
  • All four bases have a different shape.
chargaff s rules
Chargaff’s Rules
  • Guanine and Cytosine always occur in equal amounts in DNA, as do Adenine and Thymine
franklin s discovery
Franklin’s Discovery
  • Used X Ray diffraction to make images of DNA molecules
  • Suggested the spiral shape of DNA
watson and crick s model
Watson and Crick’s Model
  • After seeing Franklin’s image, Watson and Crick concluded that DNA must look like a long, twisted ladder.
  • This helped explain how DNA is copied and how it functions in the cell.
dna s double structure
DNA’s Double Structure
  • Double Helix, two sides of the ladder are made of alternating sugar parts and phosphate parts.
  • The rungs of the ladder are made of a pair of bases:



animated dna
Animated DNA
making copies of dna
Making Copies of DNA
  • Pairing the bases allows the cell to replicate or make copies of DNA
  • The pairs are complementary since they always pair A-T and G-C
how are copies made
How are copies made?
  • During replication, a DNA molecule is split down the middle, where bases meet.
  • The bases on each side of the molecule are used as a pattern for the new strand.
  • As the bases on the original molecule are exposed, complementary nucleotides are added to each side of the ladder.
  • Two DNA molecules are formed.
  • Half of each of the molecules is old DNA, half is the new DNA
unraveling dna
Unraveling DNA
  • DNA is often wound around proteins, coiled into strands, and bundled up even more.
  • Cell’s without a nucleus the DNA forms loose loops within the cell.
  • Cell’s with a nucleus the DNA and proteins are bundled into chromosomes.
when are copies made
When are copies made?
  • DNA is copied every time a cell divides.
  • The job of unwinding, copying and re-winding the DNA is done by proteins within the cell.
unraveling dna1
Unraveling DNA
  • The structure of DNA allows it to hold information.
  • The order of the bases is the code that carries the information.
  • A gene consists of a string of nucleotides that give the cell information about how to make a specific trait.
  • Humans have over 30,000 genes.
  • 2003 Human Genome Project
unraveling dna quiz
Unraveling DNA- Quiz
  • Where is the DNA in your cells?
  • How does so much DNA fit into the nucleus?
  • What is the name for strands of DNA wound around proteins?
  • When do chromosomes become visible in cells?
  • What are chromatids?
  • In the nucleus
  • It is coiled up tightly around proteins
  • Chromatin
  • When the cell is about to divide
  • Two identical copies of a chromosome that is about to divide
genes and proteins
Genes and Proteins
  • DNA code is read like a book, from one end to the other and in one direction.
  • Bases form the alphabet of the code.
  • Groups of 3 bases are code for the amino acid profile. (example: AGC)
  • A long string of amino acids forms a protein.
  • Each gene is usually a set of instructions for making a protein.
proteins and traits
Proteins and Traits
  • Proteins are found throughout cells and cause most of the differences that you see among organisms.
  • Proteins act as chemical triggers and messengers for many processes within the cell.
  • A single organism may have thousands of genes that code for thousands of proteins.
help from rna
Help from RNA
  • RNA (ribonucleic acid) a molecule that is present in all living cells and that plays a role in protein production
  • Helps in the process of changing the DNA code into proteins
making of a protein
Making of a Protein
  • Step 1: A copy is made of one side of the DNA segment where a particular gene is located. This copy is transferred to the cytoplasm.
making of a protein1
Making of a Protein
  • Step 2: This mirror like copy of a DNA segment is called messenger RNA (mRNA).

Messenger RNA copies the coded message from DNA in the nucleus , and carries the message to the ribosome in the cytoplasm.

making of a protein2
Making of a Protein
  • Step 3: Each group of three bases on the mRNA segment codes for one amino acid.
making of a protein3
Making of a Protein
  • Step 4: The mRNA segment is fed through the ribosome. A ribosome is a cell organelle composed of RNA and protein.
making of a protein4
Making of a Protein
  • Step 5: Molecules of

transfer RNA (tRNA) deliver amino acids from the cytoplasm to the ribosome.

Transfer RNA (tRNA) transfers amino acids to the ribosome and adds them to the growing protein.

making of a protein5
Making of a Protein
  • Step 6: The amino acids

are dropped off

at the ribosome.

making of a protein6
Making of a Protein
  • Step 7: The amino acids are joined to make a protein. Usually, one protein is produced for each gene.
animated mrna
Animated mRNA
how is rna different from dna
How is RNA different from DNA?
  • RNA: one strand

contains uracil instead of thymine

A, G, C, U

  • DNA: two strands

A, G, C, T

changes in genes
Changes in Genes
  • Mutation: a change in the nucleotide-base sequence of a gene or DNA molecule
  • Either deletion, insertion or substitution
  • Causes an improved trait, no change or harmful trait
  • If the mutation occurs on the sex cells, the mutation can be passed to the next generation
  • Mutations happen often
  • Mutagens are any physical or chemical agent that can cause the mutation (examples: UV radiation, X rays, cigarette smoke)
  • Examples are Cystic Fibrosis, Sickle Cell Anemia, Hemophilia, Down Syndrome
example of substitution
Example of Substitution
  • Sickle Cell Anemia- affects red blood cells. When Valine is substituted for glutamic acid in a blood protein. The change in shape isn’t good for the cell to carry oxygen and clot in vessel (very painful).
  • Genetic Engineering: Manipulate individual genes to create new products, such as foods, drug or fabrics
  • Genetic Identification: DNA is your unique fingerprint, only identical twins share DNA

Clone: a new organism that has an exact copy of another organism’s genes.

  • Selective breeding: A technique to produce offspring with desirable traits.

Inbreeding: cross two genetically similar (male/female plump turkey)

Hybridization: cross two genetically different (mcintosh and red delicious apple to get an empire)

web sites
Web sites…..
  • DNA and Genetics:
  • Genetics: