chapter 4 genes and dna
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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. . - PowerPoint PPT PresentationTRANSCRIPT
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Chapter 4 Genes and DNASection 1+2
Pages 84-101
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What does DNA look like?• Pieces of the Puzzle: 1. DNA must be able to
give instructions for building and maintaining cells.
2. DNA must be able to be copied each time a cell divides, so each cell contains identical genes.
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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.
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Chargaff’s Rules• Guanine and Cytosine
always occur in equal amounts in DNA, as do Adenine and Thymine
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Franklin’s Discovery• Used X Ray diffraction
to make images of DNA molecules
• Suggested the spiral shape of DNA
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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.
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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:
Adenine-ThymineGuanine-Cytosine
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Animated DNA
• http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/animation__dna_replication__quiz_1_.html
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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
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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
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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.
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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.
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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
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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
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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.
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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.
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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
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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.
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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.
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Making of a Protein• Step 3: Each group of
three bases on the mRNA segment codes for one amino acid.
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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.
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Making of a Protein• Step 5: Molecules oftransfer 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.
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Making of a Protein• Step 6: The amino acidsare dropped offat the ribosome.
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Making of a Protein• Step 7: The amino acids
are joined to make a protein. Usually, one protein is produced for each gene.
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Animated mRNA
• http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/animation__mrna_synthesis__transcription___quiz_1_.html
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How is RNA different from DNA?
• RNA: one strandcontains uracil instead of thymine A, G, C, U
• DNA: two strands A, G, C, T
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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
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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).
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Genetics• 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 DNAClone: 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)
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Web sites…..• DNA and Genetics:• http://www.pbs.org/wnet/dna/episode1/index.html#• http://www.pbs.org/wgbh/aso/tryit/dna/• http://learn.genetics.utah.edu/content/begin/dna/• http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html• http://www.mesacc.edu/~tinhw34501/psquare.pdf• http://www.nature.ca/genome/05/051/0511/0511_m205_e.cfm• http://www.pbs.org/wgbh/nova/body/sequence-DNA-for-yourself.html• http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html • Genetics:• http://pbskids.org/dragonflytv/games/game_dogbreeding.html• http://www.worldwildlife.org/sites/inner-animal/index.html• http://anthro.palomar.edu/mendel/mendel_2.htm• http://www.athro.com/evo/gen/punexam.html• http://www2.edc.org/weblabs/Punnett/punnettsquares.html• http://biology.clc.uc.edu/courses/bio105/geneprob.htm• http://www.cellsproject.org/examples/sc/page23.html• http://glencoe.mcgraw-hill.com/sites/0078778066/student_view0/chapter5/math_practice.html• http://anthro.palomar.edu/mendel/mendel_1.htm• http://www.biology.arizona.edu/Mendelian_genetics/mendelian_genetics.html• http://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel1.htm• http://www.pbs.org/wgbh/nova/body/cracking-the-code-of-life.html