Chapter 4 Genes and DNASection 1+2

Pages 84-101

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.

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• Guanine and Cytosine

always occur in equal amounts in DNA, as do Adenine and Thymine

Franklin’s Discovery• Used X Ray diffraction

to make images of DNA molecules

• Suggested the spiral shape of DNA

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• 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

Animated DNA

• http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/animation__dna_replication__quiz_1_.html

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? • 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• 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?• 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 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• 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• 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 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• 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• 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 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 Protein• Step 3: Each group of

three bases on the mRNA segment codes for one amino acid.

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 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.

Making of a Protein• Step 6: The amino acidsare dropped offat the ribosome.

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

• http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/animation__mrna_synthesis__transcription___quiz_1_.html

How is RNA different from DNA?

• RNA: one strandcontains uracil instead of thymine A, G, C, U

• DNA: two strands A, G, C, T

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 • 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).

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)

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