Academic Biology Review

Chapters 6-11

Gregor Mendel……..the…..MAN!

Chapter 6

• Gregor Mendel discovered that inheritance was particulate and not blended. He called the units of inheritance “genes.”

• He investigated heredity using pea plants. With these plants he discovered several principles of heredity, including “independent assortment.”

• Independent assortment is when the chromosomes which have genes on them line up in the cell during meiosis. This process ensures you get one allele from your father and one allele from your mother for each gene, but the combinations of possible alleles for the entire genotype are extremely high (2^46).

Punnett Squares Yo!

• Punnett squares were developed to determine the possible genotypes (allele combinations) and phenotypes (expressed traits) between two mating individuals.

• Each parent has two alleles. The size of the letter indicates whether it is dominant or recessive. When there are two dominant alleles together, or a dominant and a recessive together, the phenotype is dominant. If there are two recessives together, the phenotype is recessive.

Punnett Sqares

• When one trait is looked at, it is called a monohybrid cross. For two traits, a dihybrid cross, and so on (tri-,etc.).

• Treat the area above the punnett square as the father’s genotype and the left as the mother’s genotype. Put an allele over each column and next to each row. Then, fill the squares out as you would a multiplication table.

A monohybrid cross in action!

Punnett Sqares

• Each square represents one possibility. When there are four present, each square is ¼ of the possibilities.

• When you convert these to probabilities, the total of all the numbers should add up to the number of squares. For example, when you have a normal experimental cross (two heterozygotes in the F2 generation), the probabilities are 1:2:1 which add up to four. The first number represents the number of homozygous dominant squares, the second represents the heterozygote squares, and the last number represents homozygous recessive squares.

• Remember, there are probabilities for both the genotype and the phenotype.

Different Types of Crosses

• When the genotype of an organism is unknown, it is bred with a homozygous recessive individual and the phenotype of the offspring is observed. This is called a test cross.

• During a normal experimental cross, a homozygous dominant individual and a homozygous recessive individual are mated to produce all heterozygotes in the F1 generation. Then two heterozygotes breed and produce another generation called the F2 generation.

Genomes, Karyotypes, etc.

• The totality of someone’s genetic material is their genome.

• A picture of someone’s genome is called a karyotype.

• A special tree used to track genetic illnesses in humans is called a pedigree.

Macromolecule Review

• Four types of macromolecules:

-Carbohydrates (sugars)-have suffix

-ose

-Lipids (fats)-have prefix glyc-

-Proteins (made from amino acids)

have the suffix –ase

-Nucleic acids-DNA or RNA

The DNA double helix!

Chapter 7

• Genes are located within DNA (Deoxyribonucleic acid). DNA is wound up in chromosomes and in eukaryotes is located in the nucleus.

• DNA is formed from a deoxyribose sugar, inorganic phosphate, and a nitrogenous base.

• There are two strands in DNA which attach with a hydrogen bond, which is very weak.

• The nitrogenous bases, which code for proteins are: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).

Watson and Crick, the discoverers of the shape of DNA-A twisted ladder, or Double Helix!

Complimentary Base Pairing

• DNA is double stranded because of complimentary base pairing. Complimentary base pairing occurs between A and T, G and C.

• Do not confuse complimentary base pairing with purine (A and G) and pyrimidine bases (C and T). One purine binds with one pyrimidine.

DNA Replication

• During DNA replication (before cell division), DNA is split apart by an enzyme called helicase, and then on each strand, another enzyme called DNA polymerase runs down the strands and puts the complimentary base on each base. At the end of this process, there are two DNA molecules, each has one strand of the parent molecule, and one strand of new material.

THE CENTRAL DOGMA OF MOLECULAR BIOLOGY

Chapter 8

• Protein synthesis is when DNA is read and proteins are produced as a result.

• Protein synthesis starts out similar to DNA replication, but with some differences. First, only a portion of the DNA chain splits apart, and a new enzyme, RNA Polymerase runs down one side of the DNA molecule to produce a complimentary strand out of RNA pieces.

• RNA is Ribonucleic Acid, so named because it has a ribose sugar instead of a deoxyribose sugar. Also, the base T from DNA is replaced with Uracil (U). RNA is single stranded.

Transcription

• When mRNA is made from the DNA strands, it is called transcription. Transcription occurs in the nucleus and is followed by…..

mRNA Splicing

• The new mRNA contains both introns (non-expressed portions) and exons (expressed portions). The introns are removed and the exons are “spliced” back together. This also happens within the nucleus.

• From here, the mRNA leaves the nucleus and enters the cytoplasm where….

Translation

• mRNA is translated using ribosomes and tRNA (transfer RNA). A ribosome forms around mRNA and reads it like a typewriter does. As it moves down the mRNA, tRNA molecules (which are RNA with a sequence of three bases called an anti-codon, and an amino acid on the top) move into the ribosome and complementarily bind with a three base sequence in the mRNA called a codon.

• The amino acids are formed in a chain which is then processed and made into a functional and/or a structural protein.

Mutations

• A mutation is the change in the DNA of an organism.

• If this change does not change the amino acid that would have been produced, it is called a “silent mutation.”

• If this change causes a new base to be inserted or an old one to be taken out, it affects the reading frame of the ribosome during translation, the mutation is a “fram-shift mutation.”

Mutations

• There are four general mutation types you need to know:– Addition – A base or bases is inserted into the

sequence.– Deletion – A base or bases is deleted from the

sequence.– Duplication – A sequence of bases or one

base are repeated in the sequence.– Translocation – A segment of DNA breaks off

and reattaches to another chromosome.

Crossing Over

• When chromosomes line up at the beginning of meiosis (Prophase I), there is a possibility that they will exchange genetic material. This is called crossing over.

• Crossing over can produce new combinations of alleles and this confused Mendel when he saw it so much, that he thought it was an abberation and he left it out of his finished work.

CROSSING OVER IN ACTION!

Cancer

• Mutations can be caused by chemicals called mutagens.

• Mutagens that cause cancer are called carcinogens, and the mutations themselves are referred to as oncogene mutations.

• Remember, cancer is when cells divide but cannot die. They run rampant and usually result in death.

WHAT MUTAGENS DON’T LEAD TO

Protein regulation

• Not all genes are activated in a cell at one time. Only specific genes are needed.

• Repressor proteins bind to the DNA and prevent DNA polymerase from attaching to the promoter region.

• When a molecule that signals the production of a protein hits the repressor, it changes shape and falls off the DNA, allowing it to be copied.

Repressor Proteins in Action

Chapter 9 (brief)

• Biotechnology is the use of technology to alter what is natural in the biological world, usually to make products that benefit man.

• Oldest form of biotechnology is artificial selection (selective breeding).

• New forms use genetic engineering to go into the cell and alter the genes.

• This technology has raised many ethical considerations because of how we alter nature, or ourselves in the process.

TREE OF LIFE-Based on cellular structures and genetics.

Chapter 10

• The Theory of Evolution is not “just a theory.” It is a set of hypotheses, inferences, facts, and laws which explain among other things, animal diversity.

• Evolution is not a new concept, but it rose above being a philosophical idea through the work of Charles Darwin and Alfred Russel Wallace who codiscovered Natural Selection.

Darwin and Wallace

Evidence for Evolution

• Comparative anatomy.

• Similar genetic code.

• Similar proteins.

• Similarities in embryos.

• Biogeography.

• Fossils-subject of chapter 11.

Evolution

• For evolution (change in gene/allele frequencies in a population ) to occur, four things are needed:

1. Genetic variation.2. Limited resources and overproduction of offspring.3. Competition for resources.4. Differential survival and reproduction in individuals with

a beneficial trait in the population.5. More offspring of organisms who can get the most

resources are left, and these offspring carry the genetic benefits of their parents. This is what evolution is.

Evolution

• Microevolution is what was discussed using gene frequency changes in the population. The ultimate expression of this change is “speciation,” the emergence of a new species.

• Macroevolution is change above the species level. This is shown in the fossil record.

Chapter 11

• Need to remember the order of periods, eras, and eons which geologic time is subdivided into (see page 5 of handout).

• An easy way to remember the order of periods in the Paleozoic is COSDMPP. Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian.

Development of Life

• The overall trend of life is simple complex.• Easy way to remember trends: microbes

plants/animals invertebrates vertebrates jawless fish jawed fish amphibians reptiles birds and mammals.

• Major mass extinctions: Permian, Cretaceous, Quaternary (last ice age).

• Also remember, at least two supercontinents (Rodinia in Proterozoic and Pangaea in late Paleozoic/middle Mesozoic.