Unit 5 Review

DNA, Protein Synthesis, Mutations

Griffith

• Bacterial Transformation

Hershey and Chase• DNA is the hereditary material

Watson, Crick, Franklin

• Franklin: X-Ray crystallography• Image of DNA

• Watson and Crick: Built the 3D Model of DNA

Chargaff

A-TC-G

Nucleic Acids

• Polymers• Made of nucleotides

– 5-Carbon Sugar– Phosphate Group– Nitrogen Base

• The bases are the INFORMATIONAL part of DNA!!

DNA vs. RNA

DNA• Usually double stranded

(some viruses have single stranded DNA)

• Stores Genetic Info• 2 strands held together by

weak H bonds• THYMINE• Deoxyribose sugar

RNA• Single stranded

– mRNA – carries instructions for making proteins-transmits genetic info

– tRNA – transfers AA– rRNA – assembles AA

• URACIL• Ribose sugar

BOTH are nucleic acidsBOTH are built from nucleotides

BOTH have A, C, and G

• DNA has to be replicated (copied) before a cell divides

• DNA is replicated during the S phase (or synthesis phase) of the cell cycle

• New cells will need identical DNA strands

Replication Facts

Enzymes involved with Dna replication

Helicase – unzips the DNA helix

Dna Polymerase- synthesizes the new DNA strands by adding DNA nucleotides

Ligase- joins okazaki fragments

Protein Synthesis

• Anabolic• Proteins are built of Amino Acids• Genes code for proteins

– Transcription (RNA synthesis)– Translation (assembling amino acids into proteins)

• Are all proteins the same size? Why or why not?

Genetic Code• UNIVERSAL

– Although living creatures are diverse and unique the components of their genetic code are the same.

• Suggests a common ancestor• Specific order of nitrogen bases (or

nucleotides) determines what proteins are made, and therefore, what traits are expressed.

Codon Chart = Universal

Gene Expression

• Gene expression is a regulated process– Gene regulation results in a conservation of cell

resources• Even though ALL of your cells have the same

genes, liver cells express different genes than cardiac muscle cells, resulting in cell differentiation

Lac Operon

• Inducible system• Lactase is only produced in the presence of

lactose• So if no lactose, no lactase produced…• Gene regulation results in conservation of cell

resources

Genes code for proteins

• But not ALL of a gene is expressed• Only EXONS code for proteins• INTRONS are removed by RNA splicing

Mutations

• Heritable mutations occur in gametes• Somatic mutations cannot be passed down

Types of Mutations – mistakesa) Point Mutations – effects a single gene

i. Substitution-Missense-Nonsense

ii. Frameshift-Insertion-Deletion

b) Chromosomal mutations – most drastic, change in structure or # of chromosomes (affects many genes)many are due to non-disjunction.

The Effects of Point Mutations

► A point mutation is a change in a single base pair in DNA.– A change in a single nitrogenous base can change the entire structure of a

protein because a change in a single amino acid can affect the shape of the protein. (SUBSTITUTION)

Gene Mutations

Normal

Point mutation

mRNA

Protein Stop

Stop

mRNA

Protein

Replace G with A

Frameshift Mutations

► What would happen if a single base were lost from a DNA strand?► A mutation in which a single base is added or deleted from DNA is

called a frameshift mutation because it shifts the reading of codons by one base.– As a result, every codon after the deleted base would be different.

Gene Mutations

mRNA

Protein

Deletion of U

• Mutations can be – Good– Bad– Have no effect (silent)

• Fixed by enzymes• Result in same AA• Occur in a non-coding region of DNA (such as an intron)• Occur in a gene that is not expressed(such as a

recessive trait)

Recombinant DNA and Biotechnology

• Biotechnology• Genetic Engineering (Gene Therapy)• Recombinant DNA-the genes of an organism are changed by

recombining its DNA with the DNA (or genes) from another organism.

• Purpose- By inserting genes into the genome of an organism, the scientist can induce the organism to produce a protein it does not normally produce. This can help improve the quality of life for that organism.

• Uses-bacteria that carry recombinant DNA can be released into the environment to increase the fertility of the soil, serve as an insecticide, or relieve pollution.

• How it works-Restriction enzymes catalyze the opening of a DNA molecule at a “restricted” point, regardless of the DNA's source. Certain restriction enzymes leave dangling ends of DNA molecules at the point where the DNA is open. Foreign DNA can then be combined with the carrier DNA at this point. An enzyme called DNA ligase is used to form a permanent link between the dangling ends of the DNA molecules at the point of union (Figure 1).

Genetic Engineering

The production of a recombined bacterium using a gene from a foreign donor and the synthesis of

protein encoded by the recombinant DNA molecule.

The production of a recombined bacterium using a gene from a foreign donor and the synthesis of

protein encoded by the recombinant DNA molecule.

Techniques used to study genomes:

• Genetic modification – involves scientists identifying and isolating genes that code for specific traits, and then manipulating those factors that affect the genes’ expression. – “GMOs” (genetically modified organisms) may have the genes of

another organism inserted to add a desired trait. (For example, insect resistant GM cotton uses a gene from a naturally occurring soil bacterium to provide it with built-in insect protection.)

– Gene therapy is a form of genetic modification used to treat patients with genetic disorders. In theory, a patient with a defective gene could have it replaced with a working version of the gene.

Techniques used to study genomes:

• DNA fingerprinting- is a process in which a small sample of human DNA is cut with a restriction enzyme. The DNA fragments are separated according to size using gel electrophoresis and DNA probes. This creates a series of bands based on the size of the persons DNA fragments. The banding pattern created is unique, with the exception of identical twins. Banding patterns produced by two samples can be compared to establish whether the sources are related (paternity case) or come from the same person (crime scene.) DNA fingerprinting is also valuable for identifying the genes that cause genetic disorders.

Think “Who stole the Cheese?”

Chromosomal analysis- involves using karyotypes to identify chromosomal mutations in which an individual has an extra chromosome or is missing a chromosome. These types of mutations are caused by nondisjunction during meiosis. Karyotypes can be used to identify the possible location of a gene or a genetic abnormality on a chromosome.