Unit 6- Genetic Expression

Macromolecule of DNA

Nucleic Acid

3 parts to a nucleotide

Phosphate group, pentose sugar, nitrogenous base

Purines

Double Ringed (A and G)

Nitrogenous Bases

Adenine, Guanine, Cytosine, Thymine, and URacil

Pyrimidines

Single Ringed (C, U, and T)

Pentose Sugar

Deoxyribose and Ribose

Antiparallel

Each strand runs in a different direction (5’ → 3’ or 3’ → 5’)

Complementary

Each base on one strand is joined to its partner base on the second through H-bonds (A=T, C=G)

Phosphodiester bonds

Phosphate group from one nucleotide linked to the pentose sugar of an adjacent nucleotide. Enzymes create these bonds via dehydration reactions.

Griffith’s Transformation Experiment (1928)

Bacterial cells carry information that can be transmitted to other cells, led scientists to know what cell components has this function.

Avery, MacLeod, and McCarthy Experiment (1944)

Evidence for DNA as the genetic material

Chargaff Experiment (1950)

Discovery of the 1:1 purine to pyrimidine ratio in a double- stranded DNA

Hershey and Chase (1952)

Viruses are made of two main parts (Nucleic Acid and DNA or RNA). Viruses inject their genetic material into cells and hijack the cellular machinery in order to reproduce.

Rosalind Franklin’s Work (1952)

Research team uses X-ray crystallography to visualize DNA structure

Watson and Crick’s Model (1953)

Used Chargaff’s data, photo 1 (from Franklin’s research team). Helped discovery Nitrogenous based are Purine and Pyrimidine.

Helicase

“Unwinds” double helix by breaking hydrogen bonds between base pairs`

Topoisomerase

Enzymes helps to relieve the strain of untwisting process by breaking, swiveling, and rejoining DNA strands

Primase

Builds a short RNA primer

DNA Polymerase II

Matches new nucleotides to exposed parent strand

DNA Polymerase I

Replaces RNA nucleotides from primers with DNA nucleotides, based on the complementary parent strand sequence

Origins of replication

Short stretches of DNA having a specific sequence of nucleotides (prokaryotes have only one, eukaryotes have hundreds or thousands)

Leading Strand

Synthesized faster due to need of only one primer for DNA polymerase

Lagging Strand

Synthesis rate lags behind leading strand because DNA polymerase must work along the template strand in the direction away from the replication fork, multiple primers necessary

Okazaki Fragments

Broken fragments due to DNA polymerase moving in the 5’ to 3’ direction

Initiation

Proteins bind to the origin of replication while helicase unwinds the DNA helix and two replication forks are formed at the origin of replication

Single Stranded Binding Proteins

Bind to the unpaired DNA strands to prevent them from rejoining until replication is completed

Elongation

Primase adds a primer sequence is added with complementary RNA nucleotides. DNA Polymerase III creates phosphodiester bonds in the new DNA backbone as it moves form the 5’ to 3’ direction on the growing strand

Termination

RNA primers are removed and replaced with new DNA nucleotides (DNA Polymerase I). DNA ligase seals any gaps in the strand with phosphodiester bonds

Pulse Chase Method

In 1958, two molecular biologists and geneticists named Matthew Meselson and Franklin Stahl used the pulse chase method to determine the semi- conservative nature of DNA replication.

Meselson and Stahl (Late 1950)

Verify that DNA replicates semi-conservatively

Hayflick Limit

Leonard Hayflick discovered that normal, differentiated somatic cells can only divide a set number of times before cell division ceases (or it could cause progeria)

Biological changes associated with aging

• Telomere shortening

• Stem cell exhaustion

• Imbalanced metabolism

• Inefficient cell communication

• Proteins become less functional

Mutation accumulation theory

Posits that aging results from the declining force of selection, leading to an accumulation of late- life mutations

DNA Proofreading

Errors due to DNA replication may result in cancer or lack of key functionality in cells. DNA Polymerase enzymes can detect and excise improperly paired bases before continuing elongation.

DNA Repair

Cells have mechanisms to identify and correct DNA errors. Chemical tags on parent strand differ from newly synthesized strand. Error is cut out and polymerase fills the gap

Telomeres

Repetitive noncoding DNA sequences at the ends of eukaryotic chromosomes that serve as protective caps

The End- Replication problem

Telomeres shorten as cells age

Telomerase

An enzyme to restore DNA to original length. (Embryonic stem cells, Immune system cells, Skin cells)

HeLa Cells

Oldest an most widely used immortal cell line in scientific research

DNA Extraction

Isolate DNA from other cellular components. DNA is often amplified by biotechnology techniques like PCR after extraction for use in other application.

Application of PCR

• For sequencing

• For use in DNA fingerprinting

• To achieve rapid prenatal diagnoses of genetic disorders

• To test for infections like HIV of extinct organisms

Humane Genome Project

• 1990-2003

• $1 Billion+ Project with goal of sequencing the haploid human genome (1 of each of 24 chromosomes)

Restriction Enzymes

Bacterial cells can recognize invading viral DNA as foreign and cut it up with restriction enzymes

Recombinant DNA Technology

Get a species to express genes from non-native DNA

Plasmids

Small, circular DNA molecules in bacteria separate from the rest of the genome

Gel Electrophoresis

DNA of differing lengths loaded into wells at cathode (-) end. Restriction enzymes are used to cut DNA into different sized pieces for DNA fingerprinting. Electric current is run, DNA that is shortest will travel fastest, furthest toward the anode (+) end

Using Electrophoresis to Perform DNA Sequencing

• Amplified DNA (PCR)

• Primers

• DNA polymerase

• Pool of normal nucleotides (ACGT)

Impacts of DNA sequencing Technology

• Finding the genetic causes of diseases

• Creating new targeted therapies (gene editing)

• Elucidation of evolutionary relationships