BIOL 107 - Topic 5: DNA Structure, Function, and the Central Dogma

Heredity

Transmission of traits from one generation to the next

Frederick Griffith experiment

Studied mice infected with different strains of Streptococcus pneumonia bacteria

• injection of S and/or R cells

Transformation

Change due to uptake of external DNA by a cell

• transfer of trait information between cells

Avery, MacLeod, McCarty experiment

Took samples of heat-killed S cells and removed specific components using enzymes

Erwin Chargaff experiment

Examined the chemical composition of DNA in a variety of species

• measured the amount of each base (A, C, G, T)

• all DNA is made of the same 4 bases

• purines = pyrimidines

Virus

A non-living, infectious, biological particle

• genetic material (DNA or RNA) surrounded by a capsid (protein coat)

Bacteriophage

A virus that infects bacteria

• takes over the bacterial cell and turns it into a virus production factory

• composed of a protein coat and DNA

Radioactive Isotope

An unstable form of an element that emits detectable energy

Hershey and Chase experiment

Used radioactive protein and DNA components in bacteriophage to infect bacterial cells

• viral DNA enters bacterial cells and provides instructions to reprogram bacteria

Wilkins and Franklin

First studied the structure of DNA

Watson and Crick

Built a structural model to interpret Franklin’s results of DNA structure

• fixed width of 2nm

• antiparallel

• complementary base-pairing

DNA Replication

DNA-dependent synthesis of new DNA

• cell division

• two identical copies

Primase

Synthesizes RNA primer required for DNA polymerase to be able to add nucleotides

DNA Polymerase

Synthesizes the DNA strand from primer

• incorporates new nucleotides onto the 3’ end

• forms phosphodiester bonds

• energy comes from hydrolysis of the triphosphate of the incoming nucleotide

The Central Dogma

The theory that information is transferred in a one-way path from DNA to protein

DNA → RNA → Protein

Gene

A unit of hereditary information consisting of a specific sequence of nucleotides in DNA

• each gene has a unique sequence

Gene Expression

The process by which DNA directs the synthesis of proteins

Transcription

Synthesis of RNA by copying of a DNA template

Translation

Synthesis of a polypeptide using the information encoded in mRNA

• produces a specific sequence of amino acids

Initiation (Transcription)

The first stage in transcription where molecules assemble at the promoter and synthesis of an RNA copy of the gene begins

Elongation (Transcription)

The second step in transcription where RNA polymerase moves along the gene extending the RNA chain

• incorporates new RNA nucleotides onto the 3’ end of a growing RNA molecule

• forms phosphodiester bonds

Termination (Transcription)

The third step in transcription where transcription ends and the RNA transcript and RNA polymerase are released

• use of terminators that are specific DNA sequences that end the transcription of the gene

Promoter (Initiation)

The specific sequence of DNA where RNAP binds and begins transcription

• tells RNAP where to start

• binds directly to the DNA strand

pre-mRNA

The initial RNA transcript before modifications have been made

Mature mRNA

An RNA transcript that has been modified

• ready to leave the nucleus to do its job

Introns

Non-coding or intervening sequences

• don’t code for anything important

• are “cut out” by spliceosome enyzmes

Exons

Coding or expressed sequences that encodes for polypeptide chains

• spliced together by spliceosome enzymes

Spliceosome Enzyme

An enzyme complex that cuts out intros from pre-mRNA and joins exons together

• produces mRNA with continuous protein coding sequence

Ribosome

Enzyme complexes in the cell that contains rRNA and uses information in mRNA to attach amino acids in the correct order

• catalyzes the formation of peptide bonds between amino acids (order determined by mRNA)

Free Ribosomes

Ribosomes that are loose in the cytoplasm and make proteins that function in the cytosol

Bound Ribosomes

Ribosomes attached to the outside of the ER and nuclear envelope

Chaperones

Proteins that facilitate the folding of other proteins

• speeds up the rate at which proteins fold (like enzymes)

• present in the cytosol, ER, golgi apparatus

Endoplasmic Reticulum (ER)

A network of membrane tubules and sacs called cisternae

• the inside space is called the lumen

Rough ER

The site of protein synthesis

• proteins are inserted into the membrane or pass through pores into ER lumen

• covered with bound ribosomes

• contains enzymes for protein modification

Golgi Apparatus

Flattened sacs of membrane (cisternae) in stacks that functions to modify proteins and targets proteins to their final destination

• “sorting terminal” of the cell

• cis: receives vesicles from ER

• trans: vesicles bud off and sent to other sites

The Endomembrane System

The network of organelles that work together to synthesize, transport, and export proteins and lipids

• organelles are physically attached through continuous membrane or through transfer of membrane via vesicles