Gene ExpressionGene: contains the recipe for a protein

1. is a specific region of DNA on a chromosome2. codes for a specific mRNA

mRNA: exits the nucleus and associates with ribosomes

1. carries the code for a specific protein to the cytoplasm2. primary structure of a protein is encoded by the mRNA base sequences

3. sequence of mRNA bases is encoded by DNA (genes)

Two processes involved:1. transcription - mRNA synthesis (copy the code)2. translation - protein synthesis (translate the code)

DNA StructureA. Rosalind Franklin

X-ray crystallographyDNA exists as a helix

B. Watson and Crick1. DNA is a double helix2. two complementary strands

Nucleic AcidsA. Building blocks are nucleotides

1. 5-carbon sugar (ribose or deoxyribose)2. phosphate group3. nitrogenous/organic base (varies)

B. DNA is a polymer made using 4 different nucleotides- the four nucleotides differ only in their bases

D. Nucleotides are bonded via their phosphate groups 1. phosphate binds to a sugar of another nucleotide2. sugars and phosphates form a “backbone” 3. bases project from backbone (forming side chains)

4. H bonds form between bases of opposing side chainsa. DNA is double strandedb. forms a double helix

Double helix:

E. Law of complementary base-pairing (Chargaff’s rules)1. adenine to thymine2. guanine to cytosine

The sequence of bases in one chain (strand) determines the sequence of bases in the other chain.

F. RNA structure (3 major differences with DNA)1. sugar is ribose2. uracil instead of thymine 3. single-stranded

G. Classes of RNA1. mRNA: carries coded info to the ribosomes

G. Classes of RNA1. mRNA: carries coded info to the ribosomes2. rRNA: structural molecule of ribosomes

G. Classes of RNA1. mRNA: carries coded info to the ribosomes2. rRNA: structural molecule of ribosomes 3. tRNA: brings amino acids to ribosomes for protein synthesis

All three types of RNA necessary for protein synthesis.

DNA ReplicationA. Copying of DNA

done before mitosis (S phase)

DNA ReplicationB. Process

1. unzip the double helix2. each strand used as a template3. complementary strands constructed4. new DNA molecules identical to the original5. enzyme (DNA polymerase) also “proofreads”

DNA ReplicationB. Process

1. unzip the double helix2. each strand used as a template3. complementary strands constructed4. new DNA molecule identical to the original5. enzyme (DNA polymerase) also “proofreads”

TranscriptionOnly a few genes usually active at any one time in a cell.

If a gene is active, then coded info in gene must be copied onto an mRNA molecule.

Transcription = DNA-directed RNA synthesis.

A. Transcription occurs in the nucleusB. RNA polymerase

1. unzips DNA double helix2. only at area to be transcribed

3. H bonds between strands are broken4. mRNA is built using one DNA strand as template

C. Formed mRNA detaches from template DNA (gene)D. Can make many copies quickly if needed

E. Post-transcriptional modifications1. removal of introns2. exons spliced together