DNA, RNA, and Protein Synthesis

Function of DNA as “master” program• DNA codes for the primary structure of a protein which impacts the

tertiary structure, which determines the function of the protein• DNA doesn’t control protein synthesis directly…instead

DNA VS RNA

Differences Between DNA and RNA

DNA RNAdouble-stranded single-stranded

sugar = deoxyribose sugar = ribose

bases = A,T,C,G bases = A,U,C,G(uracil takes the place of thymine)

Types of RNAMessenger RNA (mRNA) – temporary copy of a gene

that carries information from nucleus to ribosomeRibosomal RNA (rRNA) – a type of RNA that makes up

ribosomes (where protein synthesis takes place)Transfer RNA (tRNA) – a type of RNA that attaches to

the amino acids used to make the protein

mRNA tRNA rRNA

How is DNA like the English language?• Language analogy – 26 letters in the

English language that can combine to make millions words• Genetic code – DNA is made of 4 letters

(Nitrogen bases), and 3 letters form a word (amino acid); but there are only 20 possible “words”

*So how many DNA nucleotides are needed to code for the 20 possible amino acids?

Why are Proteins important?• Material that makes up cell structures or tissues

(keratin, collagen, myosin, etc.)• Enzymes that make the chemical reactions of living

systems happen quickly• Proteins bond to other molecules (ex. hemoglobin &

oxygen in blood)• Key role in communication; hormones – chemical

signals given off by cells that regulate behavior of cells in different area

1. Transcription – the process of making mRNA from DNA

- occurs in nucleus2. Translation – the process in which amino acids (coded for in the mRNA) are added to a protein being made = PROTEIN SYNTHESIS

- occurs in cytoplasm

Protein Synthesis requires 2 processes:

RNA Synthesis (Transcription)• Produces mRNA• One strand of DNA acts as the

template for RNA synthesis (C ↔ G; A → U; T → A)• Main enzyme = RNA polymerase,

which adds the RNA nucleotides to pair with the DNA

• Occurs in 3 stages

Transcribe the following DNA:

Transcription – 3 Stages1. Initiation

- RNA polymerase binds to the DNA at the promoter region. It is directed to this region by proteins called initiation factors.

2. Elongation- RNA polymerase moves along the coding strand of DNA away from the promoter, building the RNA strand.

3. Termination- RNA polymerase reaches the terminator region of the DNA & is released from the DNA with the primary transcript.

RNA Processing• All 3 types of RNA (mRNA, tRNA, &

rRNA) are processed in the nucleus before they leave it.• This can involve adding, chemically

changing, and/or removing nucleotides. (proofreading)

RNA SplicingAll RNA transcripts undergo processing called splicing.

• The removal of meaningless segments of RNA, called introns, and fusing together the remaining, meaningful sections, called exons.• Requires precise recognition of the site to be cut by a restriction enzyme

Protein Synthesis Step 2- Translation• mRNA is translated into the amino acid

sequence of a protein.• It happens on ribosomes in the cytoplasm.• ATP provides the energy to form the bonds.• Divided into same 3 stages as Transcription:

initiation, elongation, & termination.

• tRNA acts as a carrier molecule that transfers amino acids to the ribosome.• A tRNA anticodon matches with an mRNA codon. (3 nitrogen bases)

Practice:

mRNA: AUG CGA AAC UCA

tRNA:

tRNA and Amino Acids-There are 64 possible

codon combinations (3 nitrogen bases) BUT only 20 amino acids.

- SO – some codon “words” code for the same amino acid.

- We can interpret or “read” this code using a codon table:

Let’s try “AUG”

Now try:• CCU• CCG• UGA• GGA

What do you notice?