DNA, RNA, Transcription, and Translation (Protein Synthesis)

DNA, RNA, Transcription, and

Translation (Protein Synthesis)

Standard H.B.4 The student will demonstrate an understanding of the specific mechanisms by which characteristics or traits are transferred from one generation to the next via genes.

Conceptual Understanding

H.B.4B In order for information stored in DNA to direct cellular processes, a gene needs to be transcribed from DNA to RNA and then must be translated by the cellular machinery into a protein or an RNA molecule. The

protein and RNA products from these processes determine cellular activities and the unique characteristics of an individual. Modern techniques in biotechnology can manipulate DNA to solve human problems.

Performance Indicator

H.B.4B.1 Develop and use models to describe how the structure of DNA determines the structure of resulting proteins or RNA molecules that carry out the essential functions of life.

Central Dogma

• Information flows in one direction

• DNA to RNA to protein

• Transcription is the process of

converting DNA to RNA

• Translation is the process of

interpreting RNA into a string of amino

acids (protein)

RNA Review

• similar to DNA except

• RNA is single-stranded

• contains the base Uracil instead of Thymine

• contains the sugar ribose instead of deoxyribose

• RNA is a temporary copy of DNA that is used and then destroyed

Protein Synthesis in a Nut Shell

• When a particular protein is needed, the cell must make the

protein through the process of transcription and translation

(protein synthesis).

• DNA molecules (which contain the code) do not leave the nucleus of the

cell.

• Protein synthesis occurs on ribosomes located outside of the nucleus.

• Therefore, the code must be carried from the nucleus to the cytoplasm.

Protein Synthesis: Process 1: Transcription

• Transcription is the process by which a portion of the molecule of DNA is copied into a complementary strand of RNA.

• Don’t forget the base pairing rules!

• DNA RNA

• A U

• G C

• C G

• T A

Protein Synthesis: Process 1: Transcription

• The process of transcription takes

place as follows:

• 1. An enzyme (helicase) attaches to

the DNA molecule at the gene of

interest.

Protein Synthesis: Process 1: Transcription

• 2. The two strands of DNA separate

at that location.

Protein Synthesis: Process 1: Transcription

• 3. Complementary RNA nucleotides bond to the nitrogenous bases on one

of the separated DNA strands.

• The enzyme, RNA polymerase, assists

Protein Synthesis: Process 1: Transcription

• 4. The chain of RNA nucleotides forms a single-stranded molecule of RNA

by using the DNA strand as a template.

Protein Synthesis: Process 1: Transcription

• 5. When a stop codon is reached,

the RNA strand separates from

the DNA molecule, leaves the

nucleus and goes through the

nuclear membrane into the

cytoplasm.

Protein Synthesis: Process 1: Transcription

• 6. The two DNA strands rejoin.

• mRNA strand leaves the nucleus and goes

through the nuclear membrane into the

cytoplasm.

Types of RNA

• 3 types of RNA are made during transcription

1. Messenger RNA (mRNA) – will be translated into a protein

2. Ribosomal RNA (rRNA) – forms part of a ribosome

3. Transfer RNA (tRNA) – brings amino acids from the cytoplasm to

the ribosome to help make a protein

Checking for Understanding: Transcribe DNA

to RNA

ATA GAC TTG CTT AAA GGC CTA AAT CCA

UAU CUG AAC GAA UUU CCG GAU UUA GGU

Animation: Transcription

Translation & Triplet Code

• Translation is the process by which the genetic message, carried by the mRNA, is used to assemble a protein.

• Every 3 nucleotide sequences is called a codon

• Codons will code for a specific amino acid

• For example, if the DNA sequence was GAC, then the RNA sequence becomes CUG (transcription) and the amino acid that is coded is Leucine

Start and Stop Codons

• start codon – signals the start of

translation with the amino acid

methionine (AUG)

• stop codon – signals the ending of

translation

• 3 stop codons (UAA, UAG and UGA)

Protein Synthesis: Process 2: Translation

• The process of translation takes place as follows:

• 1. The mRNA attaches to a ribosome, which contains proteins

and ribosomal RNA (rRNA).

• The function of ribosomes is to assemble proteins according to the

genetic message

Protein Synthesis: Process 2: Translation

• 2. transfer RNA (tRNA), brings

amino acids to the ribosome in the

order specified by the codon

sequence on the mRNA

Protein Synthesis: Process 2: Translation

• 3. When another tRNA

drops off its amino acid, the

first tRNA will disconnect

and can go pick up another

amino acid

Protein Synthesis: Process 2: Translation

• 4. Ribosome forms a peptide

bond between the amino acids

• Sequence is repeated until the

ribosome reaches a stop codon

• This creates a polypeptide or

protein

How does tRNA pick up the amino acid?

• tRNA has an anticodon, a region that consists of three nucleotide bases that are complementary to the codon of mRNA, at one end.

• tRNA goes to the cytoplasm and picks up the amino acid that the mRNA codes for.

• The other end of the tRNA molecule binds to the specific amino acid that is determined by the mRNA codon

Animation: How Translation Works

Check for Understanding

• Transcribe DNA to RNA

• DNA STRAND: ATA GAC TTG CTT AAA GGC CTA AAT CCA

• RNA STRAND:

• Translate RNA to the AntiCodons

• AntiCodons:

• Amino Acids: