Protein SynthesisTranscription and Translation 8.4 and 8.5
Bell Work • 1. A structure in the nucleus of the cell consisting of one long strand of DNA that is tightly coiled • 2. Provides blueprint for synthesis of proteins • 3. A specific location on a chromosome, consisting of segments of DNA, that codes for a specific protein • 4. List two nucleic acids. • 5. List the three parts of a nucleotide. • 6. Which sugar does RNA contain? • 7. Which sugar does DNA contain? • 8. List the four bases that RNA has. • 9. List the four bases that DNA has. • 10. Which molecule has the shape of a double helix? • 11. What happens during DNA replication? • 12. When does DNA replication occur?
Focus Questions • What is protein synthesis? • Define transcription and explain the process. • What is the function of mRNA?
What is protein synthesis? • Protein synthesis - • Making proteins
RNA carries DNA’s instructions. • The central dogma states that information flows in one direction from DNA to RNA to proteins.
replication transcription translation • The central dogma includes three processes. • Replication • Transcription • Translation • RNA is a link between DNA and proteins.
What is transcription? • The process by which the DNA is copied to make a strand of RNA • Through this process the DNA code is transferred out of the nucleus to the ribosome
transcription complex start site nucleotides Transcription- How does it happen? • An enzyme attaches to the exact location on the DNA molecule where the gene is found, causing the two strands of DNA to separate at that location.
DNA Transcription • Complementary RNA nucleotide bases bond to the bases on one of the separated DNA strands. DNA RNA A bonds with U T bonds with A C bonds with G G bonds with C
DNA Transcription • Nucleotides of RNA bond together, forming a single-stranded molecule of RNA that peels away from the DNA strand and the two DNA strands rejoin. This is called messenger RNA (mRNA).
Transcription • The messenger RNA leaves the nucleus
Try This: Transcribe the message • Use the DNA code to make a complementary strand of mRNA. • TAC GGG ATT TCC GAG CCA ATC CAG CCA ACT • Questions • 1. What is made during transcription? • 2. Where does the mRNA go after transcription?
More Practice with transcription • Go to class web page. • Click on link for Build a Protein. • Make the mRNA. • Get signature of teacher in lab notebook. • Stop for now.
8.5 Focus Questions • 1. Define translation. • 2. How is messenger RNA involved in translation? What is a codon? Distinguish start and stop codons. How are the codons related to the amino acids? • 3. How is transfer RNA involved in translation? What is an anticodon? Draw a diagram and label the parts of tRNA. • 4. Summarize the steps of translation.
Amino acids are coded by mRNA base sequences. • Translation is the process of interpreting the genetic message and building proteins.
codon for methionine (Met) codon for leucine (Leu) Describe the messenger RNA (mRNA) • Carries the genetic message to the ribosome • A codon is a sequence of three nucleotides • Each codon specifies a specific amino acid that will be placed in a chain to build a protein. • The sequence of mRNA nucleotides determines the order of amino acids and which protein is produced
The genetic code matches each RNA codon with its amino acid or function. • The genetic code matches each codon to its amino acid or function. • three stop codons • one start codon, codes for methionine
Describe the transfer RNA (tRNA) • Transfer RNA (tRNA) • tRNA transfers the amino acid into the correct sequence • There are 20 different types of tRNA (one for each amino acid) • At one end is the anticodon site that is complementary to mRNA codon • At the other end is the specific amino acid
How are Ribosomes involved? • Translation begins when the mRNA attaches to the ribosome. • The ribosomes contain proteins and ribosomal RNA (rRNA)
Ribosomes consist of two subunits. • The large subunit has three binding sites for tRNA. • The small subunit binds to mRNA.
The tRNAbinds to a start codon and signals the ribosome to assemble. • A complementary tRNA molecule binds to the next exposed codon, bringing its amino acid close to the first amino acid.
The ribosome helps form a polypeptide bond between the amino acids and the chain begins to form
The now empty tRNA molecule exits the ribosome to pick up another amino acid. • A complementary tRNA molecule binds to the next exposed codon. • The process ends once the stop codon is reached.