Transcription and Translation

1. Transcription and Translation Ch 10

2. DNA Nucleotides • A DNA nucleotide is made of a 5-carbon deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T).

3. DNA Strands Run Antiparallel Hydroxyl is the terminating molecule of the 3’ end Phosphate is the terminating molecule of the 5’ end

4. Flow of Genetic Information • The flow of genetic information can be symbolized as DNA → RNA→ protein. DNA and RNA

5. RNA Structure and Function • RNA has the sugar riboseinstead of deoxyribose and uracil in place of thymine. • RNA is single stranded and is shorter than DNA. • Types of RNA • Cells have three major types of RNA: • messenger RNA(mRNA) • ribosomal RNA (rRNA) • transfer RNA (tRNA)

6. 3 Types of RNA • messenger RNA (mRNA): Transcribes message from DNA strand and delivers the message to the ribosomes. • transfer RNA (tRNA). Transfers amino acids to mRNA based on sequence of codons. • ribosomal RNA (rRNA). The ribosomes, which are the site of mRNA attachment and protein synthesis.

7. Transcription • Duringtranscription, DNA acts as a template for directing the synthesis of RNA.

8. Transcription and Genetic Code • The nearly universal genetic codeidentifies the specific amino acids coded for by each three-nucleotide mRNA codon.

9. Translation • Steps of Translation • During translation, amino acids are assembled from information encoded in mRNA. • As the mRNA codons move through the ribosome, tRNAs add specific amino acids to the growing polypeptide chain. • The process continues until a stop codon is reached and the newly made protein is released.

10. TRANSCRIPTION DNA (a) Prokaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing. (b) Eukaryotic cell. The nucleus provides a separatecompartment for transcription. The original RNAtranscript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA. Transcription: prokaryotes vs eukaryotes

11. TRANSCRIPTION DNA mRNA Ribosome TRANSLATION (a) Prokaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing. Polypeptide (b) Eukaryotic cell. The nucleus provides a separatecompartment for transcription. The original RNAtranscript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA.

12. TRANSCRIPTION DNA mRNA Ribosome TRANSLATION (a) Prokaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing. Polypeptide Nuclear envelope DNA TRANSCRIPTION (b) Eukaryotic cell. The nucleus provides a separatecompartment for transcription. The original RNAtranscript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA.

13. TRANSCRIPTION DNA mRNA Ribosome TRANSLATION (a) Prokaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing. Polypeptide Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA (b) Eukaryotic cell. The nucleus provides a separatecompartment for transcription. The original RNAtranscript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA.

14. TRANSCRIPTION DNA mRNA Ribosome TRANSLATION (a) Prokaryotic cell. In a cell lacking a nucleus, mRNAproduced by transcription is immediately translatedwithout additional processing. Polypeptide Nuclear envelope DNA TRANSCRIPTION Pre-mRNA RNA PROCESSING mRNA Ribosome TRANSLATION (b) Eukaryotic cell. The nucleus provides a separatecompartment for transcription. The original RNAtranscript, called pre-mRNA, is processed in various ways before leaving the nucleus as mRNA. Polypeptide

15. Non-template strand of DNA Elongation RNA nucleotides RNA polymerase T A C C A T A T 3 C U 3 end T G A G G C 5 A A T A G G T T Direction of transcription (“downstream) 5 Template strand of DNA Newly made RNA

16. DNA strand prior to transcription

17. free floating nucleotides in the nucleus of a cell

18. Step 1; RNA polymerase binds to promoter (initiator) site on DNA . DNA unwinds and separate at hydrogen bonds. DNA bases used as a template for making new strand of mRNA. • Only one side of the DNA molecule is used*

19. Step 2: RNA polymerase continues building mRNA strand from DNA template strand in one direction (5-3). Once a stop codon (terminator) is reached, the mRNA breaks off of the DNA strand. DNA recoils -.

20. Step 3: The completed RNA strand moves out of the nucleus through a nuclear pore.

21. Step 1: (Initiation) mRNA binds to small ribosomal subunit in the cytoplasm.

22. Step 2: tRNA anticodon (carrying met) attaches to complementary mRNA codon and ribosome.

23. Step 3: (elongation) tRNA anticodons continue to attach to complementary mRNA codons and ribosome, bringing amino acid close enough to form peptide bonds.

24. Step 4: Amino acid chain (protein) continues to grow until stop sequence is reached (termination)

25. RNA polymerase DNA mRNA Polyribosome Direction of transcription 0.25 m RNA polymerase DNA Polyribosome Polypeptide (amino end) Ribosome mRNA (5 end) Multiple polypeptides will be translated simultaneously

26. Human Genome • The entire gene sequence of the human genome, the complete genetic content, is now known. • To learn where and when human cells use each of the proteins coded for in the approximately 30,000 genes in the human genome will take much more analysis.