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Chapter 8 Section 8.4: DNA Transcription 1 Objectives • SWBAT describe the relationship between RNA and DNA. • SWBAT identify the three kinds of RNA and their functions. • SWBAT compare transcription to replication. 2 Vocabulary • Central dogma • RNA – Messenger RNA (mRNA) – Ribosomal RNA (rRNA) – Transfer RNA (tRNA) • Transcription • RNA polymerase 3 RNA Carries DNA’s Instructions • Central Dogma of molecular biology states that information flows in one direction: from DNA to RNA to Proteins. 4 RNA Carries DNA’s Instructions • Replication copies DNA • Transcription converts a DNA instruction into an intermediate molecule called RNA (ribonucleic acid). • Translation interprets the RNA message and turns it into a protein. 5 RNA Carries DNA’s Instructions • In prokaryotic cells, DNA replication, transcription and translation all take place in the cytoplasm due to no nucleus. • In eukaryotic cells, DNA replication and transcription take place in the nucleus while translation occurs in the cytoplasm. • In eukaryotic cells, RNA is a link between DNA in the nucleus and protein synthesis in the cytoplasm. 6 RNA (ribonucleic acid) • Like DNA, RNA is a chain of nucleotides. – Also made up of a phosphate group, ribose (a sugar), and a nitrogen containing base. – “RNA can be thought of as a temporary copy of DNA that is used and then destroyed. 7 RNA (ribonucleic acid) RNA differs from DNA in three different ways: 1. RNA has a different sugar, ribose. 2. The nucleotide uracil replaces thymine in RNA. 3. RNA is a singlestranded molecule whereas DNA is double-stranded. 8 Transcription Practice • Transcribe the following “genes.” – AACGTTCCG – UUGCAAGGC – ACGTTAACG – UGCAAUUGC – GCCGAATCG – CGGCUUAGC 9 Transcription • Transcription is the process in which a sequence of DNA is utilized to produce a complementary strand of RNA. • During transcription, a gene or genes are transcribed into strands of RNA (whole chromosomes are not transcribed into RNA, only genes). – The genes, held in DNA, are instructions and the RNA (messenger RNA) acts as the courier. 10 Transcription • In the process of transcription, DNA polymerases are replaced with RNA polymerases. – Remember, they are enzymes that catalyze transcription and replication reactions. – RNA polymerases bInd nucleotides together to make RNA chains. 11 Transcription Transcription is catalyzed by RNA polymerase. • RNA polymerase and other proteins form a transcription complex. • The transcription complex recognizes the start of a gene and unwinds a segment of it. start site transcription complex nucleotides 12 Transcription • Nucleotides pair with one strand of the DNA. • RNA polymerase bonds the nucleotides together • The DNA helix winds again as the gene is transcribed. 13 Transcription The RNA strand detaches from the DNA strand once the gene is transcribed. RNA 14 Types of RNA • Transcription makes several types of RNA, the three that concern us are: – Messenger RNA (mRNA) carries the message that will be translated to form a protein (made by transcription of DNA). – Ribosomal RNA (rRNA) forms part of ribosomes where proteins are made. – Transfer RNA (tRNA) brings amino acids from the cytoplasm to a ribosome. 15 Transcription and Replication • Transcription and replication both involve complex enzymes and complementary base pairing. • The two processes have different end results. – Replication copies all the DNA; transcription copies a gene. – Replication makes one copy; transcription can make many copies. one gene growing RNA strands DNA 16