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 single- stranded 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 nucleotides transcription complex 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 growing RNA strands DNA one gene 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. 16