Topic 25 – RNA and protein synthesis Day 2 of 3 Topic 25 – RNA and protein synthesis

DNA Replication Bell Ringer The sequence below represents the bases of a single strand of a DNA molecule. Complete the complementary strand of DNA.   A T T A C G A T C T G C A C A A G A T C C T

THINK – PAIR – SHARE Where in the cell is DNA stored? Where are proteins build in the cell? What are some functions of proteins? If DNA cannot exit the nucleus, how can cells make proteins? To the Teacher: I like to use the analogy of a school principal, who cannot leave his office, but has important instructions to distribute to the teachers in the classrooms. How can he send orders to teachers working in the classroom? A messenger. This messenger will bring the instructions to the rest of the school. For a gene to work a part of the nucleotide sequence of DNA must be copied into RNA.

What are we learning today? Benchmark Objectives SC.912.L.16.5 – Explain the basic processes of transcription and translation, and how they result in the expression of genes. Compare and contrast RNA and DNA. Describe the process of transcription. To the Teacher: Introduce today’s benchmark. Read or have a student read the day’s objectives.

What is the essential question? Suppose you start with two DNA strands: ACCGTCAC and TCGCACGT. Use the “rules” of base paring to list the bases on mRNA strands transcribed from those DNA strands.

What is the essential vocabulary? RNA polymerase – enzyme that binds to DNA and separates the DNA strands during transcription. Transcription – Process during which RNA molecules are produced by copying part of the nucleotide sequence of DNA. Intron – sequence of DNA that is not involved in coding for a protein. Exon – sequence of DNA that is involved in coding for a protein.

How is DNA like or not like RNA? RNA and DNA are nucleic acids. RNA, like DNA consist of a long chain of nucleotides. There are three main differences between RNA and DNA: The sugar in RNA is ribose, the sugar in DNA is deoxyribose. RNA is single stranded, DNA is double stranded. RNA contains uracil (U) DNA contains thymine (T).

What are the three types of RNA? Abbrev. Name Function Structure mRNA Messenger RNA Carries copies of instructions for assembling proteins from DNA to ribosomes. Single-stranded tRNA Transfer RNA Reads mRNA sequence and transfers each amino acid to the ribosome. A clover leaf rRNA Ribosomal RNA Binds corresponding amino acid to a growing peptide chain Complex, with proteins

How does transcription work? Right-click slide Select “Play” 9

How does transcription works? RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA during a process called transcription. Transcription requires an enzyme known as RNA polymerase. RNA polymerase only binds to regions in DNA known as promoters with specific base sequences. Promoters are signals in DNA that indicate to the enzyme where to bind to make RNA.

How does transcription works? RNA polymerase binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA. When RNA polymerase reaches a termination signal in the DNA, the DNA and new RNA are released.

How does transcription work? A certain gene has the following sequence of nucleotides. From left to right, write the sequence of the mRNA molecule transcribed from this gene. DNA 3’ GACAAGTCCACAATC 5’ mRNA

How does transcription works? DNA template strand DNA 3 5 A C C A A A C C G A G T molecule T G G T T T G G C T C A Gene 1 5 3 TRANSCRIPTION Gene 2 U G G U U U G G C U C A mRNA To the Teacher: Click on image to access video. http://www.hhmi.org/biointeractive/media/DNAi_transcription_vo2-lg.wmv 5 3 Codon TRANSLATION Protein Trp Phe Gly Ser Gene 3 Amino acid

Click the Picture Below for Transcription in action

What is RNA editing? The DNA of eukaryotic genes contain sequences of nucleotides, called introns, that are not involved in coding proteins. The DNA sequences of nucleotides that code for proteins are called exons. When the RNA molecules are formed, both the introns and exons are copied from the DNA. However, introns are cut out of RNA molecules while they are still in the nucleus. The remaining exons are then spliced back together to form the final mRNA.

What is the essential question? Suppose you start with two DNA strands: ACCGTCAC and TCGCACGT. Use the “rules” of base paring to list the bases on messenger RNA strands transcribed from those DNA strands.

mRNA Model Adenine – orange Guanine – dark blue Cytosine – red Uracil – purple Ribose – light blue Phosphate - pink RNA: Ribose Phosphate A, G, U, C