Transcription DNA  mRNA

Objectives Explain the purpose of transcription for a cell Explain the purpose of transcription for a cell Tell how RNA differs from DNA Tell how RNA differs from DNA Name the three main types of RNA Name the three main types of RNA Describe the process of transcription Describe the process of transcription

Review What was the purpose for DNA replication? What was the purpose for DNA replication? So cell division (mitosis & meiosis) can occur and each new cell created has a full set of DNA So cell division (mitosis & meiosis) can occur and each new cell created has a full set of DNA What are the Nitrogen bases of DNA? What are the Nitrogen bases of DNA? A, G, C, T A, G, C, T What is the sugar for DNA? What is the sugar for DNA? deoxyribose deoxyribose What does the structure of DNA allow? What does the structure of DNA allow? The strands are complementary of one another, meaning one strand is a template for the other. The strands are complementary of one another, meaning one strand is a template for the other.

Central Dogma Soon after there discovery of DNA structure, Watson and Crick, stated that information in molecular biology flows in one direction. From DNA to RNA to proteins. Soon after there discovery of DNA structure, Watson and Crick, stated that information in molecular biology flows in one direction. From DNA to RNA to proteins. The central dogma involves three process: The central dogma involves three process: Replication copies DNA Replication copies DNA Transcription converts a DNA message into a temporary ‘disposable’ copy of DNA called RNA Transcription converts a DNA message into a temporary ‘disposable’ copy of DNA called RNA Translation interprets an RNA strand into a string of Amino Acids which will turn into specific proteins. Translation interprets an RNA strand into a string of Amino Acids which will turn into specific proteins. Transcription video

What is RNA? What is RNA? 3 main differences between DNA & RNA? 3 main differences between DNA & RNA? RNA is like a “disposable copy” of a segment of DNA. RNA is like a “disposable copy” of a segment of DNA. RNA consists of long chains of nucleotides (like DNA) RNA consists of long chains of nucleotides (like DNA) Parts of a Nucleotide: 5 carbon sugar Phosphate group Nitrogenous base RNA sugar- Ribose RNA is single stranded RNA contains Uracil (U) in place of Thymine

Transcription makes 3 types of RNA Messenger RNA: mRNA Messenger RNA: mRNA Ribosomal RNA: rRNA Ribosomal RNA: rRNA Transfer RNA: tRNA Transfer RNA: tRNA

Function of mRNA Carries copies of gene instructions for assembling amino acids into proteins from nucleus to ribosome (transcription)

Function of rRNA Forms part of ribosomes, a cell’s protein factory Forms part of ribosomes, a cell’s protein factory Large subunit binds to tRNA Binding Sites Small subunit binds to mRNA

Function of tRNA Brings amino acids from the cytoplasm to a ribosome to help make the growing protein Brings amino acids from the cytoplasm to a ribosome to help make the growing protein anticodon Amino Acid

Transcription TRANSCRIPTION :The process of copying a sequence of DNA to produce a complementary (disposable) strand of RNA TRANSCRIPTION :The process of copying a sequence of DNA to produce a complementary (disposable) strand of RNA During this process, a GENE – not an entire chromosome – is transferred into an mRNA. During this process, a GENE – not an entire chromosome – is transferred into an mRNA. The cell needs this process because DNA has the information/code needed to make proteins AND DNA is too valuable to leave the nucleus, so it makes a disposable copy! The cell needs this process because DNA has the information/code needed to make proteins AND DNA is too valuable to leave the nucleus, so it makes a disposable copy! THIS IS A MAJOR PART IN PROTEIN SYNTHESIS!!!!! THIS IS A MAJOR PART IN PROTEIN SYNTHESIS!!!!!

Overview of Protein Synthesis: Ribosomes are made in nucleolus Ribosomes leave through the Nuclear pores on the nuclear membrane Some attach to ER, while others remain free floating Ribosomes begin attaching Amino Acids together to form proteins Proteins enter into RER to be modified and folded (shaped) into structures Vesicles form from RER and carry proteins to Golgi apparatus There proteins are packaged, sorted and/ or stored in Golgi Once the proteins are ready to leave, vesicles form to transport proteins throughout the cell and to other cells.

What are genes? What are genes? Genes are coded DNA instructions that control the production of proteins within a cell. Genes are coded DNA instructions that control the production of proteins within a cell. The code is held with the sequence of nitrogen bases in DNA. Like credit card numbers, unique to every person! REMEMBER: that a chromosome is made up of multiple genes, and transcription only copies specific genes, 1 at a time. REMEMBER: that a chromosome is made up of multiple genes, and transcription only copies specific genes, 1 at a time.

Step 1: RNA polymerase binds to promoters on DNA strand and begins to unwind a segment of DNA that corresponds to the gene it is copying. RNA polymerase binds to promoters on DNA strand and begins to unwind a segment of DNA that corresponds to the gene it is copying. start site nucleotides transcription complex

Step 2: RNA polymerase, using only one strand of DNA as a template, adds on free-floating RNA nucleotide RNA polymerase, using only one strand of DNA as a template, adds on free-floating RNA nucleotide As RNA polymerase moves along the DNA, a growing RNA strands hangs freely as it is transcribed, and the DNA helix zips back together. As RNA polymerase moves along the DNA, a growing RNA strands hangs freely as it is transcribed, and the DNA helix zips back together. *A - U, C – G there are NO T’s DNA RNA polymerase moves along the DNA

Step 3: Once the entire gene has been transcribed, the RNA strand detaches completely from the DNA. Once the entire gene has been transcribed, the RNA strand detaches completely from the DNA. Exactly how RNA polymerase recognizes the end of a gene is very complicated but we will discuss as it reaching a Stop signal. Exactly how RNA polymerase recognizes the end of a gene is very complicated but we will discuss as it reaching a Stop signal.

RNA polymerase RNA polymerase is an enzyme that plays multiple roles in transcription process RNA polymerase is an enzyme that plays multiple roles in transcription process Unzips the DNA molecule where gene is found Unzips the DNA molecule where gene is found Adds free floating nucleotides to make mRNA strand Adds free floating nucleotides to make mRNA strand What it DOESN’T do is proof read it’s work like DNA polymerase.

How does RNA polymerase know How does RNA polymerase know where to start and stop? Promoter sites- which have specific nitrogen base sequences (TAC) Promoter sites- which have specific nitrogen base sequences (TAC) Promoters are signals in DNA to indicate where an enzyme can bind to make RNA Promoters are signals in DNA to indicate where an enzyme can bind to make RNA Stop signals/sites – specific sequence of nitrogen bases that tell the RNA polymerase to stop and fall off. Stop signals/sites – specific sequence of nitrogen bases that tell the RNA polymerase to stop and fall off.

replication transcription translation growing RNA strands DNA one gene