Understanding Gene Structure and Transcription Processes
School
University of British Columbia**We aren't endorsed by this school
Course
BIO 112
Subject
Biology
Date
Dec 10, 2024
Pages
8
Uploaded by EarlUniverseKangaroo38
Week 5 - Transcription & Gene Structure:Learning Objectives ● Identify the 3 main components of a gene. (Promoter, coding sequence, terminator)● Explain and Identify upstream and downstream regions of the genome when describing the● relative location of gene structures.● Explain the difference between the template strand and the non-template (coding) strand in DNA.● Predict the RNA sequence transcribed from the DNA sequence of a transcription unit.- Transcription is when DNA is converted into mRNADNA replication is semiconservative- every double helix in the new generation of an organism consists of one complete “old” strand and one complete “new” strand wrapped around each otherEach new strand of DNA contains a new strand and an old strand
The DNA strand are antiparallel- run in opposite directions5’ → 3’ and 3’ to 5’ → 3’5’ AGTACTGA 3’ (template strand)3’ TGATGACT 5’ DNA complementary base pairingA with T and G with CHydrogen-bonds hold nucleotides together- A with G are Purines (2 carbon-nitrogen rings)- C and T are pyrimidines (single carbon-nitrogen ring)- G and C are held together by 3 hydrogen bonds- A and T are held together by 2 hydrogen bondsDNA replication process:Genetic flow of information in prokaryotes and eukaryotesProkaryotes:- transcription/translation occur in the cytoplasmEukaryotes:- Transcription occurs in the nucleus while translation occurs in the cytoplasmDNA synthesis moves from 3’to 5’ - Always look for 3’ to 5’ strand (coding strand)- Make sure promotor moves towards terminator for 3’ to 5’
Self assessment Q’s:- How does the sequence of a molecule made of DNA, made up of many subunits of nucleotides of only 4 nucleotides, encode the enormous amount of genetic information present in living organisms?Answer: The nucleotides can occur in any order. Any base on a strand of DNA can be followed by another base (A,T, G, C) which gives rise to any potential order in a gene- How are parental strands in a DNA molecule used in DNA replication?Answer: During DNA replication, the two strands of the DNA strand unwind by the enzyme helicase, disrupting the hydrogen bonds and base stacking that help hold the strands together. Each parental strand serves as a template for a new complementary strand of DNA because of the specific pairing of the bases: A on the template 5’ → 3’ will always specify a T on the new strand and vice versa. G on the template 5’ → 3’ will always specify a C on the new strand and vice versa. The end result is of DNA replication is 2 daughter molecules that have identical sequences to their parental strand
TRANSCRIPTION:Ribosomes: a complex structure of RNA and protein that synthesizes proteins- In eukaryotes, DNA is located in the nucleus - In prokaryotes, DNA is located in the cytoplasm- The 5-carbon sugar in RNA is ribose- The additional hydroxyl on ribose explains why it more unstable because the hydroxyl functional group is highly reactive- U has an H attached to its number 5 carbon while T has a methyl group (CH3)- 5’ end of RNA molecule is a triphosphate and 5’ end of a DNA molecule is a monophosphate- RNA molecules are much shorter to DNA - RNA molecule used in protein synthesis consists of a few thousand nucleotides while a DNA molecule consists of millions or tens of millions nucleotides- Some RNA molecules can act as enzymes to facilitate chemical reactions- Many scientists think that RNA was the OG info storing molecule because it has DNA features and protein feature (RNA world hypothesis)- In transcription, DNA is used as a template to make complementary DNADNA is used as a template to make complementary DNA in transcription- As a region of DNA unwinds, one strand is used as a template for the making of an RNA sequence - Produced by polymerization of ribonucleoside triphosphates
- Done by enzyme RNA polymerase (adds nucleotides to the 3’ end)Comparing Transcription in Euk vs. BacBacteria:Sigma factor only found in bacteriaSigma factor binds onto the promoter_____________________________________________________________________________________- Promoters: region where DNA poly binds to to start transcription- In Euks and Archaea, the promoter has the sequence 5’ TATAAA 3’ - TATA box which serves as a protein binding site- Transcription takes place about 25 nucleotides downstream of the TATA box- Elongation occurs as RNA poly moves along template strand in the 3’ to 5’ direction- In bacteria, promoter recognition is identified by the sigma factor, which is a protein that associated RNA poly that facilitates its binding to specific promoters - Once transcription is initiated, the sigma factor dissociates and RNA poly continues transcription on its own
Eukaryotic transcription processRNA poly adds successive nucleotides to the 3’ end of the transcriptEnlongation: the process in which successive ribonucleotides are added to grow the transcript- occurs in both prokaryotes and eukaryotes once transcription initiation takes placeTranscription Bubble- 2 strands of DNA are separated - The growing end of the RNA transcript is paried with the template is paired with the template strand
In bacteria ,- transcription bubble is about 14 base pairs in length- region of paired RNA-DNA is in the bubble is about 8 base pairs in lengthSteps of polymerization reaction:1) Incoming ribonucleoside triphosphate is accepted by the RNA polymerase only if it is the proper base pair required 2) RNA polymerase orients the 3’ end of the growing end so that the 3’ oxygen can attach to the first phosphate- Oxygen takes an electron + bond breaks = energy3) A phosphate-phosphate group is released - This cleavage makes the polymerization reation irreversibleRNA polymerization complex is a molecular machine that opens, transcribes, and closes DNA- Transcription bubble forms inside of the of the RNA polymerase- Has channels for DNA input and output, nucleotide input, + RNA output- Disrupts the DNA double helix- stabilizes the DNA-RNA paired region- Restroes the DNA double helix - Transcribes with <1 mistake per 10,000 nucleotides- Does not have an error correcting function like DNA polymeraseSelf Assessment Qs
What are 4 differences between the structures of DNA and RNA? -1) sugar in RNA is ribose while the sugar in DNA is deoxyribose. 2) The base thymine is replaces by the base uracil in RNA. 3) DNA molecules are usually double stranded while RNA molecules are shorter and single stranded. 4) DNA molecules are very long while RNA molecules are very shortA segment of one strand of double-stranded DNA has the sequence 5’ ACTTTCAGCGAT 3’. What is the sequence of an RNA molecule sytnthesized from the DNA template?3’ AUCGCUGAAAGU 5’