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Week 5
Replication, transcription + translation
| Question | Answer |
|---|---|
| DNA vs. RNA | DNA: deoxyribose sugar, double stranded + T base RNA: ribose sugar, single stranded + U base |
| Explain flow of genetic information from the nucleus to the cytoplasm of the cell | Transcription in the nucleus (RNA strand is created); leaves through nuclear pores as mRNA, binds to ribosome in the cytoplasm; translation happens are protein is built |
| What are the 3 components of a nucleotide? | Pentose sugar, nitrogenous base + phosphate group |
| Purine. vs Pyrimidine | Purine: A, G (larger, 6 member ring fused to 5 member ring) Pyrimidine: C, T/U (smaller, 6 member ring) |
| Deoxyribose vs. ribose sugar | OH vs. H group on the 2' carbon position |
| What is the chemical reaction/bonds that join nucelotides together? | Phosphodiester linkage (dehydration synthesis) |
| What does 5' or 3' of a strand mean? | The direction of the DNA/RNA strand. New nucleotides are only added on to the 3' end |
| Why is the arrangement of the 2 strands in a DNA molecule said to be 'antiparallel'? | they run in oposite directions (one 5'-3' other one 3'-5') |
| What components of DNA form the backbone of the molecule and which ones face the centre of the double helix? | Phosphate groups + pentose sugar on outside/backbone, nitrgenous bases on inside |
| What kinds of chemical attractions hold the 2 strands in a DNA molecule together? | hydrgoegn bonds hold bases together |
| Which nitrogenous bases pair together and why in DNA? | C-G (3 hydrogen bonds) A-T/U (2 hydrogen bonds) complementry hydrogen bonds + optimal spacing between backbones |
| Why is DNA replication described as 'semiconservative' | Each new DNA helix is made with one of the old parent strands (1 new strand, 1 old strand) |
| What is a replication bubble? | Where DNA helicase seperates/"unzips" the 2 strands at the origin of replication. replication proceeds in both directions + there is a "replication fork" at each end |
| Prokaryotic vs. eukaryotic cells based on the number of origins of replication | prokaryote: 1 Eukayote: multiple |
| Helicase function (in DNA replication) | "unzips" DNA strands at the replication fork. requires ATP to break bonds in between bases |
| Primase function (in DNA replication) | needed to start replication. enzyme starts RNA chain from scratch (5-10 nucleotides long) complementry to the template DNA strand. starting point for the new DNA strand |
| DNA polymerase function (in DNA replication) | synthesizes leading strand in 5'->3' strand, assembles/adds complementry nucleotides to template strand |
| Ligase function (in DNA replication) | covalently joins okazaki fragments on the lagging strand into a continuous strand |
| What is a primer + why is it needed? | short single stranded nucleic acid sequence; provides starting point for DNA synthesis (nucleotides can only be added onto the 3' end of a strand |
| Why cant 2 strands of the new DNA molecule be synthesized in the exact same way? | DNA strands are antiparallel and nucleotides are added from 5' to 3', creating the leading and lagging strand |
| Explain synthesis of the leading strand | a continuous 5' to 3' DNA replication that moves towards the replication fork |
| Explain synthesis of the lagging strand | is synthesized in a sereies of short segments called Okazaki fragments away from the replication fork (5' to 3') |
| What are Okazaki fragments + why do they occur? | short discontinued DNA strands created on the lagging strand. joined together by DNA ligase |
| nucleic acid monomer + polymer names + the 2 major types of nucleic acids | Nucleotides + polynucleotides DNA + RNA |
| Know the whole lagging/leading strand/okizaki fragment/DNA ligase + helicase + polymerase + directions of everything diagram | not a card !! |
| Ribosomal RNA location + function | synthesized in nucleus (eukary); takes place in cytoplasm; makes up most of the ribosomes, joins together amino acids by peptide bonds (large subunit) by reading instructions from mRNA that goes through the small subunit of the ribosome |
| Transfer RNA location + function | located in cytoplasm; carries amino acids to the ribosome, passes through the ribosomes A, P + E sites adding amino acids to complement the mRNA strand; uses anticodon to read mRNA |
| Messenger RNA location + function | synthesized in the nucleus via transcription; carries the genetic info of DNA the the cytoplasm/ribosomes where its then translated to make proteins |
| Describe the genetic code | code used by all living organisms to make proteins; 3 letter "words"/64 codons that code for 20 different amino acids |
| Explain transcription | DNA strand seperates; 1 half is copied into a mRNA strand to transfer genetic info from the nucleus to the cytoplasm/ribosomes |
| Explain translation | the process of the mRNA strand being translated into an amino acid sequence on rough ER/ribosomes. has 3 stages; initiation, elongation + termination |
| Explain the role of mRNA, ribosomes, + tRNA in translation | mRNA: carries gen. info from DNA from nucleus to rib rib: the site of protein synthesis (translation) tRNA: brings the correct A.A to the rib. Each tRNA has a specific anticodon that matches with mRNA codon ensuring A.A. are added in correct order |
| Explain tRNA's 2 + 3 dimensional structure + role of base pairing | 2D - cloverleaf 3D - L shape anticodons can still bind successfully to a codon whose 3rd position requires a nonstandard base pairing allowing it to recognize multiple codons for the same animo acid |
| What is the minimum number of differernt subtypes of tRNA molecules it should have + how many does it actually have + why? | 20, but it has between 31-61+ to allow for the wobble effect + becuase multiple codons code for the same amino acid |
| Why do codons need to be triplets and not pairs of nucleotides? | triplets create the right amount of combinations, 2 would not be enough |
| What is the template strand of DNA? | the side of the DNA strand that gets read to create the complementry mRNA strand (transcription) |
| Why is the genetic code described as redundent but not ambiguous? | Redundent: 1 amino acid can be coded for by multiple codons Unambiguous: a codon will only code for 1 amino acid |
| What other codons does the genetic code have? | 60 code for amino acids, 3 are stop codons and one is a start codon (AUG) that also produces an animo acid |
| What is meant by "the genetic code is universal"? | almost all living organisms use/follow the same genetic code |
| What is the function of RNA polymerase? (direction of elongation, direction of movement along template, need of a primer, + DNA unwinding ability) | for transcription; synthesizes RNA strand in the 5' to 3' direction (goes along template strand in 3' to 5' direction); does not need a primer; can locally create a "transcription bubble" to expose the template strand |
| Describe initiation (in translation) | ribosome subunit binds to mRNA at the ribosome binding site; initator tRNA carries Met to start codon (AUG); large ribosome subunit binds, sandwiching mRNA between it + small subunit; tRNA in P site |
| What does the mRNA molecule produced during transcription "complementry" to the template DNA molecule? | It is complemently/an oposite base copy of the template DNA strand (substitutes T as U) |
| What are ribosomes made of + how mamy subunits does it have? | ~65% rRNA + ~35% ribosomal proteins. 2 subunits (large + small) |
| 3 steps of translation in the ribosome | initiation, elongation + definition |
| Describe elongation (in translation) | tRNA with an anticodon that matches the next mRNA codon binds to A site; peptide bond forms between amino acid in A site and polypeptide chain in P site; ribosome shifts mRNA 1 codon foward; tRNA in P moves to E, E leaves, A open again |
| Describe termination (in translation) | occurs when A site encounters a stop codon; protein called a release factor enters A site (resembles tRNA but does NOT carry an amino acid) breaks the bond linking the P site tRNA to the polypeptide chain releasing protein. ribosome subunits seperate |
| Translocation definition | the specific step in the elongation phase where the ribosome moves one codon down the mRNA |
Created by:
every_august
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