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SBI4U
SBI4U / Molecular Genetics
| Question | Answer |
|---|---|
| Who introduced the double helix model? | James Watson and Francis Crick |
| Qualities of the double helix | - antiparallel - double-stranded - right-handed |
| Purpose of the prime marks? | - to distinguish between the C atoms of the sugar from the ring atoms of the nitrogenous base - the numbers given to atoms of nitrogenous bases DO NOT have prime symbols |
| DNA Helicase | unwinds the DNA double helix by breaking the H-bonds |
| What is the function of single stranded binding proteins? | act as a barrier to prevent the strands of DNA double helix from joining back together |
| DNA exists in _________ molecules | circular |
| What is a genome? | the complete set of DNA (genetic material) in an organism |
| A typical human chromosome is ______________ nucleotides long, which would be _____ long if linear | 300 million nucleotides 5 cm |
| Why does DNA have a negative charge? | due to the abundance of phosphate groups. This helps it to bind with a positive protein complex called a histone. |
| What is a tumour? | an unregulated growth of cells |
| Somatic cells | any cell of a living organism other than the reproductive cells |
| Stem cells | unspecialized cells that can divide limitlessly to produce multiple cells of various types |
| What is a gene? | the basic unit of heredity passed on from parent to offspring |
| Functions of RNA | |
| Is DNA stable under alkaline conditions? | Yes! |
| Propagation of DNA/RNA | DNA is self-replicating, while RNA is synthesized from DNA on-demand |
| How does uracil differ from thymine? | uracil lacks a methyl group on it's ring |
| During which phase does DNA rep. occur? (cell cycle) | the vast majority of DNA synthesis occurs in the S phase, and the entire genome must be unwound and duplicated to form two daughter copies |
| What is a histone? | - a protein that provides structural support for chromosomes - positively-charged protein - play a role in the regulation of gene expression - rich in arginine and lysine residues |
| ___ histone proteins come together to form a nucleosome | 8 |
| What are plasmids? | smaller circular sections of DNA found in the cytosol of bacteria; replicates independently of chromosomal DNA |
| Semiconservative replication | a mechanism of DNA rep. in which each of the two strands of parent DNA is incorporated into a new double-stranded DNA. |
| DNA Helicase | replication enzyme that separates and unwinds the DNA strands |
| Replication Fork | the point of separation of the two parent DNA strands during replication |
| Single-Strand Binding Proteins | replication enzyme that prevents parent DNA strands from annealing to eachother once they have been separated by helicase |
| Okazaki Fragments | the pieces of new DNA on the lagging strand |
| RNA primase | replication enzyme that produces RNA primers |
| RNA primer | replication molecule that acts as a starting point for replication |
| DNA Polymerase III | replication enzyme that builds new DNA strands from nucleotides |
| Leading strand | the DNA strand that is copied in the direction of the replication fork |
| DNA Polymerase I | - replication enzyme that fills in the gaps between Okazaki fragments - proofreads the final strands |
| DNA ligase | enzyme that catalyzes the formation of phosphodiester bonds between Okazaki fragments |
| DNA Polymerase II | replication enzyme that repairs any damage to DNA, including damage between replication events |
| DNA Gyrase | works in the area ahead of the replication fork to prevent supercoiling |
| Types of RNA | - messenger RNA (mRNA) - transfer RNA (tRNA) - Ribosomal RNA (rRNA) |
| Role of mRNA | carries info from the DNA in the nucleus to ribosomes in the cytoplasm |
| Role of rRNA | - make up over 60% of the ribosome weight - |
| Role of tRNA | - carries amino acids to the ribosome during translation to help build an amino acid chain - a molecular "bridge" between mRNA codons and the a.a's they encode |
| How can changes in DNA occur? | - sexual recombination - genetic recombination - mutations |
| What is a nucleosome? | - a unit of DNA storage consisting of 8 histones with DNA strands wrapped around them - a single nucleosome consists of 150 base pairs wrapped around histones |
| What are solenoids? | a group of 6 nucleosomes |
| What is supercoiling? | - the continuous twisting of prokaryotic DNA that reduces the volume of the DNA - greatly reduces the space and allows for more DNA to be packaged |
| What are telomeres? | repeating sequences of DNA at the end of a chromosome that protects coding regions from being lost during replication |
| Central Dogma of Biology | DNA → RNA → protein |
| Exonuclease | enzyme that cuts out nucleotides at the end of a DNA strand |
| How can DNA be repaired upon any damage? | - direct reversal; some reactions can be "undone" by enzymes in the cell - excision repair; fixed by the removal and replacement of the damaged region - double-stranded break pair; repair double-stranded breaks in DNA |
| In which direction does DNA polymerase add nucleotides? | 5' → 3' direction |
| Cell Senescence | cell aging; when a cell loses its ability to divide and grow |
| Hayflick Limit | the total number of times that a normal cell can divide |
| Given that there are lots of nitrogenous bases, why is DNA considered an acid? | - the basic properties are offset since they can H-bond with each other - when the phosphate groups are protonated, they are acids |
| Chargaff's Rules | - A, T, C, and G were not found in equal quantities - amounts of bases varied among species, but not between individuals of the same species - amount of A = T, amount of C = G |
| Post-Transcriptional Modifications | - addition of a 5' cap and a 3' poly-A-tail. This increases mRNA stability - Splicing; introns are chopped out and exons are stuck together. This gives mRNA the correct sequence |
| What is the promoter region? | a region of DNA where RNA polymerase begins to transcribe a gene |
| What is the start codon? | AUG (methionine) |
| What are the stop codons? | - UGA - UAG - UAA these tell the cell when a polypeptide is complete |
| Insertions | when new nucleotide pairs are inserted in the midst of a gene |
| Deletions | when nucleotide pairs are removed from a gene |
| The template strand for mRNA synthesis is always in which direction? | 3' → 5' |
| In a chromosome, it has a ratio of ___ DNA to ___ protein | 40% DNA to 60% protein |
| What are chromosomes? | - threadlike structures made of protein and a single DNA molecule - reside in the nucleus - humans have 22 pair of autosomes and one pair of sex chromosomes for a total of 46 |
| Which biological gender have two X chromosomes (XX) | females |
| Which bases have two rings? | purines |
| What type of base is uracil? | pyrimidine |
| When the mice wee injected with a live S strain in Griffith's experiment, what happened? | - mice developed pneumonia and died within a matter of days - S-strain bacteria were highly virulent |
| Does the promotor gets transcribed in transcription? | no |
| What characteristic pattern is observed in promotor regions? | base-pair pattern rich in A's and T's |
| What is the promotor? | a region that indicates where and which gene to transcribe in DNA |
| Is a primer required for RNA polymerase to function? | no |
| What is a primer? | a short nucleic acid sequence that provides a starting point for DNA synthesis |
| A terminator sequence is... | a section of nucleic acid sequence that marks the end of a gene during transcription |
| Why is a 5' cap necessary for mRNA? | - protects the mRNA from digestion by nucleases and phosphates as it exits the nucleus and enters the cytoplasm - initiates translation |
| Which enzyme adds the poly-A-tail? | poly-A-polymerase enzyme |
| Why is a poly-A-tail important? | protects the mRNA transcript from degradation |
| Introns are __________ regions of a gene | non-coding |
| Difference between Thymine & Uracil | thymine has a methyl group on its 1' carbon, while uracil does not |
| Where does the ribosome start polypeptide production? | at the 5' cap of the mRNA (initiation) |
| What is the reading frame? | the phase of adding amino acids to the polypeptide |
| Role of the release factor? | recognizes that the ribosome has stalled and aids in the release of the polypeptide chain |
| Why is gene regulation important? | an important control mechanism that the organism must use in order to turn genes on when they are required and off when they are not |
| What are the four levels of gene regulaton? | - transcriptional - post-transcriptional - translational - post-translational |
| What is post-transcriptional gene regulation? | - mRNA is modified in the nucleus before translation - splicing; introns and exons are removed |
| What is transcriptional gene regulation? | regulates which genes and at what rate transcription occurs |
| What are the possible effects of a point mutation? | 1- may not alter the a.a. sequence since one a.a. may be encoded by several different codons 2- may code for a.a. that's functionally similar to the original 3- may code for a functionally different a.a. 4- may produce a stop codon |
| How many telomere base pairs are lost per replication? | ~100 |
| In humans, a cell can replicate roughly ___ times before cell senescense | 50 |
| Germ line cells | - gametes (sperm and ova) and the stem cells that divide to produce gametes - germline cells can divide via mitosis to maintain the diploid chromosome number |
| Haploid cells (n) | - possess one set of chromosomes (one gene for each trait) - in humans, n = 23 - in humans, gametes (sex cells) are haploid - produced in meiosis |
| Diploid cells | - two sets of chromosomes - in humans, 2n = 46 - in humans, all somatic cells are diploid - produced in mitosis |
| How is genetic material preserved in germline cells? | - these cells cannot tolerate any loss of genetic info; must maintain genetic integrity from parent to offspring - telomerase adds more DNA to the shortening telomeres, continually restoring their length |
| What are the starting points of DNA replication? | replication origins; helicase binds to these origins to begin unwinding the double helix |
| Replication bubble | when DNA is separated in both directions during replication |
| What is the energy source needed to power DNA polymerase reactions? | energy is provided by phosphate groups attached to the nucleoside molecule |
| Solenoids | - a condensed chromatin fibre - helps package eukaryotic DNA into the nucleus - a group of 6 nucleosomes |
| Importance of supercoiling | - reduces the volume of DNA (compacting) - required for DNA/RNA synthesis |
| Chromatin | - a mixture of DNA and proteins that form the chromosomes - can unwind for DNA replication/transcription |
| How many base pairs make up a single nucleosome? | 150 |
| How many coils of DNA wrap around a nucleosome? | 2 |
| Why do we die from cancer? | if cells are continuously stuck in mitosis, they are likely not able to return to interphase to perform regular processes |
| What make nucleic acids acids? | - the phosphate groups - DNA is typically drawn with - charges because it is so acidic that if you put it in a neutral solution, its going to lose its H's |
| How is genetic info stored in a DNA molecule? | within the complementary base pairs |
Created by:
AAnani