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Description
Flashcards by Diana Domingues, updated more than 1 year ago
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Created by Diana Domingues
over 6 years ago
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| Question | Answer |
| What are DNA and RNA composed of? | A pentose sugar A phosphate group A nitrogenous base |
| 4 nitrogenous bases of DNA | Guanine Adenine Thymine Cytosine |
| 4 nitrogenous bases of RNA | Guanine Adenine Uracil Cytosine |
| Purines | Two rings Adenine and Guanine |
| Pyrimidines | One ring Thymine and Cytosine |
| Bond linking nucleotides | Phosphodiester bond (covalent) |
| Phosphodiester bond | Formed between the phosphate group attached to the 5'C of one sugar and the hydroxyl (OH) group attached to the 3'C of another sugar |
| Differences between DNA and RNA | - DNA contains deoxyribose - Bases are A, G, T, C - A double stranded molecule - One type of DNA (compared to 3 types of RNA) |
| Bonds between G and C | 3 hydrogen bonds |
| Bonds between A and T | 2 hydrogen bonds |
| Strand direction | DNA strands are antiparallel to each other. One in 5' to 3', the opposite in 3' to 5'. |
| Replication | The copying of DNA to produce two identical DNA molecules. Occurs during the S phase of the cell cycle. It is semi-conservative |
| Semi-conservative | Each daughter molecule formed contains one original strand from the parent molecule and one newly synthesized strand |
| Transcription | The process which the information in a strand of DNA is copied into a new molecule of mRNA. |
| Sense strand | DNA strand that is not transcribed. Has the same sequence of bases as the mRNA molecule |
| Antisense strand | DNA strand that is transcribed Complementary to the mRNA molecule |
| mRNA molecule | Forms the template for protein synthesis Upon leaving the nucleus, it will bind to one or several ribosomes and allowed the translation process to begin. |
| Codon | 3 bases on the mRNA strand. Each codon is translated into one amino acid in a polypeptide chain |
| Genetic code is degenerate | Some amino acids are encoded by more than one codon |
| Polymerase Chain Reaction | Technique used to amplify DNA. Uses cycling heating and cooling of a DNA sample in the presence of primers, DNA nucleotides and Taq polymerase |
| Taq polymerase | A DNA polymerase isolated from Thermus Aquaticus bacterium. Thermostable, which is required to withstand high PCR temperatures. |
| Transgenic organism | Placing a gene from one organism into a different organism due to the universality of the genetic code. |
| Meselson and Stahl | Demonstrated how DNA replication progresses in a semi-conservative way. Used E.Coli bacteria and 15N and 14N. |
| Eukaryotic DNA | Acidic and negatively charged.. Associated with histones. Prokaryotic DNA is not associated with histones, hence it is described as naked DNA |
| Histones | Basic and negatively charged. Neutralise the DNA when they bond |
| Nucleosome | A length of DNA of about 150 base pairs, wrapped around a core of eight histones and bound with H1 histones. |
| Uses of nucleosomes | - Help supercoil the DNA while still ensuring appropriate access - Neutralises the DNA |
| Stability of double helix | - Hydrogen bonding between purines and pyrimidines - Slightly positive charge on T, slightly negative charge on A |
| Initiation of DNA replication in eukaryotes | Can be initiated at various points, but can only be started on one position on prokaryotic DNA, Ensures a faster and more efficient DNA replication in eukaryotes. |
| Rate of replication | 100 nucleotides per second in eukaryotes 1000 nucleotides per second in prokaryotes |
| Helicase | Binds to the origin of replication and breaks the hydrogen bonds to unwind the DNA double helix. |
| Single-stranded binding proteins | Bind to the single stands formed to keep them apart allowing time for the DNA sequence to be copied. |
| DNA Gyrase | Relieves the supercoiling and tension on the region ahead of the helicase |
| Energy for replication | As deoxynucleoside triphosphates bind to the template strand, they lose their two extra phosphate groups to generate energy (used to bind the nucleotides to the polynucleotide chain) |
| Leading strand | Replicated continuously in the 5' to 3' direction by DNA polymerase III |
| Lagging strand | Replicated discontinuously in small fragments in the 5' to 3' direction by DNA polymerase III |
| DNA Primase | On the lagging strand, it makes short RNA primers which allow the DNA polymerase III to add deoxynucleotides to the RNA primer. |
| DNA polymerase I | Removes the RNA primers from the lagging strand and substitutes them with short DNA segments. |
| DNA ligase | Joins the Okazaki fragments together in the lagging strand |
| Non-coding DNA | Accounts for more than 98% of the human genome. They're DNA sequences within a genome that's not protein coding |
| Non-coding DNA regions | - Regulators of gene expression - Introns - Telomeres - Genes for tRNAs |
| Regulators of gene expression | Eg. Promoters are sequences that occur just before genes and can act as a binding point for the RNA polymerase enzymes that catalyst the transcription process Other eg.'s include enhancers and silencers |
| Introns | DNA base sequences found within genes that get removed at the end of transcription. Hence, they do not contribute to the amino acid sequence of the polypeptide made from the gene. |
| Telomeres | Repetitive sequences that protect the ends of the chromosome. |
| Tandem repeats | Sequence of 2 or more DNA base pairs that is continuously repeated. They form part of the non-coding DNA. Used for identification purposes at a crime scene |
| DNA Sequencing | Method used to deduce the order of the nucleotides. |
| Rosalind Franklin | Carried out X-ray diffraction experiments leading to the determination that DNA was a helical molecule. |
| Hershey and Chase | Proves that DNA was the genetic material, instead of proteins as it was thought at the time. |
| Transcription | The synthesis of mRNA |
| RNA polymerase | Starts near a region of the gene called the promoter. |
| Initial part of transcription | RNA polymerase binds to the DNA and causes the double helix to unwind. |
| RNA nucleoside triphosphate | RNA nucleoside triphosphates are added to the growing mRNA chain |
| Post-transcriptional modification of mRNA | The mRNA needs to be prepared for translation - the introns are sliced out by a spliceosome. A cap and a poly (A) tail are added. |
| Enhancers | Activator proteins bind there to increase the rate of transcription |
| S | Repressor proteins bind there to decrease the rate of transcription |
| Acetylation | Tails of histones can be acetylated. This means adding an acetyl group preventing binding between nucleosomes. This partially unwinds the DNA, allowing RNA polymerase to access it. |
| Methylation | Tails of histones can be methylated. This means adding a methyl group, usually causing the gene not to be expressed |
| Epigenetics | The study of heritable changes in organisms that are brought about by changes in gene expression rather than the modification of the genetic code |
| Translation | Protein synthesis - mRNA is decoded to produce the specific sequence of amino acids in a polypeptide chain, |
| S | Mature mRNA binds to a small ribosomal subunit at the mRNA binding site. The mRNA start codon AUG is linked to the initiator tRNA carrying methionine |
| Initiation | mRNA, small ribosomal subunit, initiator tRNA and large ribosomal subunit assemble to form the translation complex |
| A, P, E binding sites stands for... | Aminoacyl-tRNA binding site Peptidyl-tRNA binding site Exit site |
| A site | Where incoming tRNA with its attached amino acid binds |
| P site | Where tRNA from the A site moves to after forming a peptide bond with the growing polypeptide chain. |
| E site | Where tRNA moves to after transferring its amino acid to the growing polypeptide chain, ready to be released by the ribosome. |
| S | U |
| tRNA structure | Single-stranded RNA molecule that folds on itself to form a typical clover-leaf-shaped structure with double-stranded regions held together by hydrogen bonds and 3 hairpin loops. |
| Anticodon | Contained by one of the loops on tRNA, which can bind to an mRNA codon |
| Amino acid | Each tRNA has its specific amino acid attached at the 3' end of the CCA. This is transferred to the growing polypeptide chain by forming peptide bonds |
| Proteins translated by free ribosomes | Destined to function within the cell. Once mRNA moves in the cytoplasm, ribosomes attach to it and translation begins |
| Proteins translated by bound ribosomes | Destined to function in lysosomes or secreted outside the cell. The beginnings of the polypeptide contains a signal sequence recognized by a signal recognition particle. The SRP binds to the SRP recognition protein on the ER, allowing the polypeptide to enter the rER. Post-translational modification take place in the lumen of the rER. |
| P | A structure occurring when multiple ribosomes attach to the same mRNA strand |
| Primary structure | The sequence and the number of amino acids in the polypeptide. Maintained by peptide bonds between the subunits |
| Secondary structure | Formed when the polypeptide chain folds back on itself into alpha helices or beta pleated sheets. Stabilised by hydrogen bonds between -NH groups and -C=O groups from the peptide bonds. |
| Tertiary structure | Further folding of the polypeptide. Stabilised by interactions between R groups. Eg. Ionic, covalent (eg. disulphide bridges) and hydrogen bonds, as well as hydrophobic interactions between non-polar amino acids |
| Quaternary structure | Exists in proteins with more than one polypeptide chain. Subunits are joined together by similar bonds to that of the tertiary structure. Also have a non-protein molecular unit (a co-factor or a prosthetic group) |
| Conjugated protein | A protein with a prosthetic group |
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