Notes : 2.5 - 2.8 + 2.11 + 2.15 + 2.16 - DNA & Genetics Flashcards
What are the three components of nucleotides?
A pentose sugar (either ribose or deoxyribose), attached to a phosphate group and an nitrogen-containing base (either adenine, guanine, cytosine, thymine or uracil).
Describe the structure of DNA.
Double stranded. Made up of deoxyribose mononucleotides, linked through condensation reactions.
Possible bases are A,C, G and T. C pairs with G, A pairs with T.
How does DNA form a double stranded helix?
Bases on the nuclei acid strand form hydrogen bonds with each other, holding the two strands together.
• Stacking of many mononucleotides results in a helix (twisted) shape.
Describe the structure of RNA.
Single stranded. Made up of ribose mononucleotides, linked through condensation reactions. Possible bases are A,C, G and U. C pairs with G, A pairs with U.
How is the DNA sequence converted into proteins?
- Transcription; reads DNA sequence and produces mRNA.
- Translation; reads mRNA sequence and produces proteins.
What are Nucleic Acids
Nucleic acids are long chains (polymers) of lots of nucleotide monomers joined together by phosphodiester bonds. Thats why its called (DNA - deoxribose nucleic acid as dna is made up of lots of nucleotides joined together) - aka a nucleic acid.
What can nucleotide’s be split into.
1 - Mononucleotide (Consisting of one base,phosphate group and sugar).
2 - Dinucleotide ( Double so it will have 2 bases)
3 - Trinucelotide (Trinucleotide so will have 3 bases)
Poly - Many nucleotides.
Outline the process of transcription.
DNA uncoils into two strands with exposed bases. One used as a template.
An enzyme called RNA polymerase attaches to the start of the gene. (This is called the promoter region which signals to the RNA polymerase that this is where of the process of the transcription should start).
- RNA polymerase(Il) separates the DNA strands, producing a single DNA template for transcription.
- RNA polymerase joins the RNA nuclotides by forming phosphodieseter bonds between them
What is the promoter region ?
The promoter region is a regulatory region which does not code for amino acids but facilitates the process of transcription by helping RNA polymerase bind to the gene.
Name some differences between DNA and RNA
- the pentose sugar in DNA is deoxyribose and in RNA is ribose. The difference is that deoxyribose has one less oxygen atom.
- RNA contains uracil instead of thymine
- DNA is double-stranded whereas RNA is single-stranded
Explain the detailed version of DNA synthesis.
- Initiation: Enzymes called DNA helicases unwind and separate the two strands of the DNA double helix, forming a replication fork.
- Primer Binding: Primase an enzyme, synthesises short RNA primers at the replication fork. These primers provide a starting point for DNA synthesis.
- Leading Strand Synthesis : DNA polymerase attaches to the leading strand. is synthesized continuously in the 5’ to 3’ direction toward the replication fork. DNA polymerase continuously adds nucleotides to the growing leading strand. following the base-pairing rules (A with T, C with G).
- Lagging Strand Synthesis : The lagging strand is synthesised discontinuously in short fragments called Okazaki fragments. Primase synthesizes RNA primers for each Okazaki fragment, and DNA polymerase then adds nucleotides to each fragment, creating short DNA segments.
- Okazaki Fragment Processing : The RNA primers in the Okazaki fragments are replaced with DNA by DNA polymerase. DNA ligase joins the adjacent Okazaki fragments, sealing any gaps in the DNA backbone.
- Termination : DNA synthesis continues until the replication fork reaches the end of the DNA molecule. The newly synthesized DNA strands separate, and the process is complete.
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Types of RNA:
- Blurt everything you know about mRNA
Messenger RNA (mRNA)
o Produces during transcription – RNA polymerase uses DNA as a template to provide mRNA strand
o Carries the genetic code from the nucleus to the cytoplasm – provides the instructions for making a protein on the ribosome in translation
o Read in triplets.
Summarise the process of DNA replication.
- Double helix unwinds and the hydrogen bonds break, catalysed by DNA helicase.
- Complementary base pairing occurs between the template strand and free nucleotides.
- The nucleotides are joined by phosphodiester bonds, catalysed by DNA polymerase.
Explain the process of transcription.
- RNA polymerase binds to the beginning of a gene in an area known as the promoter region.
- RNA polymerase separates the DNA strands, producing a single DNA template for transcription.
- As RNA polymerase moves along one of the DNA strands (the template strand), it adds complementary nucleotides and connects them through the formation of phosphodiester bonds.
4.The other strand is referred to as the coding strand and will have an identical sequence to the newly synthesised RNA, except for the presence of thymine instead of uracil.
- Eventually RNA polymerase will reach a stop codons. A molecule of messenger RNA (mRNA) has been formed which will leave the nucleus and enter the cytoplasm.
What are promoter regions ?
The promoter region is a regulatory region which does not code for amino acids but facilitates the process of transcription by helping RNA polymerase bind to the gene.
Explain the process of translation.
- Once in the cytoplasm, the messenger RNA finds its way to structures called ribosomes.
- The ribosome attaches itself to the mRNA and slides along it (this is known as translocation). The ribosome ‘reads’ the mRNA in a series of three bases (such as AUG, CCA, GCU) called codons. Each codon corresponds to a particular amino acid.
- As the ribosome reads the codons, a transfer RNA (tRNA) molecule which has a complementary anticodon carries an amino acid to the ribosome. Once the ribosome has read through the length of the mRNA, a series of different amino acids will have been dropped off by several tRNA molecules.
- The ribosome catalyses peptide bond formation (condensation reaction) between the amino acids to form a polypeptide.
Blurt everything you know about the structure of tRNA molecules.
- tRNA molecules have an usual clover-shaped structure, formed by a single RNA strand folded over on itself through hydrogen bonding.
- At one end of the molecule, there is an amino-acid binding site and at the other there is an anticodon which contains a complementary base sequence to the mRNA codon.
How was the Meselson and Stahl’s experiment carried out ?
They used a heavy isotope of nitrogen (N-15) which has an extra neutron compared to the normal, lighter form of nitrogen (N-14).
They grew bacteria in the presence of the heavy nitrogen and any new DNA that the bacteria made would incorporate this isotope and so would weigh heavier. If DNA replicates conservatively, Meselson and Stahl knew that they’d see some DNA made of just heavy nitrogen with the rest made of only light nitrogen, but if it replicated semi-conservatively it would be a mixture of the two isotopes.
