Molecules, genes and disease (role of genes) Flashcards
Describe the different types of intermolecular bonds
Hydrophobic bonding: Entropy driven, non polar molecules come together to exclude water
Hydrogen bonds: Between a lone electron pair and a positive hydrogen atom.
Ionic bonds: between charged ions, eg. carboxyl and amino groups
Van Der Waal’s forces: A brief partial charge on all atoms induces an attraction.
Describe the basic structure of DNA and RNA
DNA monomer units are made up of nitrogenous bases of which there are 5, 2 purines A & G and 3 pyrimidines C, T U.
Purines: A & G consist of two rings and a re present in both DNA and RNA.
Pyrimidines: C, T, U consist of a single ring structure all exist in DNA and RNA except U which is only found in RNA as a replacement to T.
Between A-T there are 2 hydrogen bonds so weaker that between G-C where there are 3 hydrogen bonds.
DNA is formed of two anti-parallel strands held together by hydrogen bonds between bases. Forming a double helix structure. They formed as sugar phosphate backbones with bases attached. Always written in the 5’-3’ direction.
1’ is always where the nitrogenous base is attached on the sugar then move around clockwise to 5’ where the phosphate is attached. At 3’ there is a hydroxyl group that the next phosphate attaches to. The phosphate and the hydroxyl group join together via a phosphodiester bond.
There are 10 bases per turn in the double helix, with major and minor grooves.
Nucleotide- base, sugar, phosphate
Nucleoside- base and sugar
The sugar is ribose in RNA and deoxyribose in DNA.
DNA is double stranded unlike RNA which is single stranded and so can leave the nucleus and DNA can’t. DNA is a double-stranded molecule with a long chain of nucleotides, while RNA is only single-stranded in most of its biological roles and has a shorter chain of nucleotides (after transcription and splicing, only exons remain in RNA). DNA exists mainly in a double helix form while RNA will take on many different shapes and sizes such as the ‘hair pin formation’. DNA is used to carry an organism’s genetic information while RNA takes on many different roles, for instance, RNA can act as an enzyme such as ribozyme. There is one single type of DNA while there are many types of RNA that have different functions such as mRNA (carries DNA message to cytoplasm), tRNA (carries amino acids to mRNA and Ribosomes), rRNA (Ribosomal RNA, workbench for protein synthesis). DNA cannot catalyze its own synthesis while RNA can. This supports the RNA World Hypothesis. The pairing of bases in DNA including A-T(Adenine-Thymine) and G-C(Guanine-Cytosine)is different to that of RNA including A-U(Adenine-Uracil) and G-C(Guanine-Cytosine).
Both DNA and RNA starts synthesis in the 5’-3’ direction. However, no primer is needed for RNA. In addition, RNA polymerase lacks the ability to detect errors of base pairing, a trait that DNA polymerase is capable of doing.
Describe the process of DNA replication- 3 phases
Initiation:
Elongation:
Termination:
Describe the process of DNA folding
In order to fit the vast amount of DNA into the nucleus of a cell it associates with histone proteins to fold it. Histone is is positively charged and interacts with negative phosphate charge on backbone DNA.
The DNA first wraps twice round the histone protein core (which is an octomer of 8 proteins) forming nuclesomes that produces a bead on a string like structure. This is called Euchromatin which is transcriptionally active.
Heterochromatin can then be formed in which the euchromatin folds in on its self forming a 30nm solenoid fiber. It is transcriptionaly inactive as the genes are bound too tightly.
Inheritance patterns
Genes vs alleles: a gene refers to a region of DNA that encodes a protein. An allele is one of many versions of a gene, of which a genotype consists of two copies (generally). Genotype is the genetic makeup of the individual the phenotype is the physical characteristics expressed due to the genotype. (influnced by the environment).
Autosomal vs sex linked: autosomal inheritence involves the 22 autosomes while sex linked inheritance involves the sex chromosomes X or Y.
Dominant vs recessive: dominant allele is one that appears in the phenotype of a heterozygote, but rather is masked by a dominant allele.
The locus is the position of the gene on a chromosome.
Co-dominance:when both alleles in the geneotype contribute to the phenotype
Complementation: multiple genes are involved in producing a phenotype. Each parent can be deficient in different genes, but in the genotype of the offspring each deficient allele can be complemented to produce a normal phenotype.
Linkage:Genes are linked when they are found on the same chromosome and so during recombination they can stay together. The further away they are the less likely they are to move together.
What is the difference between pre m-RNA and RNA?
pre m-RNA contains both introns and exons, whereas mature m-RNA contains just exons.
What is the difference between pre m-RNA and RNA?
pre m-RNA contains both introns and exons, whereas mature m-RNA contains just exons the coding region. This difference occurs during RNA splicing when the introns are removed allowing one long continuous piece of m-RNA with only exons. They are removed by the splicesome complex.
Describe the process of translation
The process of translating the mature m-RNA into a polypeptide sequence.
Requires ribosomal subunits either free in cytoplam or at the rough ER.
Initiation: Small ribosomal subunits associate with mRNA and move to the start codon. Methionine (AUG) binds the larger subunit completes the complex.
Elongation and Translocation: Amino-acyl tRNA binds to the codon at the A site and the amino acid at the T site forms a peptide bond with it. Through translocation the first tRNA exits via the E site and the ribosome moves along the mRNA.
Termination: Once the stop codon is reached no amino acid blinds and the complex dissociate, releasing the polypeptide for completion of folding and modification.
Types of mutation/ repair
Can expand on these notes if I have time.
The genetic code is read in triplets the codon. Provides a reading frame. If a codon is altered it affects the reading frame.
Insertion
Deletions
Frameshift
Silent: no affect on the amino acid code
non sense: lead to the insertion of a stop codon.
missense: change in the amino acid
Chromosomal Abnormalities
Aneuploidy- Abnormal number of chromosomes (occur through non-disjunction events in meiosis can lead to trisomy, monosomy).
Polyploidy- an entire new set of chromosomes (multiple of the haploid number).
Alterations in genes that can lead to cancer
Proto-oncogenes: wild-type genes involved in cellular growth and proliferation. Encode for things like growth factors and growth factor receptor. Promote progression through the cell cycle, regulated.
Oncogenes: Mutant proto-oncogenes which have undergone a gain-of-function mutation and act dominantly. Promote progression through the cell cycle and are implicated in caner progression.
Tumour-suppressor genes: wild-type genes which act to inhibt progression through the cell cycle. Undergo loss-of-function mutation and require both alleles to be mutated to contribute to cancer progression.
