Introduction to the Human Genome Flashcards
In DNA nucleotides, what is the nitrogenous base attached to?
Attached to deoxyribose 5′-phosphate
Outline complementary base pairing.
- 2 hydrogen bonds between adenine and thymine
- 3 hydrogen bonds between cytosine and guanine
What stabilises the nucleotides and what binds them together?
- Sugar-phosphate backbone
- Phosphodiester bonds
What direction is DNA read in?
5’ to 3’
Outline DNA coiling
- Double helix coils around histones to form nucleosomes
- Nucleosomes coil to form solenoids to form chromatin loops
- Chromatin becomes condensed and forms chromosomes
Outline the central dogma of molecular biology
- TRANSCRIPTION - production of mRNA from DNA template
- TRANSLATION - synthesis of protein from mRNA
Outline the principles of the genetic code
- Read in triplets
- Codons encode an amino acid
- 64 possible combinations but 20 amino acids - code is degenerate
Define a gene
- Basic unit of inheritance - passed to offspring
- Regions that code for RNA
Outline the structure of the gene.
- Enhancer site regulating transcription
- Promoter region - TATA box in eukaryotes - RNA polymerase II binds upstream of first gene exon
- Start of codon - start of translation
- Also has UTRs
Define intron
Non-coding regions of a gene which are spliced out during
mRNA processing
Give examples of post-translational modifications
- Cleavage into smaller polypeptide units
- Combination with other polypeptides
- Glycosylation
- Acetylation
RELEVANT for function of protein - if a protein needs to become a glycoprotein, it will be glycosylated
Where does protein processing occur?
- Cytoplasm
- Golgi apparatus
What is the difference between tertiary and quaternary structure?
- TERTIARY - three dimensional folding due to side chain interactions
- QUATERNARY - occurs in proteins consisting of more than one amino acid chain
Outline the process of collagen fibril formation
- Pro-alpha polyppetide chain is formed and undergoes hydroxylation and glycosylation
- Three polypeptide chains assemble into triple helix and secreted out of cell
- Portions at each end of procollagen are cleaved, forming a mature molecule
- Form collagen fibrils
Describe osteogenesis imperfecta
- Caused by mutations in gene encoding type 1 collagen
- CLINICAL FEATURES - recurrent bone fractures, short stature and scoliosis
- Subsitution of glycine to another amino acid
- Glycine sits in centre of triple helix structure –substitution leads to instability
Define mitosis
- Cell division in which two genetically identical diploid cells form
- Involves interphase, prophase, metaphase, anaphase, telophase and cytokinesis
Define meiosis
Formation of haploid gametes from diploid cell
Outline steps in meiosis.
- INTERPHASE I - replication
- PROPHASE 1/METAPHASE 1 - pairs of homologous chromsomes line up at centre of cell - crossing over at chiasmata and exchange genetic material
- MEIOSIS I - REDUCTION DIVISON - 1 cell forms 2 cells with 1 chromosome
- Meiosis II – sister chromatids segregate - get 1 chromatid in each cell
Outline the process of DNA replication. PART 1
- Helix unwound using topoisomerase
- Hydrogen bonds between bases break (helicase enzyme)
- Single DNA strands – become templates
- DNA polymerase travels along DNA strand adding free nucleotides from 5’ to 3’ end
Outline the process of DNA replication. PART 2
- Whole length of DNA strand replicated = replication fork
- Newly added nucleotides checked to make sure complementary to base
- If not – nucleotide excised and replaced with correct nucleotide
- When DNA replication error not successfully repaired = mutation
Outline the process of DNA repair
- DNA repair enzymes recognise altered base
- Excise by cutting DNA strand (endonuclease)
- Replace with correct base (using complementary base-pairing) –DNA polymerase
- Re-seal DNA backbone - DNA ligase
What causes genetic variation?
- Crossing over
- Mutations
- Random fertilisation
