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Flashcards in Molecular Biology Deck (168)
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What is the structure if DNA?

- 2 helical antiparallel polynucleotide chains
- 4 nucleotide bases
- The molecular struture males replication very reliable
- Structural errors are very rare


What can form if structural errors in DNA occur?

Although very rare, if DNA structural errors occur can cause mutations in the neurofibramin tumour mutations in the neurofibramin tumour suppressant gene causing neurofibromatosis


What is semi conservative replication?

How DNA replicates - each double helix is formed from one parental strand and one newly synthesised one


What are the steps in semi conservative replication?

1. Strands are separated by DNA helicase forming a replication fork
2. DNA polymerase synthesises new strands but can only occur in the 5' to 3' to ensure that the stands are antiparallel
3. The leading strand can be synthesised as it goes from the 5' to 3' end. However, the lagging strand cannot as it goes fro 3' to 5'. Other fragments called Okazaki fragments are used to fill the gaps
4. DNA ligase covalently links fragments together


What is the role of RNA in DNA replication?

- DNA polymerase can not synthesise a new chain from scratch
- So a RNA polymerase called DNA primes is used to synthesis a RNA primer
- Each primer is then extended by DNA polymerase
- Primer removed by ribonuclease H which results in a gap at the 3' end - filled in by DNA polymerase


What is the role of single stranded binding proteins (SSBs)?

Maintains the unwound parental DNA strands in a single-stranded conformation to ease replication fork progression


What are the essential features of the prokaryotic gene transcription process?

- RNA polymerase binds to the DNA sequences in the promotor region
- Transcript elongation - formation of mRNA
- RNA polymerase encounters terminator region - dissociates and transcription stops


What is the limiting factor of transcription?

Limited by the frequency of initiation


What are the essential features of the eukaryotic gene transcription process?

- RNA polymerase binds to the promotor region
- Elongation - transcripts of eukaryotic genes have exons (present in mRNA) and introns (spliced out) and does not appear in mature RNA
- Termination


What is a genome, transcriptome and proteome?

Genome - the entire DNA sequence in an organisms chromosome
Transcriptome - Entire set of RNA in a particular cell type
Proteome - Entire proteins in a particular cell type


What is a centromere?

- Repetitive DNA sequence to which mitotic spindles attactches via the kinetochore (provides insertion points for microtubules )
- Complex array of repeated DNA sequences


What is the replication origin?

DNA sequence where DNA replication is initiated
- Does not occur at the end - occurs in the middle and forms 2 replication forks


What is a telomere?

- Specialised DNA sequences at the end of chromosomes which maintains its integrity
- Telomerase creates a long 3' overhang which is repeated cases - protects the ends of DNA sequences


How does the E.coli genome compare to more complex organisms?

- E.coli - 4000 genes compressed into a singular circular DNA molecule
- Human genome is 5 times larger
- The more complex the organism the less densely packed they are but the larger the genome


What is different about the genomes of complex organisms in eukaryotic cells?

The more complex the organism the larger the introns (exons are the same)
- eg. The human Huntingtin gene is 7.5 times larger than in the pufferfish due only yo the increased size of introns


What percentages of sequences are up the human genome?

- 1.5% exons
- 50% repeated sequences
- 30% unique sequences - cause genes to become active


What is Mendel's definition of genes?

Discrete physical entities that fuction independently of one another to determine physical characteristics


Outline Mendel's experiment for his first law

- Pea plants that grew from smooth peas always produced smooth peas
- He cross breaded smooth pea plant with wrinkled and all offspring were smooth
- Offspring were self fertilised and there was a 3:1 of wrinkled and smooth peas
- Concluded there must be two copies of each gene - alleles
- and that smooth was dominant and wrinkled was recessive


What is Mendel's first law?

Principle of segregation
- Two alleles of a gene segregate from each other during gamete formation
- Had the gametes carry one allele and the other half carry the other


What is Mendel's second law?

The principle of independent assortment
- Genes controlling different characteristics assort into gametes independently to each other


Outline Mendel's second experiment

He asked if two different factors inherit differently
- He tested wrinkled/smooth peas and also their colour - yellow/green
- He asked if R/r Y/y move into gametes together or are there the combinations that are combined randomly
- He found 4 phenotypic classes in equal proportions - random


What did Mendel miss?

- Many genes have may alleles - not just two
- Not all alleles exhibit complete dominance or recessive
- Many genes fail to exhibit independent assortment - when lie on the same chromosome


What is incomplete dominance?

Phenotypes is intermediate between 2 parental phenotypes
eg. white and red carnation ---> pink flowered offspring


What is co dominance?

Simultaneous expression of two phenotypes
e.g. blood groups - A and B antigens are present on AB blood type


Outline Morgans genetic linkage ad recombination experiment in drosophila

- He crossed grey bodies drosophila with normal wings with a black bodies with vegetal wing
- F1 phenotype: grey with normal wings ---> dominant phenotypes
- He back crossed the F1 progeny with parental black/vegistal
- All 4 possible phenotypes shown but in unequal proportions
- He concluded that the backcross led to a majority of parental phenotype combinations because the genes were located on the same chromosome


How are non - parental combinations in Morgans experiment explained?

Explained by genetic crossovers in the formation of some gametes - genetic recombination
- Number of recombination Is proportional to physical distance between linked genes - allows gene mapping


How can genes be found to analyse?

- Human genetics - natural variation
- Induced mutations - chemicals or radiation that alter DNA sequences randomly
- Engineered changes - Removing gene sequences (targeted mutations) adding new gene sequences (transgene)


How can you find genes require for a particular biological process?

Genetic screen
- Identifies mutations that change gene function
- Usually inactivates mutations leading to a recessive phenotype


How do you design a genetic screen?

- Choose an organism that can be grown easily and observed
- Short generation time
- Can be mutanised easily using chemicals or x rays


How do we know when mutations causing similar phenotypes lie in the same or different genes?

- Genetic complementation test
- Cross mutants and see of any offspring are wild type. If yes the different genes