Bk 1 Ch5 Genes and genomes Flashcards
Gene
Region of DNA that specifies the amino acid sequence of a polypeptide or in some cases of functional RNA molecule
Origin of replication
A single point, Particula sequence of bases at which replication begins
DNA polymerases
Enzymes Enzymes that catalyse the assembly of deoxyribonucleoside triphosphates (dNTPs) into DNA during DNA replication. An existing DNA strand is required as a template.
Helicases
Enzymes which separates the base pairs and unwind to DNA strands
Single strand DNA binding (SSB) proteins
Prevent exposed stretches of single-stranded DNA from Reannealing to form the duplex
DNA topoisomerase
Enzyme that is part of the DNA relpication complex; introduces a temporary break in one of the strands of DNA, allowing the DNA helix to swivel around itself and reduce torsional stress during unwinding of the helix. The topoisomerase then reseals it.
Nuclease
Enzymes that break the links between the nucleotides in DNA.
Leading strand
The DNA strand that is copied continuously during DNA replication.
Lagging strand
The DNA strand that is copied discontinuously, as Okazaki fragments, during DNA replication.
Replication fork
The arrangement of DNA at the point where the two strands are being separated and replicated. Two replication forks are formed at an origin of replication, and proceed in opposite directions along the DNA.
Okazaki fragments
The short sections of DNA synthesised during the replication of the lagging strand of DNA.
DNA ligase
Enzyme whose function in the cell is to join DNA fragments produced during DNA replication (or repair). DNA ligase joins any DNA molecules that have complementary ends, and so is used in vitro during gene cloning to join DNA fragments produced by restriction endonucleases.
Mismatch repair(MMR)
A DNA repair system that detects and replaces wrongly inserted nucleotide in a newly synthesised DNA chain.
Base excision repair(BER)
A process that removes single damaged bases from DNA, and restores the correct nucleotide.
Open reading frame (ORF)
A continuous section of DNA sequence that encodes a polypeptide, or part of a polypeptide.
A series of triplet codons, uninterrupted by a stop codon
Mutation
Permanent change in DNA sequence
Pyrimidine
C ,T,U
Purine
A,G
Transition
One pyrimidine replaces the other
One purine replaces the other
Transversion
One purine replaces pyrimidine
Or vice a versa
Missense mutation
Substitution of one amino acid for another
Nonsense mutation
Premature stop codon
Operon
A group of bacterial genes, usually encoding proteins with related metabolic functions, that are under the control of a single regulatory DNA region (promoter), and which are transcribed as a single polycistronic messenger RNA. The first example described was the lac operon of E.coli.
Polycistronic transcript
A single mRNA molecule that is the product of the transcription of several genes arranged in tandem, typically the mRNA transcribed from an operon. The translation products are separate polypeptides.
Plasmids
Small autonomously replicating circle of DNA found naturally in many bacteria; some encode functions enabling their own transfer from cell to cell.
Restriction endonucleases
Enzymes present in many bacteria that recognise particular sequences in DNA and cut the nucleic acid within that sequence (or sometimes a fixed distance from it). The resulting double strand cuts usually have protruding single-stranded or ‘sticky’ termini which can be rejoined using the enzyme DNA ligase. Restriction endonucleases are widely used in gene cloning.
Cloning vectors
Self-replicating DNA molecules used to transfer DNA into cells. Most cloning vectors for use in bacteria are produced from naturally occurring bacteriophages or plasmids, which are engineered to introduce properties that facilitate gene cloning (e.g. restriction enzyme sites, selectable markers).
Horizontal gene transfer
The transfer of DNA from one organism to another organism that is not its offspring. The DNA transfer may be between different species.
Transformation
Genetic alteration of a bacterial cell by the uptake and incorporation of ‘naked’ DNA from the environment. Transformation occurs naturally in some species of bacteria and can be induced artificially in other cells. Because transformation has an alternative meaning in animal cells (indicating progression to a malignant, cancerous state) the term transfection is often used for this type of DNA uptake in animal cells.
Transduction
The transfer of DNA from one cell to another mediated by a virus.
Introns
Non-coding regions of a gene (located between exons) that are transcribed, but are spliced out of the primary transcript before the mature mRNA is used in protein translation. Common in eukaryotic genes but rare in prokaryotes.
Exons
Coding regions of a gene, i.e. parts of a gene that after transcription into RNA are spliced together by the removal of intervening introns (in eukaryotic cells) to be used as the template for protein synthesis.
mRNA splicing
The post-transcriptional process that removes non-coding sections (introns) from the primary RNA transcript in eukaryotic cells to produce the mature messenger RNA (mRNA) molecule.
Primary RNA transcript
A eukaryotic RNA transcript immediately after transcription in the nucleus, before any processing e.g. RNA splicing or polyadenylation.
TATA box
A consensus sequence present in the core promoter of most eukaryotic genes; the site where the transcription initiation complex (including general transcription factors and RNA polymerase II) assembles.
Transposons
A small genetic element that can move, or transpose, from one position to another in a genome; usually by copying itself and inserting into a second site, but sometimes by splicing out of the original site and inserting in a new location.
Satellite DNA
Heterochromatin
Contain few genes
Telomere
Regions at the ends of eukaryote chromosomes consisting of short non-coding nucleotide repeats. Their presence avoids the loss of coding regions during DNA replication (the 3’ end of the lagging strand cannot be replicated all the way to its end).
Telomerase
An enzyme that adds additional nucleotide repeats to the end of the chromosomes, thereby constantly restoring telomere length.
Active in germline cells and stem cells
And cancer cells
Single nucleotide polymorphisms (SNPs)
A type of genetic variation consisting of single nucleotide differences between the genomes of individuals.
Copy number variation (CNV)
A type of genetic variation where some genes may be present in a variable number of copies in different individuals of the same species, resulting in different levels of expression of the gene product.
Null mutation
Results in a complete loss of function of the mutated gene
Polymerase chain reaction (PCR)
A laboratory technique for amplifying a few copies of a DNA sequence to generate thousands or millions of copies by a series of in vitro reactions using DNA polymerase
1 denaturation (94*) - separate strands dna
2 primer annealing- base pairing oligonucleotide primers to complementary seq.
3elongation - synthesis 2 new dna strands by dna taq polymerase (not denatured), initiated from oligonucleotide primers
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