Molecular Genetics Flashcards
(27 cards)
What is the relationship between chromosomes and DNA?
DNA coils around proteins called histones to form nucleosomes, which further folds to form a long and thread-like fiber called chromatin, which undergoes duplication and condensation during cell cycle to form chromosomes.
What are nucleic acids?
They are a class of macromolecules found in all cells and viruses, which function in the storage (DNA) and expression (RNA) of genetic information. Each nucleic acid molecule is a polynucleotide made up by sub-united called nucleotides.
What are nucleotides made up of? Which nitrogenous base and sugars does DNA and RNA contain?
It is made up of a nitrogenous base (cytosine, guanine, adenine, thymine or uracil), a pentose (5 carbon) sugar (either ribose or deoxyribose) and a phosphate group.
DNA nucleotide-> Deoxyribose sugar and AGCT base
RNA nucleotide-> Ribose sugar and AGCU base
What is the structure of nucleic acids?
Nucleotides linked by phosphodiester bonds to form polymers called polynucleotides. Alternating sugars and phsophate groups form the sugar phosphate backbone that provides structural support to the molecule. The backbone is negatively charged and a nitrogenous base is attached to each sugar along the backbone.
What is the structure of DNA?
DNA is composed of 2 polynucleotide chains that coil around each other to form a double helix, like a rope ladder twisted into a spiral. Ropes at the side represents sugar-phosphate backbones while each step represents a pair of bases or base-pair. DNA bases pair complementarily, with A pairing with T and C pairing with G. These are joined by hydrogen bonds that helps to stabilise double helix.
What is the process of DNA replication?
- Both strands of a DNA molecule separate
- Both strands acts as a template that determines the order of nucleotides along a new complementary strand.
- New nucleotides complementary base-pair with nucleotides on template strand and are held in place by hydrogen bonding.
- DNA polymerase catalyses formation of phosphodiester bond between adjacent nucleotides to connect them into a strand.
- Each daughter DNA molecule consists of one parental strand and one new strand.
How does DNA specify the synthesis of proteins?
It will first undergo transcription and transfer genetic information from DNA into an RNA molecule in the nucleus.
Then, it will undergo translation and transfer information from the RNA molecule into polypeptides which then fold into proteins.
What is the process of transcription?
- Enzyme RNA polymerase attaches to DNA and starts to unwind and separate the DNA double helix.
- One DNA strand acts as the template.
- RNA nucleotides base-pair one by one with DNA bases on the template DNA strand via complementary base pairing. (A in DNA base pairs with U in RNA)
- RNA polymerase connects RNA nucleotides into a polynucleotide chain by catalysing the formation of phosphodiester bonds between RNA nucleotides.
- As RNA polymerase moves along DNA, it unwinds and exposes more of the template DNA strand for base-pairing with RNA nucleotides.
What is translation? Who are the key players?
It is the conversion from nucleic acid language to the protein language and occurs in the cytoplasm, based on the genetic code which is almost universal.
The key players are the messenger RNA, the transfer RNA and the ribosomal RNA with ribosomes.
What is the genetic code? What is the flow of info from gene to protein based on and what is that? How many codons are there?
It is the set of rules that convert a nucleotide sequence in RNA to an amino acid sequence.
The flow of information from gene to protein is based on a triplet code, called a codon. Codon is a triplet of bases, which codes for one amino acid.
There are 64 codons: 61 codes for amino acids (including one start codon that signals translation to start and codes for the amino acid, methionine) and 3 of them are stop codons instructing ribosomes to end the polypeptide (do not code for any amino acids)
What does the messenger RNA do? What does transfer RNA do? What does ribosomal RNA? What does ribosomes do?
It is produced by transcription in nucleus and transported to cytoplasm for translation and also contains the triplet codons.
It matches amino acids to the correct codons to form a polypeptide by recognising the matching correct codons in the mRNA and attaching to the specific amino acid.
It is associated with ribosomal proteins to form ribosomes, the machinery for translation and protein synthesis.
Ribosomes coordinate binding of tRNA to mRNA and catalyses the formation of peptide bonds between amino acids to form polypeptides. It is made up of 2 subunits: smaller unit binds mRNA and larger unit has 2 tRNA sites.
What is genetic engineering and how does it work?
Genetic engineering involves the transfer of genetic material from one cell to another and produces genetically modified organisms.
Genetic enginnering works by introducing a gene of interest into a host cell. Host cells carrying the human gene will then multiply in number and transcribes and translates the human gene into a protein.
What is recombinant DNA technology?
It is a set of techniques for combining genes from different sources into a single DNA molecule. This involves joining a target gene with a circular piece of bacterial DNA called a plasmid, which is introduced into a host bacterium that multiples very fast to make many copies of the DNA.
Why are bacteria used as host cells to clone DNA?
Bacteria have very short doubling time or high rates of reproduction. Growing recombinant bacteria results in very high numbers of bacteria with the target gene in a very short period of time.
What is bacterial plasmid? What are their characteristics?
They are circular, double-stranded DNA molecules.
They are separate from the bacterial chromosome and is easily exchanged between bacteria. They also are not essential for survival of bacteria but often give a survival advantage.
Why do scientists join target DNA to bacterial plasmid instead of bacterial chromosome?
Plasmids can easily incorporate foreign DNA and is readily taken up by bacteria. Plasmid also often contains gene coding for antibiotic resistance and it is easy to identify bacteria that had taken up the recombinant plasmid from those that didn’t. It also can self-replicate and is present in one or more copies in one bacterium.
Why do recombinant plasmids increase the yield of target DNA for use?
Recombinant plasmid self-replicates to produce multiple copies in each bacterium. When the bacterium divides, recombinant plasmid is also replicated and passed on to its descendants. Both rapid reproduction of bacteria and self-replication of recombinant plasmid produces large numbers of copies of the target DNA.
What are the major steps involved in DNA cloning?
Digestion, ligation, transformation and selection
What is required to produce recombinant DNA? How is recombinant DNA produced?
Bacterial plasmid and gene of interest
Cut out the target gene from the source and the circular plasmid to create a point of insertion using restriction enzymes. Splice and join the cut out target gene to the plasmid with the enzyme DNA ligase.
What are restriction enzymes? What is a palindromic sequence?
Restriction enzymes are found naturally in bacteria to digest foreign DNA. Each restriction enzyme only recognises a specific DNA sequence (restriction site) that is palindromic. Different enzymes recognise different restriction site sequences.
Nucleic acid sequences that are the same when read in opposite directions on 2 complementary DNA strands.
How do restriction enzymes operate?
What ends do restriction enzymes produce?
Restriction enzymes cut both strands of the DNA double helix at specific points in the restriction site by cleaving the sugar-phosphate backbone of DNA by catalysing the breaking of phosphodiester bonds.
They produce blunt ends (ends that are cut at the same position) or sticky ends (ends that are uneven)
How are sticky ends useful?
Plasmid and genes cut using the same restriction enzymes will produce the same sticky ends that are complementary.
The exposed nucleotides on sticky ends can undergo complementary base pairing by hydrogen bonding.
The cut plasmid and the gene will be held together by weak hydrogen bonds between complementary sticky ends to form recombinant plasmid.
How does DNA ligase work?
The sugar phosphate backbone is broken at the point of insertion, so the inserted gene is only held by weak hydrogen bonds at the sticky ends so it can detach easily.
DNA ligase is used to repair the sugar-phosphate backbone by catalysing the formation of phosphodiester bond to form an unbroken recombinant plasmid with an intact sugar phosphate backbone.
How to choose the restriction enzyme to use for DNA cloning?
Both plasmid and target DNA must be cut with the same restriction enzyme to produce complementary sticky ends. Hencem both must have the restriction site sequence of the chosen enzyme in their DNA sequence, except when using restriction enzymes that produce blunt ends.
The restriction site sequence of the chosen restriction enzyme must not be found within the target DNA’s sequence.
