Molecular genetics Flashcards
Define DNA
DNA is the genetic material that organisms inherit from their parents, and carries genetic code (genes), used for synthesising specific polypeptides
Define a chromosome
A chromosome is a DNA molecule condensed during cell division
What does a nucleotide consist of
- Phosphate group
- Deoxyribose sugar
- Nitrogenous base
How is the sugar phosphate backbone of a DNA molecule formed
Sugar phosphate backbone is formed when the phosphate group of one nucleotide joins with the deoxyribose sugar of the next nucleotide
What is the shape of the phosphate group
Circular
What is the shape of the deoxyribose sugar
Pentagon
What are the rules for complementary base pairing
- Adenine forms double hydrogen bonds with thymine
- Cytosine forms triple hydrogen bonds with guanine
Describe the process of DNA replication
- DNA replicates following the process of semi-conservative replication
- Each polynucleotide strand of original DNA acts as a template for the synthesis of a new complementary polynucleotide strand
- Original double helix first separated by enzymes
- Nucleotides are bound to separated polynucleotide strands following rules of complementary base pairing with the aid of enzymes
- Results in the formation of 2 double-stranded DNA molecules
What are the nitrogenous bases
- Adenine
- Thymine
- Guanine
- Cytosine
Define a gene
A gene is a unit of inheritance with a specific sequence of nucleotides, as part of a DNA molecule that contains the information to make a polypeptide
How does genetic information flow
DNA > RNA > Protein
Define transcription
Transcription is when the message in the gene is copied into an mRNA in the nucleus
Describe how polypeptides are synthesised
- In nucleus, message in gene is copied into an mRNA through process of transcription
- mRNA travels to cytoplasm and attaches itself to a ribosome
- Ribosome moves along the mRNA and synthesises a polypeptide through process of translation
- Polypeptide is released when ribosome leaves the mRNA
Define translation
Translation is the synthesis of a polypeptide chain from mRNA
How many bases on the mRNA make up a codon
3
What happens when a change occurs to the nucleotide sequence
- Type of amino acids on the chain changes
- Structure of protein changes
- Protein loses its function
When is a polypeptide chain functional
When it folds into a specific 3D shape
How many amino acids does a codon code for
1
What determines the sequence of amino acids in a protein
Order of nucleotide bases
What are the similarities between DNA and mRNA
- Both have a sugar phosphate backbone
- Both have 3 common nitrogenous bases
What is the structure of DNA
- 2 strands
- Double helix structure
- Deoxyribonucleotide monomer
- Deoxyribose sugar as the pentose sugar
- Contains thymine
- Hydrogen bonds between bases
What is the structure of mRNA
- 1 strand
- Straight chain structure (Mostly)
- Ribonucleotide monomer
- Ribose sugar as pentose sugar
- Contains uracil
- No hydrogen bonds if it is a straight chain structure
Define down syndrome
Down syndrome is caused by the non-separation of chromosome 21 in meiosis during gamete formation, resulting in the zygote having an extra chromosome 21, so body cell ends up with 47 chromosomes instead of 46
Define mutation
Mutation is a spontaneous or induced change in the DNA sequence of genes, or a change in the number or structure of chromosomes
Define mutagens
Mutagens are physical or chemical agents that can cause alterations to DNA, resulting in changes in the sequence of DNA
What is genetic engineering
Genetic engineering is used to transfer genes from one organism to another by using a vector
Describe sickle cell anaemia
- Sickle cell anaemia caused by a gene mutation, resulting in a substitution of a single amino acid in the haemoglobin protein
- Sickle cell haemoglobin molecules aggregate into long rods that deform the cells into a sickle shape
What is a vector
A vector carries the genes to the intended cells
What are plasmids
Circular strands of DNA that replicate separately from bacterial DNA
Why are bacteria used to produce insulin
- Easy to transfer genes into bacteria
- Bacteria contain plasmids, in which insulin genes can be inserted easily
- Bacteria take a short time to replicate
What is a restriction enzyme
A restriction enzyme is an enzyme that cuts the 2 ends of a gene to produce ‘sticky ends’
Describe how a human insulin gene is inserted into bacterial DNA
- Cut the human insulin gene with a restriction enzyme, producing ‘sticky ends’
- Each ‘sticky end’ is a single strand sequence of DNA bases, which can pair with complimentary bases to form a double strand
- Obtain a plasmid from a bacterium and cut the plasmid open with the same restriction enzyme, producing ‘sticky ends’ complementary to ends of insulin gene
- Mix plasmid with DNA fragment containing insulin gene
- DNA fragment with insulin gene will bind to plasmid by complementary base pairing of the ‘sticky ends’
- Add DNA ligase to seal DNA fragment to plasmid, forming a recombinant plasmid
- Mix plasmid with bacterium
- Apply heat or electric shock to open cell membrane for plasmid to enter
- Transgenic bacterium will synthesise insulin together with other proteins from plasmid
- Insulin must be extracted and purified before use
