Genes and Protein Synthesis Flashcards
(15 cards)
What is a gene?
A section of DNA bases that codes for one polypeptide.
What is an allele?
A different form of a gene.
What is the difference between DNA strands?
- Length.
- Sequence of bases.
What are three features of the triplet code?
1) The code is non-overlapping: each base is only part of one triplet.
2) The code is degenerate: more than one triplet can code for the same amino acid.
3) The code is universal: a given triplet specifies the same amino acid in all organisms.
What is rRNA?
Along with protein, makes up a ribosome.
What is mRNA?
- Formed by transcription of a gene in DNA in the nucleus.
- Complementary to the DNA.
- A single linear strand.
- Triplet of bases called a codon.
- mRNA has unpaired bases and so is easily broken in the cytoplasm.
What is tRNA?
- Transfer RNA is the shortest RNA molecule.
- It is a single strand which folds back on itself and hydrogen bonds with complementary sections to help stabilise the molecule.
- Clover-leaf shaped.
- Carry specific amino acids.
- Sequence of three bases, known as the anticodon.
What is an intron?
Non-coding DNA within a gene. Prokaryotes have no introns within their DNA whereas eukaryotes do have introns in their DNA (however mitochondria and chloroplasts contain DNA like that found in prokaryotes).
What is the genome?
The complete set of genes in a cell, including those in mitochondria and/or chloroplasts.
What is the proteome?
The full range of proteins that a cell is able to produce.
What is the process of transcription?
- The hydrogen bonds between DNA bases are broken which separates the two strands of DNA.
- One strand of DNA acts as the template strand upon which pre-mRNA is built.
- Free RNA nucleotides are found in the nucleoplasm. They are attracted to the exposed DNA bases on the DNA template strand and align by complementary base pairing.
- RNA polymerase join RNA nucleotides to make an RNA polynucleotide chain via phosphodiester bonds.
- Introns are removed and exons are spliced.
What is the process of splicing?
- DNA is made up of sections called exons that code for the amino acid sequence of polypeptides.
- Sections called introns do not code for amino acids sequences.
- Exons are sections of DNA that are expressed to produce proteins.
- In the pre-mRNA in eukaryotic cells, the introns are removed by enzymes before the mRNA moves into the cytoplasm.
- The remaining exons are then joined together. This is known as splicing.
- Following splicing, mRNA molecules leave the nucleus through the nuclear pores.
What is the process of translation?
- mRNA attaches to ribosomes.
- tRNA anticodons bind to mRNA codons by complementary base pairing.
- Each tRNA brings a specific amino acid.
- 2 tRNA molecules are held together in a ribosome at any one time.
- A peptide bonds forms between adjacent amino acids. This requires the use of ATP.
- tRNA molecules are released after their amino acids have been joined to the growing polypeptide chain.
- The ribosome moves along the mRNA forming the polypeptide until a stop codon is reached, at which point the ribosome and mRNA dissociate.
Compare DNA, mRNA and tRNA.
DNA:
- Double polynucleotide chain.
- Longest molecule of the three.
- Double helix shape.
- Pentose sugar is deoxyribose.
- Bases found are A, T, C and G.
- Found in mostly the nucleus.
- Chemically stable.
mRNA:
- Single polynucleotide chain.
- Shorter than DNA, longer than tRNA.
- Single linear strand (single helix).
- Pentose sugar is ribose.
- Bases found are A, U, C and G.
- Found in nucleus and cytoplasm.
- Less stable than DNA and tRNA and usually broken down within a few days.
tRNA:
- Single polynucleotide chain.
- Shortest molecule of the three.
- Single strand folded back on itself.
- Pentose sugar is ribose.
- Bases found are A, U, C and G.
- Manufactured in the nucleus but found throughout the cell.
- More stable than mRNA but less stable than DNA.
What is the advantage of mRNA being broken down relatively quickly?
- mRNA is used in protein production.
- A protein only needs to be produced when it is needed.
- mRNA breaks down once used and is made again when protein production is required.
