DNA, Chromosomes Flashcards
Define gene
Section of DNA that codes for one or more polypeptides and functional RNA
The genetic code is degenerate. Explain what this means
Some amino acids are coded for by more than one triplet
The genetic code is universal. Explain what this means
The sequences that code for specific amino acids are the same in all organisms
The genetic code is non-overlapping. Explain what this means
Each base is only read once
What is the difference between introns and exons?
Introns are non-coding sequences of DNA removed in splicing, whereas exons are the polypeptide coding sequences.
Define locus
The position of a gene
Describe where DNA is found in eukaryotes and prokaryotes
DNA is found in the nucleus in eukaryotes, whereas in prokaryotes DNA is found in the form of a plasmid or loose in the cytoplasm. DNA is not bound to proteins in prokaryotes, whereas in eukaryotes it is bound to proteins called histones.
What is difference between the genome and the proteome?
The genome is the complete genetic information of an organism while proteome is the complete set of proteins that COULD BE encoded by a particular genome.
What is an allele?
An allele is one of a number of alternative forms of a gene
What are homologous chromosomes?
A homologous pair is a pair of chromosomes, one paternal and one maternal, that contain the same gene loci but not necessarily the same alleles.
Describe the structure of mRNA
- mRNA is a single polynucleotide strand, with a single helix structure.
- Its nucleotides contains ribose, a phosphate and an organic base (A, C, G or U).
- These nucleotides are joined by phosphodiester bonds.
- There are no hydrogen bonds as there are no bases pairs.
Describe the structure of tRNA
- tRNA is a single polynucleotide which forms a “clover” shape.
- Its nucleotides contain ribose, a phosphate and an organic base (A, U, C or G).
- These nucleotides are bonded together with phosphodiester bonds.
- Hydrogen bonds form between complementary bases as base pairing is present in the molecule.
- tRNA contains an amino acid binding site, and an anticodon - a sequence of three bases which are complementary to a codon - an amino acid coding sequence. Each tRNA is specific to one amino acid
What is an anticodon?
A sequence of three bases found in tRNA which are complementary to a codon - an amino acid coding sequence.
Give two differences between the structure of mRNA and the structure of tRNA.
- mRNA longer OR Has more nucleotides than tRNA;
- mRNA is a straight molecule but tRNA is a folded molecule / clover-leaf shaped molecule;
- mRNA contains no paired bases / hydrogen bonds but tRNA has some paired bases / hydrogen bonds.
DNA is a polymer of nucleotides. Each nucleotide contains an organic base. Explain how the organic bases help to stabilise the structure of DNA.
- Hydrogen bonds between the base pairs holds two strands together
- Many hydrogen bonds provides strength
Compare and contrast the structure of mRNA and tRNA
- Both are single stranded,
- Both contain nucleotides comprising of ribose, a phosphate and one of the bases UCAG.
- mRNA is a single helix, whereas tRNA is clover shaped.
- tRNA contains hydrogen bonds (between paired bases) whereas mRNA does not.
- mRNA is less stable than tRNA.
- tRNA contains a codon and an amino acid binding site, mRNA does not.
Contrast the structures of DNA and mRNA molecules to give three differences.
- DNA double stranded/double helix and mRNA single-stranded;
- DNA (very) long and RNA short; Accept ‛RNA shorter’ or ‛DNA bigger/longer’
- Thymine/T in DNA and uracil/U in RNA;
- Deoxyribose in DNA and ribose in RNA; Ignore ref. to histones Ignore ref. to helix and straight chain alone
- DNA has base pairing and mRNA doesn’t/ DNA has hydrogen bonding and mRNA doesn’t;
- DNA has introns/non-coding sequences and mRNA doesn’t;
A piece of mRNA is 660 nucleotides long but the DNA coding strand from which it was transcribed is 870 nucleotides long. Explain this difference in the number of nucleotides.
introns present in DNA;
