4: Genetic information, variation and relationships between organisms Flashcards
What does DNA consist of?
- Deoxyribose (pentose sugar)
- Phosphate group
- An organic base (Adenine, Guanine, Cytosine, Thymine)
What does RNA consist of?
- Ribose (pentose sugar)
- Phosphate group
- An organic base (Adenine, Guanine, Cytosine, Uracil)
Give differences between RNA and DNA.
- DNA has Thymine, RNA has Uracil
* DNA is a double-helix with 2 polynucleotides joined by H-bonds; RNA is a short polynucleotide chain.
What is a codon?
A triplet of bases that code for a particular AA. These appear in RNA.
What is an intron?
A non-coding section of DNA.
What is an exon?
A coding section of DNA.
What is a gene?
A base sequence coding for a polypeptide’s AA sequence and functional RNA.
What is a locus?
The specific location of a gene on a chromosome.
How many different possible AAs and triplets can be formed?
20 AAs and 64 triplets.
What are features of the triplet code?
- Non-overlapping; each triplet is only read once and triplets don’t share base (so you read AGTCGATGA as AGT-CGA-TGA, not AGT-GTC-CGA-GAT-TGA)
- Degenerate; more than 1 triplet can code for the same AA.
- Universal; AAs coded for by sequences in humans is the same as AAs coded in other organisms and vice versa.
- There are start and stop codons.
What’s the difference between DNA in prokaryotes and eukaryotes?
- Eukaryotes; DNA is found in the nucleus and is linear. They’re associated with proteins called histones to form chromosomes (which are histones with DNA tightly wrapped around).
- Prokaryotes; DNA is short & circular, and not associated with proteins - therefore no chromosomes.
Define the term ‘allele’.
An alternative form of a gene. Each gene consists of 2 or more alleles (1 from each parent).
Define the term ‘homologous pair’.
2 chromosomes (1 from each parent) carrying the same genes (but they can carry different alleles of the same gene).
