4.1 - DNA, genes and chromosones

What are the three components of nucleotides?

1. pentose sugar
2. phosphate group
3. nitrogenous base

Describe the structure of DNA

Made up of a deoxyribose sugar, a phosphate group, and contains A,C,G,T organic bases. It is double stranded and hydrogen bonds between the bases to form a helix shape

Describe the role of DNA

Carries genetic information, determines our inherited characteristics

Describe the structure of RNA

Made up of a ribose sugar, a phosphate group, and one of four organic bases (A,C,G,U). It is single stranded

Describe the role of RNA

Transfers genetic information from DNA to ribosomes for protein synthesis

Which bases are purine and which are pyrimidine?

Purine (double ring) = adenine, guanine

Pyrimidine (single ring) = cytosine, thymine, uracil

How is DNA in eukaryotic cells different from in prokaryotic cells?

• Eukaryotic cells = found in nucleus, long and linear. Associated with histone proteins to form chromosomes. Mitochondria and chloroplasts contain prokaryotic-like DNA
• Prokaryotic cells = short and circular. Not associated with proteins

What is the genetic code?

The order of bases on DNA. Consists of codons (triplets of bases that code for a particular amino acid)

Identify features of the genetic code

• non-overlapping = each triplet is only read once
• degenerate = more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids)
• universal = same bases and sequences used by all species

What is a gene?

A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide. Can also code for functional RNA

What is a locus?

The fixed position on a DNA molecule occupied by a gene

What is an allele?

Different versions of the same gene, found at the same locus on a chromosome

What are exons and introns?

Exons = regions of DNA that code for amino acid sequences. Seperated by one or more introns

Introns = regions of DNA that do not code for anything

Where are introns found?

• between exons
• In DNA and pre mRNA