AQA AS Biology 7401- 3.4- Topic 8 DNA, Gene and Protein Synthesis

what is a gene

what is a locus

what does the DNA base sequence code for

in trying to discover how DNA bases coded for amino acids, scientists suggested that there must be a minimum of three bases that coded for each amino acid. their reasoning was as follows: Only [blank_start]20[blank_end] different amino acids regularly occur in proteins Each amino acid must have its own code of bases on the DNA Only [blank_start]four[blank_end] different bases are present in DNA If each base coded for a different amino acid, only four different amino acids could be coded for Using a pair of bases [blank_start]16 (4^2) different codes[blank_end] are possible, which is [blank_start]still inadequate[blank_end] Three bases produce [blank_start]64 (4^3) different codes[blank_end], [blank_start]more than[blank_end] enough to satisfy the requirement of [blank_start]20 amino acids[blank_end]

what is a triplet

further experiments have revealed the following features of the gentic code:

even within genes, only certain sequences code for amino acids. these coding sequences are called [blank_start]exons[blank_end]. within the gene these [blank_start]exons[blank_end] are seperated by further non-coding sequences called [blank_start]introns[blank_end].

in [blank_start]prokaryotic[blank_end] cells, such as bacteria, the dna molecules are [blank_start]shorter[blank_end], form a [blank_start]circle[blank_end] and are [blank_start]not associated[blank_end] with protein molecules. [blank_start]Prokaryotic[blank_end] cells therefore [blank_start]do not[blank_end] have chromosomes.

in [blank_start]Eukaryotic[blank_end] cells, the DNA molecules are [blank_start]longer[blank_end], form a [blank_start]line rather than a circle[blank_end] and occur [blank_start]in association[blank_end] with proteins called [blank_start]histones[blank_end] to form structures called [blank_start]chromosomes[blank_end]. the mitochondria and chloroplasts of [blank_start]Eukaryotic[blank_end] cells also contain DNA which, like the DNA of [blank_start]Prokaryotic[blank_end] cells, is [blank_start]short, circular[blank_end] and no associated with proteins.

chromosomes are visible during the whole cell cycle

each thread on a chromosome is called a [blank_start]chromatid[blank_end]

the DNA in chromosomes is held together by [blank_start]histones[blank_end]

How is DNA packed into chromosomes

[blank_start]sexually[blank_end] produced [blank_start]organisms[blank_end], such as [blank_start]humans[blank_end], are the result of the [blank_start]fusion[blank_end] of a [blank_start]sperm[blank_end] and an egg, each of which contributes [blank_start]one[blank_end] complete [blank_start]set[blank_end] of chromosomes to the offspring.

a homologous pair is always two chromosomes that carry the same genes but not necessarily the same alleles of the genes

what is an allele

if an allele is different, why is this?

where is eukarytoic DNA stored

the synthesis of proteins takes place in cytoplasm. how is it possible for the DNA to be transferred so it can be translated?

what are the two types of RNA? [blank_start]messenger[blank_end] RNA ([blank_start]m[blank_end]RNA) [blank_start]transfer[blank_end] RNA ([blank_start]t[blank_end]RNA)

the term [blank_start]codon[blank_end] refers to the [blank_start]sequence[blank_end] of [blank_start]three[blank_end] bases on [blank_start]mRNA[blank_end] that codes for a single amino acid

[blank_start]genome[blank_end]- the [blank_start]complete[blank_end] set of [blank_start]genes[blank_end] in a cell, including those in mitochondria and/or chloroplasts

[blank_start]proteome[blank_end]- the [blank_start]full[blank_end] range of proteins produced by the genome. this is sometimes called the complete proteome, in which case the term proteome refers to the [blank_start]proteins[blank_end] produced by a given type of cell under a certain set of conditions

RNA is made up of repeating mono nucleotide sub-units. it forms a single strand in which each nucleotide is made up of: