4.1 DNA, RNA and protein synthesis Flashcards
what is a gene?
a section of DNA on a chromosome that codes for one or more polypeptides
what is a locus?
the position of a gene on a chromosome
what is an allele?
different versions of the same gene
what is a genome?
all the genetic material inside a cel
what is an intron?
a section of DNA within a gene that doesn’t code for anything
what is an exon?
a section of DNA within a gene that codes for amino acids
what are homologous chromosomes?
a pair of chromosomes (one maternal, one paternal) that contain the same genes but potentially different alleles.
what is a triplet?
a series of three bases that code for an amino acid in a protein
what is a proteome?
the full range of proteins that a cell or organism can produce
what does it mean for the genetic code to be non-overlapping?
each base is only read once
what does it mean for the genetic code to be degenerate?
more than one triplet can code for the same amino acid
what does it mean for the genetic code to be universal?
each triplet codes for the same amino acid in all organisms
what organic bases are present in DNA?
adenine, thymine, guanine, cytosine
describe the structure of prokaryotic DNA [3]
short, circular, not associated with proteins
describe the structure of eukaryotic DNA [3]
long, linear, associated with histone proteins to form chromosomes
describe the structure of mitochondrial and chloroplast DNA [3]
short, circular, not associated with proteins
how is eukaryotic DNA compact?
DNA is wound around histone proteins then coiled up tightly to make a chromosome
how is prokaryotic DNA compact?
circular DNA is supercoiled
what is a codon?
a triplet/three adjacent nucleotides in DNA or mRNA that codes for an amino acid
what is functional RNA?
RNA molecules other than mRNA that perform special tasks during protein synthesis
when are chromosomes visible?
when a cell is dividing
where does transcription take place in eukaryotic cells?
the nucleus
where does transcription take place in prokaryotic cells?
the cytoplasm
what does RNA stand for?
Ribonucleic acid
describe the structure of RNA [3]
- polymer made up of mononucleotide sub-units
- nucleotides are made up of a ribose sugar, phosphate group and organic base
- single strand
what organic bases are present in RNA?
adenine, uracil, guanine, cytosine
what are the two types of RNA used in protein synthesis?
mRNA (messenger RNA)
tRNA (transfer RNA)
describe the structure of mRNA
a single-stranded polynucleotide chain arranged in a single helix that carries information in the form of codons
when is mRNA made?
during transcription
what is the function of mRNA?
to carry the genetic code from DNA in the nucleus to ribosomes in the cytoplasm, where it is used as a template for protein synthesis during translation
how is the structure of mRNA suited to its function?
it carries information in the form of codons, which determine the amino acid sequence of a specific polypeptide
describe the structure of tRNA
- single-stranded polynucleotide chain folded into a clover shape
- one end of chain extends further than the other, making amino acid binding site
- anticodon loop is on opposite end, which has a sequence of three organic bases (the anticodon) specific to an amino acid
what is the function of tRNA?
pairing the tRNA anticodon with the three organic bases on a complimentary mRNA codon
how is the structure of tRNA suited to its function?
it has an amino acid binding site and anticodon made of three organic bases, allowing it to line up amino acids on the mRNA template during protein synthesis
what is transcription? [1]
the first stage of protein synthesis, in which an mRNA copy of a gene is made from DNA
what is the first stage of protein synthesis?
transcription
describe the process of transcription [5-6]
- RNA polymerase enzyme attaches to DNA double helix at the start of a gene
- RNA polymerase breaks hydrogen bonds between DNA strands, causing them to separate and expose nucleotide bases
- one strand is used as a template strand, to which free nucleotides pair with complimentary bases
- RNA polymerase moves along strand, joining nucleotides together to form pre-mRNA molecule
- once RNA polymerase has passed, DNA coils back to double helix
- when RNA polymerase reaches stop codon, it detaches and process is complete
what is splicing?
the removal of introns and joining of exons in pre-mRNA to produce mRNA
where does splicing occur?
the nucleus
does splicing take place in prokaryotic cells?
no, as there are no introns in prokaryotic DNA
what is the second stage of protein synthesis?
translation
where does translation take place?
cytoplasm
what is translation?
the second stage of protein synthesis, in which amino acids join to form a polypeptide chain by following codons carried by mRNA
describe the process of translation [5-6]
- ribosome attaches to start codon on mRNA
- tRNA carries amino acids to it
- anticodon on tRNA attaches to first codon on mRNA strand by complimentary base pairing
- second tRNA attaches to next codon in same way
- peptide bond forms between adjacent amino acids
- first tRNA moves away, leaving the amino acid behind
- third tRNA binds to next codon on mRNA strand and its amino acid binds to the others
- second tRNA moves away
- process repeats until stop codon is reached, at which point chain of amino acids (polypeptide) moves away from the ribosome, and translation is complete
