1.3 Flashcards
What are genes ?
DNA sequences that code for particular proteins. Although every individual will have genes for the same proteins, there may be different forms the gene, these are called alleles.
What is a genotype?
The alleles an organism has for a
particular characteristic.
What is a phenotype?
The physical appearance of an organism.
How does RNA differ from DNA?
- RNA is single stranded whereas DNA is double stranded.
- RNA bases include cytosine, guanine, aenine and urcail, whereas DNA bases include cytosine, guanine, adenine and thymine.
- RNA contains a ribose sugar, whereas DNA contains a deoxyribose sugar.
What are the three types of RNA?
Messenger RNA (mRNA), Transfer RNA (tRNA) and Ribosomal RNA (rRNA).
What is messenger RNA (mRNA)?
carries a copy of the DNA code from the nucleus to the ribosome for translation
What is transfer RNA (tRNA)?
folds due to complementary base pairing. Each tRNA molecule carries its specific amino acid to the ribosome.
What is ribosomal RNA (rRNA)?
(and proteins) form the ribosome.
Where does transcription take place?
in the nucleus
What are the stages of transcription? (4 stages)
- mRNA carries a copy of the DNA code from the nucleus to the ribosome. It is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm.
- During transcription, the DNA double helix is unwound by RNA polymerase.
- Hydrogen bonds between base pairs break, separating the two strands.
- As the RNA polymerase breaks the bonds, it synthesises a primary transcript of mRNA on the DNA template using free RNA nucleotides.
Where does RNA splicing take place?
in the nucleus
What is RNA splicing?
This process removes the non-coding sections called introns from the primary mRNA transcript and joins together the coding sections called exons from the mature mRNA transcripts.
The order of the exons is unchanged during splicing.
Once the DNA of a gene has been transcribed into mRNA, the mRNA molecules pass through the nuclear pores into the cytoplasm. Here, translation of mRNA into polypeptides takes place in ribosomes.
What is translation? (6 stages)
- tRNA is involved in the translation of mRNA into a polypeptide at a ribosome.
- Each molecule of tRNA is a single-stranded folded shape, as a result of base pairing, using hydrogen bonds.
- At the 3’ end of the strand is the attachment site for a specific amino acid and at the opposite end of the molecule are three nucleotides with exposed bases. These exposed bases are called anticodons and match up against the codons of the mRNA.
- Translation begins at a start codon and ends at a stop codon.
- Anticodons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids.
- Peptide bonds joins the amino acids together. Each tRNA then leaves the ribosome as the polypeptide is formed.
What is a codon?
a RNA sequence of 3 nucleotides that encodes for a specific amino acid.
What is the role of a start codon?
a sequence of 3 nucleotides that is the first codon in an mRNA transcript that is translated by a ribosome and commences translation.
