1.3- gene expression Flashcards
what is a genotype?
alleles an organism has for a particular characteristic
what is a phenotype?
appearance of an organism
what are genes?
DNA sequences that code for particular proteins
what are alleles?
different forms of a gene
what determines an organisms phenotype?
proteins produced as a result of gene expression
environmental factors also have influence
3 types of RNA involved in transcription and translation
messenger RNA
transfer RNA
ribosomal RNA
4 bases of RNA
adenine - uracil
cytosine - guanine
function of mRNA
carries a copy of the DNA code from the nucleus to the ribosome
function of tRNA
folds due to complementary base pairing
each tRNA molecule carries its specific amino acid to the ribosome
function of rRNA
rRNA and proteins form the ribosome
what is a codon?
group of 3 bases which codes for an amino acid
2 stages of protein synthesis
transcription
(RNA splicing)
translation
what happens during transcription?
mRNA carries a copy of the DNA code from the nucleus to the ribosome
4 steps of transcription
DNA double helix is unwound by RNA polymerase
hydrogen bonds between base pairs break, separating the two strands
as RNA polymerase breaks the bonds, it synthesises a primary mRNA transcript using RNA nucleotides which form hydrogen bonds with the exposed DNA strand by complementary base pairing
non-coding sections called introns are removed from primary mRNA transcript and coding sections called exons are joined together from the mature mRNA transcript by RNA splicing where the order of exons remains unchanged
8 steps of translation
the mRNA molecule travels through the cytoplasm and attaches to the ribosome
tRNA molecules transport specific amino acids to the ribosome
each mRNA codon codes for a specific amino acid
first codon of an mRNA molecule is a start codon which signals beginning of translation
anti-codons and codons match up and form complementary base pairs
peptide bonds join the amino acids together and form the polypeptide
used tRNA molecules exit the ribosome and collect another specific amino acid
last codon of an mRNA molecule is a stop codon which signals the end of translation
what is at the 3’ end of a tRNA molecule?
attachment site for a specific amino acid
what is at the opposite end of the 3’ of a tRNA molecule?
3 nucleotides with exposed bases
what are the exposed bases of a tRNA molecule called and what do they do?
anticodons
match up against the codons of the mRNA
what happens after translation?
polypeptide chains fold to form the three-dimensional shape of a protein held together by hydrogen bonds and other interactions between individual amino acids
5 types of proteins
structural proteins
receptors proteins
antibodies
hormones
enzymes
what is alternative RNA splicing?
when different proteins can be expressed from one gene
how are different mature mRNA transcripts produced?
depending on what exons are retained from the same primary transcript
