Human Cells: Gene Expression Flashcards
What is gene expression?
The process by which specific genes are activated to produce a required protein
What does gene expression involve?
The transcription and translation of DNA sequences
Genes are expressed to produce what?
Proteins
Only a fraction of the genes in a cell are what?
Expressed
Transcription and translation involves three types of RNA what are they?
mRNA, tRNA and rRNA
What is RNA?
It is single stranded and is composed of nucleotides containing ribose sugar, phosphate and one of four bases: Adenine, Cytosine, Guanine and Uracill
Messenger RNA (mRNA) does what?
Carries a copy of the DNA code from the nucleus to the ribosome
mRNA is transcribed from DNA where? And then translated where?
Transcribed from DNA in the nucleus.
Translated into proteins by ribosomes in the cytoplasm
What is the name and function of each triplet of bases on the mRNA molecule?
A codon.
It codes for a specific amino acid
Why does transfer RNA (tRNA) fold?
Due to complementary base pairing
What does a tRNA molecule have?
An anticodon (an exposed triplet of bases) at one end and an attachment site for a specific amino acid at the other end
What does each tRNA molecule carry?
Its specific amino acid to the ribosome
What forms the ribosome?
Ribosomal RNA (rRNA) and proteins
DNA is transcribed to produce what?
Messenger RNA (mRNA), which carries a copy of the genetic code
What happens in transcription?
The enzyme RNA polymerase moves along DNA unwinding the double helix and breaking the hydrogen bonds between the bases
RNA polymerase synthesises what?
A primary transcript of mRNA from RNA nucleotides by complementary base pairing
Uracil in RNA is complementary to what?
Adenine
Eukaryotic genes have what?
Introns and exons
The introns of the primary transcript are what?
Non-coding regions and are removed
The exons of the primary transcript are what?
Coding regions and are joined together to form the mature transcript
What happens to the order of exons during RNA splicing?
It is unchanged
RNA splicing forms what?
A mature mRNA transcript
What does the mature mRNA transcript do?
Carries a copy of the DNA code from the nucleus to the ribosomes, where it is translated
What is tRNA involved in?
The translation of mRNA into a polypeptide at a ribosome
Most codons code for specific amino acids but what other types of codons are there?
Start codons and stop codons
Where does translation begin and end?
It begins at a start codon and ends at a stop codon
Amino acids are carried by what?
Specific tRNA molecules
tRNA anticodons align and bond to mRNA codons by complementary base pairing, doing what?
Translating the genetic code into a sequence of amino acids
Peptide bonds join the amino acids together to form what?
A polypeptide
Following polypeptide formation, what happens to tRNA?
It exits the ribosome to collect further amino acids
Different proteins can be expressed from one gene, as a result of what?
Alternative RNA splicing
Different mature mRNA transcripts are produced from the same primary transcript depending on what?
Which exons are retained
Polypeptide chains fold to form what?
The three-dimensional shape of a protein, held together by hydrogen bonds and other molecular interactions between individual amino acids
Proteins have a large variety of shapes which determines what?
Their functions
Gene expression results in what?
Proteins which determine the phenotype of an individual organism
What also influences phenotype?
Environmental factors
