Unit 1.3 Gene expression Flashcards
What is RNA
A single stranded molecule, compromised of nucleotides
What do the nucleotides in RNA contain
ribose sugar, phosphate & base (cytosine, guanine, adenine & uracil)
What does gene expression involve
The transcription & translation of DNA sequences
How much of the genes in a cell are expressed
Only a fraction
The differences between DNA & RNA
DNA- 2 strands
RNA- 1 strand
DNA- adenine pairs with thymine
RNA- adenine pairs with uracil
DNA- nucleotide contains deoxyribose sugar
RNA- nucleotide contains ribose sugar
DNA- found in the nucleus
RNA- found in the nucleus & cytoplasm
3 types of RNA
messenger RNA
transfer RNA
ribosomal RNA
Function of mRNA
copies a section of the DNA code & carries it to the ribosome in the cytoplasm
Function of tRNA
carries specific amino acids into position at the ribosome
Function of rRNA
along with proteins make up the ribosome which is involved in protein synthesis
What is a triplet of bases on a mRNA molecule called
a codon
What does one codon code for
a specific amino acid
What causes tRNA to fold
Complementary base pairing
What type of codon do tRNA molecules contain
Anti-codon (an exposed triplet of bases)
What site is at the other end of a tRNA molecule, to help carry the specific amino acids to the ribosome
The attachment site
What does DNA carry the code for
Making proteins
What are the 3 stages of protein synthesis called
Transcription (of gene), RNA splicing, Translation
What happens in the transcription stage
The section of the DNA code required (gene) is copied into mRNA. This is known as the primary transcript.
What happens in the RNA splicing stage
The non-coding information (introns) in the primary transcript must be removed by splicing. The coding regions (exons) are joined together after the introns are removed, creating a mature mRNA strand.
What happens in the translation stage
The spliced mature mRNA strand is used to assemble amino acids in the correct order to make the protein
Where does transcription occur
The nucleus
Where does RNA splicing occur
The nucleus
Where does translation occur
The ribosome (in the cytoplasm)
Explain the steps in the process of transcription
1- RNA polymerase moves along the DNA, unwinding the double helix.
2- weak hydrogen bonds between bases break, so DNA strands separate
3- RNA polymerase adds free moving RNA nucleotides to the growing mRNA strand, by complementary base pairing
4- weak hydrogen bonds form between the new base pairs (of the DNA template & mRNA strand)
5- strong chemical bonds form between the new RNA nucleotides (opposite the DNA), allowing a new strand to be formed
6- weak hydrogen bonds break between DNA & RNA, allowing mRNA to break from the DNA template
7- a primary mRNA transcript is formed & ready to undergo splicing
8- weak hydrogen bonds reunite the 2 original DNA strands into a double helix again
What are long sections of DNA that do not code for a polypeptide called
Introns
Where are introns found
In between sections of DNA that do code for the proteins (polypeptides)
What are the coding regions on DNA called
Exons
What makes up the mature mRNA
Only exons (order is unchanged)
What happens once the mature mRNA is created
It leaves the nucleus & enters the cytoplasm for the next stage
What enzyme directs transcription
RNA polymerase
What is translation
The process which translates the code found on mRNA into a polypeptide
What molecule is involved in the translation of mRNA
tRNA
Describe the steps in process of translation
1- translation is initiated by the start codon (AUG) on the mRNA strand
2- tRNA molecules become attached to their specific amino acid molecules
3- these tRNA molecules then accumulate at the ribosome
4- the first tRNA molecule moves in & its anticodon forms a complementary base pair with the codon on the mRNA
5- another tRNA molecule carries an amino acid to the ribosome. more complementary base pairings occur, bringing the amino acids inline with each other. A peptide bond forms between the amino acids
6- the first tRNA molecule detaches from the mRNA & is free to collect another amino acid from the cytoplasm
7- this process is repeated all along the mRNA transcript until a stop codon is reached at the 3’ end & the newly formed polypeptide chain is complete
What is always the start codon
AUG
Function of a ribosome
Site of protein synthesis
What type of bond forms between amino acids & what does this create
Peptide bonds & a polypeptide
How can different proteins be expressed from one gene
As a result from alternative RNA splicing
How does alternative RNA splicing work
Different mature mRNA transcripts are produced from the same primary transcript depending on which exons are retained
What do polypeptide chains fold to form & what holds this together
A 3D shape of a protein, held together by hydrogen bonds & other interactions between amino acids
What is a phenotype
The physical appearance of an organism
What can determine the phenotype
The proteins produced from gene expression or environmental factors
What is a cells function determined by
The sequence of the DNA bases in its genes
What is a cells structure determined by
The proteins that are synthesised when the genes are expressed
What is gene expression influenced by
Environmental factors, inside & outside of the cell
