3. Gene Structure Expression and Regulation Flashcards
(37 cards)
What is a gene?
A segment of DNA that codes for proteins
What is the template strand?
Template strand of DNA contains the coded information of a particular gene, also called antisense or non coding strand.
What is the complementary strand?
The non template strand or the sense strand or the coding strand.
What is the coding region?
The coding region is the part of a gene that contains coded information for making a protein. In eukaryotic cells it is not continuous.
What are introns and exons?
Introns are non coding regions of DNA and exons are coding regions of DNA
What is the central dogma of molecular genetics?
The idea that DNA makes proteins by way of an intermediate RNA. Information can only flow from DNA to proteins
What is transcription?
It is the process of copying the genetic instructions present in the DNA to messenger RNA. Occurs in the nucleus of eukaryotic organisms and in the cytoplasm of prokaryotic organisms.
What are the steps in transcription?
- the enzyme RNA polymerase binds to a specific base sequence of the DNA template strand of the promoter region of a gene to be transcribed,
- the DNA unwinds and exposes the bases of the template strand,
- the base sequence of the DNA template strand (3’ to 5’) guides the formation of a complementary copy of mRNA. Free complementary RNA nucleotides pair with DNA and are joined together one by one to form a chain of mRNA or premrna in eukaryotes.
- the enzyme RNA polymerase catalysers this reaction adj copies the DNA until it reaches a stop signal, terminating RNA production
- a single stranded molecule of mRNA or premrna results adm is complementary to the base sequence of the DNA strand
- mRNA transcript or premrna is released and the double helix reforms.
What happens in pre-mRNA processing in eukaryotes?
- a methylated cap is added
- a poly a tail is added
- introns are spliced out
What is translation?
Translation is the process of decoding the genetic instructions where the order of bases in the mRNA transcript is used to produce a specific polypeptide amino acid chain.
Where does translation occur?
Occurs in the cytoplasm at the ribosomes of both eukaryotic and prokaryotic organisms
What is rRNA?
Produced in large quantities in the nucleus and stored there to form the nucleolus. rRNA moves from the nucleus to the cytoplasm when it is required to form part of ribosomes. Binds to proteins to make ribosomes.
What structures are required for translation?
- mRNA carries the code from the DNA and contains codons.
- tRNA is responsible for transporting amino acids to their correct position on the mRNA and contains anti codons.
- ribosomes: provides the environment for tRNA attachment and amino acid linkage
- pool of amino acids
What are the steps in translation?
- the mRNA carrying the code transcribed from DNA is transported from the nucleus through the nuclear pore to the ribosome in the cytoplasm.
- the small ribosomal subunit bonds to the methylated cap on the mRNA and scans along the mRNA for an Aug. Once found, a large ribosomal subunit joins with the small one commencing translation when a start codon is translated.
- a tRNA molecule with the complementary anti codon pairs momentarily with the mRNA releasing its amino acid.
- as the ribosome moves along the mRNA more amino acids are added to the growing polypeptide chain and peptide bonds between adjacent amino acids form, catalysed by enzymes in the ribosomes.
- when the ribosome reaches a stop codon protein synthesis stop and the polypeptide chain is released.
What does the order of nucleotides determine?
The order of nucleotides in DNA determines the order of nucleotides in mRNA which determines the tRNA that will bind to the mRNA which in turn determines the order of the amino acids linked together to produce a protein.
What does alternative splicing of pre mRNA do?
Results in amino acid sequence of polypeptide chain being different, proteins having different secondary and tertiary structures and different functions.
What are the differences between prokaryotic and eukaryotic DNA in terms of shape?
-in prokaryotes the main chromosome is a circular molecule of DNA and in eukaryotes it is a linear molecule of DNA
How does prokaryotic and eukaryote DNA differ in terms of histones?
Prokaryotic DNA is naked
Eukaryotic DNA exists in complexes with proteins called histones
How does P and e DNA differ in terms of nucleotide sequences?
Prokaryotic DNA comprises unique nucleotide sequences
Eukaryotic DNA comprises many repeated sequences
How does prokaryotic DNA differ from e in terms of where it is in the cell?
P DNA is free within the cell
E DNA is enclosed within the membrane of the nucleus
How does p and e DNA differ in terms of the coding sequences of genes?
P DNA has uninterrupted coding sequences of genes
In eukaryotic DNA exons are interrupted by introns
How does p and e DNA differ in terms of plasmids?
As well as main chromosome, additional DNA in the form of plasmids is present in prokaryotes.
In eukaryotes plasmids are absent
Processing of gene information in prokaryotic cells
- As there is no nuclear envelope, mRNA can associate with ribosomes as the mRNA is being formed
- mRNA is not interrupted because bacterial mRNA does not contain introns
- translation of mRNA into proteins begins before transcription is complete
- mRNA molecules often contain transcripts of several genes. By placing genes with related functions on the she, mRNA bacteria can synthesis these proteins in coordination
Processing of gene information between prokaryotic and eukaryotic cells
- because these cells possess a nucleus, the mRNA is formed completely and must cross the nuclear envelope before translation
- before translation the mRNA is modified by the removal of introns and addition of methylated cap and poly a 3’ tail.
- translation begins at the ribosomes in the cytoplasm
- mRNA usually specifies a single protein
- absence of operons
