Gene Structure and Expression (3.2) Flashcards
Define genes
Region of DNA that may be translated into a polypeptide or a functional RNA molecule
State how many nucleotides in length a gene can be
Millions of nucleotides in length
Describe the genetic code
Set of rules defining how information in nucleic acids is translated
Describe triplet
Sequence of three nucleotides in DNA that carries genetic information for an amino acid sequence
Describe codon
Sequence of three nucleotides on mRNA that codes for a particular amino acid (or indicates the beginning or end of translation)
State when a triplet is termed ‘codon’
DNA triplet is transcribed into mature mRNA
State what a triplet or codon codes for
Amino acid
State whether the genetic code is universal.
Genetic code is universal
Describe the degeneracy of the genetic code
More than one codon may code for a particular amino acid
Describe the process of calculating the total number of codon combination
4 nucleotides
3 nucleotides code for an amino acid
Therefore, 4^3 = 64
Describe the benefit of genetic code degeneracy
Buffer for gene mutation - a single change in one base may not necessary change the amino acid produced
State 4 structural features common in all eukaryotic genes
- Stop and start triplet sequences
- Promoter regions
- Exons
- Introns
Provide an alternative term for introns
Spacer DNA
State what the start triplet indicates
Gene expression will begin
Describe what the start triplet will become when it is transcribed into mRNA
Start codon
Describe what the start codon initiates
Translation
Provide one example of a start codon sequence and the amino acid it codes for
Methionine (AUG)
Describe what the stop triplet indicates
Transcription will end
State whether or not the stop triplet codes for an amino acid.
Stop triplet does not code for an aino acid
Describe what the stop triplet will become when they are transcribed into mRNA
Stop codons
State the 3 unique stop codons
UAA, UAG, UGA
Describe the promoter region
Sequence of DNA to which RNA polymerase binds
State the 4 major functions/characteristics of the promoter region
- location where the RNA polymerase attached to the gene
- identifies which DNA strand will be transcribed
- identifies where transcription of the gene will start
- identifies in which direction transcription will occur
State what the promoter region is coded for by in many eukaryotic genes
TATA box (sequence of bases TATAAA)
State whether all sections of a gene are translated within eukaryotes. True/false.
False
Describe exons
Regions of a gene that are usually ‘expressed’ as proteins or RNA
Describe what exons come together for
To make up mRNA
Describe introns
Non-coding regions of a gene
Describe the process of gene expression
Process by which the information stored in a gene is used to synthesis a functional gene product
Provide 2 examples of functional gene products
- proteins
2. RNA
Describe the regulation of the gene expression process
Highly regulated so that proteins or RNA molecules are only produced if and when they are required by a cell
Describe what the regulation of the gene expression process results in
Conservation of energy and materials in the cell
State the 3 stages of gene expression leading to protein synthesis in the correct order
- Transcription
- RNA processing
- Translation
Describe transcription
Production of single-stranded mRNA from DNA
State the location of transcription
Nucleus of eukaryotes
Describe the transcription unit
DNA segment that undergoes transcription
State the 3 steps of transcription
- Initiation
- Elongation
- Termination
Describe the initiation process of transcription
RNA polymerase binds to the promoter and separates the DNA strands
State what is required for RNA polymerase to attach to DNA in transcription
Transcription factors
Describe how RNA polymerase unzips DNA molecules
Breaking the weak hydrogen bonds between the two strands to expose the bases
Describe the elongation process of transcription
RNA polymerase ‘reads’ DNA template and builds an RNA molecule out of complementary nucleotides - chain grows 5’ to 3’
Describe what transcription factors combine with during the initiation process of transcription
Transcriptions factors combine with the promoter
Describe the approximate number of base pairs covered by an RNA polymerase molecule in transcription
30 base pairs
State approximately how many base pairs are uncoiled in one region of RNA polymerase cover
approx. 15/30 base pairs
State the direction of mRNA synthesis
5’ to 3’ direction
State which end of mRNA nucleotides are added to during transcription
3’ end
Describe what mRNA is termed after it has been transcribed
primary RNA transcript
State whether or not DNA strands located behind the transcription bubble recoil
Yes. DNA strands located behind the transcription bubble are coiled again
Describe what the primary RNA transcript is processed into during transcription
Mature mRNA
Describe the termination process of transcription
Terminators signal completion of RNA transcript. Transcript is released from the RNA polymerase.
State when transcription ends
RNA polymerase reaches the termination site of the gene
State what the termination site of a gene contains
Stop triplet code
Describe the function of the stop triplet code in transcription
Binds release factors that signal termination
State the term used to describe the strand of DNA that is transcribed to the mRNA
Template strand
State the term used to describe the complementary strand of DNA
Coding strand
Does mRNA carry the same base sequence as the coding strand?*
Yes. mRNA carries the same base sequence, however it contains uracil in place of thymine
Describe RNA processing
Primary RNA transcript undergoes processing before it is translated
Describe the 3 stages of RNA processing
- addition of 5’ cap
- addition of poly-A-tail
- splicing
Describe the 5’ cap
Cap added to the 5’ of the primary RNA transcript during RNA processing
Describe the structure of the 5’ cap
Consists of methylguanosine triphosphate
Describe the poly-A-tail
Chain is added to the 3’ end of the primary RNA transcript during RNA processing
Describe the structure of the poly-A-tail
Consists of up to 250 adenine nucleotides
Describe the benefit of the 5’ cap modification
Aids the binding of the ribosome to the mRNA at the beginning of translation
Describe the benefit of the poly-A-tail modification
Increase stability and prevent degradation
Describe splicing
Spliceosome removes the introns from the primary RNA transcript and joins the exon sections to make mature mRNA
Describe where the mature mRNA exits the nucleus
Via the nuclear pore
Describe splicing in prokaryotes
Most prokaryotes only contain exons and therefore splicing is not required
Describe the structure of mature mRNA composed during splicing
Single-stranded
Describe alternative splicing
Unique splicing can result in alternative mature mRNA strands from a single gene and thus different proteins
State the major function of alternative splicing
Reason why 21000 genes of humans can produce many more than 21000 proteins
Describe what introns were referred to as in early gene structure research
‘Junk DNA’
Describe translation
Codons on mRNA are translated into a sequence of amino acids which compose a polypeptide
Describe the 3 steps of translation
- Initiation
- Elongation
- Termination
Describe the initiation process of translation
Ribosome combines with mRNA and the first tRNA so translation can begin
Describe the elongation process of translation
Amino acids brought to the ribosome by tRNAs and link together to form a chain
Describe the termination process of translation
Finished polypeptide is released to function in the cell
Describe how protein synthesis begins
Ribosomal subunit attaches to the 5’ end of an mRNA strand
Describe the function of tRNA molecules in the initiation process of translation
tRNA carries anticodon to the mRNA codons, attaching the codon and anticodon by complementary base pairing
State what attaches to the tRNA and ribosomal subunit in the initiation process of translation
Large ribosomal subunit
State what the binding of the large ribosomal subunit results in
Formation of three binding sites for tRNA
State the 3 binding sites of tRNA
- aminoacyl site (A)
- peptidyl site (T)
- exit site (E)
Describe where that attachment of amino acids to their corresponding tRNA molecules occurs
Cytosol
State whether or not the initiation process of translation is catalysed by enzymes
Yes. The initiation process is catalysed by enzymes.
Describe the bond that forms between deposited amino acids
Peptide bonds
State whether or not the tRNA molecules of translation can be reused
Yes. tRNA molecules can be reused throughout translation
State what halts the attachment of amino acids during translation
Reaching of a stop codon
State what happens to the polypeptide chain when a stop codon is reached
Released from the ribosome into the cytoplasm or endoplasmic reticulum
Describe what happens to proteins of quaternary structure
Associate in the cytoplasm or the Golgi apparatus to form the fully functional protein
Describe the benefit of translating the same, single strand of mRNA at the same time
Enables many polypeptide chains to be produced simultaneously
State what happens to the polypeptide chains once they are fully functional
Remain in cell or are exported via exocytosis for use somewhere else within the organism
Describe the process of transcription and translation in prokaryotes
Continuous process, as all cellular processes occur within the cytosol
Describe whether or not splicing is required during transcription and translation in prokaryotes and suggest a reason why this might be
Prokaryotic DNA only contains exons, therefore splicing is not required
State how many protein synthetic initiation factors prokaryotes have
3 initiation factors
State how many protein synthetic initiation factors eukaryotes have
10 initiation factors
State whether or not a 5’ cap and poly-A-tail is added to prokaryotic mRNA
No 5’ cap or poly-A-tail is added to mRNA in prokaryotes
Describe when protein synthesis begins in prokaryotes
During transcription
Provide a term used to describe the beginning of protein synthesis during transcription in prokaryotes
Coupled transcription-translation
State why coupled transcription-translation can occur in prokaryotes
Ribosome and DNA are both found in the cytosol together
Describe when protein synthesis begins in eukaryotes
During translation
mRNA contains the coding sequence of ________ ________ in prokaryotes
Several genes
mRNA contains the coding sequence of ________ _________ in eukaryotes
One gene
State how many prokaryotic ribosomal subunits are involved in protein synthesis
30S-50S ribosomal subunits
State how many eukaryotic ribosomal subunits are involved in protein synthesis
40S-60S ribosomal subunits
State in what direction RNA polymerase runs along DNA template
3’-5’
State whether the methyl cap is added to the 3’ or 5’ end of the synthesised mRNA strand
3’ end
State whether the poly A tail is added to the 3’ or 5’ end of the synthesised mRNA strand
5’ end
State in what direction the mature mRNA strand enters the ribosome for translation
3’ end (methyl cap)
State why new nucleotides are added to the 3’ end of DNA backbone
OH allows for binding of nucleotide compared to phosphate which does not
