3.4.2 DNA and protein synthesis Flashcards
What is the genome?
the complete set of genes in a cell
What is a proteome?
the full range of proteins that a cell is able to produce
DNA - RNA - PROTEIN what processes occur in the central dogma
- transcription
2. translation Trna
What is mRNA involved in? Where does it occur and why ?
transcription in the nucleus as DNA cannot leave
proteins synthesized in cytoplasm on ribosomes
Why must an RNA copy of DNA be made?
so the genetic code can leave the nucleus
What is mRNA?
a single strand copy of genes DNA sequence
acts as messenger between nucleus and cytoplasm
transcript
How is mRNA synthesised?
- from template strand of DNA
template strand determines the sequence of bases on the mRNA
What is a sequence of 3 bases called and what do they do?
- triplets/codon
- an amino acid
What is tRNA involved in?
Where is it found
- translation which takes place on ribosomes
- cytoplasm and ribosomes (throughout cell)
What does tRNA do?
transfers free amino acid in the cytoplasm to the ribosome
Label tRNA parts?
- 3’ 5’ end amino acid attachment site (ATP needed)
- anticodon which is complementary to mRNA
- Nucleotides
- Hydrogen bonds due to complementary base pairs
What is the structure of tRNA?
single folded polypeptide chain with a clover shape
Where do amino acids attach to on the tRNA?
they attach to the amino acid attachment site on the 3’ 5’ end
What is the anticodon?
- sequence of 3 bases which is complementary to codon on mRNA molecule
if mRNA codon is AUG what is tRNA’s?
UAC
if mRNA codon is GAC what is tRNA’s?
CUG
Do tRNA molecules work for all amino acids?
No there are many different tRNA molecules with specific anticodons therefore each tRNA molecule is specific for only one amino acid
Compare DNA, mRNA and tRNA structure.
Polynucleotide strands 2, 1, 1
Shape double helix, straight single strand, clover shape
Compare DNA, mRNA and tRNA sugar and bases.
deoxyribose, ribose, ribose
ATGC, AUGC, AUGC
What is the most stable out of mRNA, tRNA and DNA and why?
1st DNA as H bonding holds 2 antiparallel strands
2nd TRNA has some H bonding
3rd MRNA no H bonding
What is the location of DNA, tRNA and mRNA?
- nucleus
- nucleus, cytoplasm and ribosome
- cytoplasm and ribosome
The genetic code is? (5)
NURDS
- Nonoverlapping
- Universal
- Read in triplets
- Degenerate
- Stop codons
Why is the genetic code non-overlapping?
each base is only read once during transcription this means each base is only part of 1 codon only
Would the same bases code for the same amino acids in all species?
yes as genetic code is universal
What is it meant by the genetic code is read in triplets?
each amino acid is coded for by an mRNA codon which is coded by a sequence of 3 bases
Why is the genetic code degenerate?
a specific amino acid can be coded for by more than one codon
What is a stopcodon?
they don’t code for amino acids but mark then end of the code of a polypeptide chain
Importance of a startcodon?
synthesis of a polypeptide chain will not begin until the ribosomes has read a start codon which is always AUG
What is noncoding parts of gene’s DNA called?
introns these are spliced out
leaving only coding
What is coding part of gene’s DNA called?
exons
What determines amino acid?
mRNA codons not tRNA
What is the purpose of eukaryotic transcription?
production of mRNA from DNA
Production of mRNA transcript from DNA template in nucleus
Once mRNA transcript made this can travel out of nucleus to be translated into a protein at the ribosome
Stages of eukaryotic transcription?
IETS
- Initation
- Elongation
- Termination
- Splicing
Stage 1 of eukaryotic transcription?
Initiation- transcription factors move from cyto to DNA in nuc
- they bind to specific sequence of bases called promoter region
- this allows enzymes RNA polymerase and DNA helicase to bind to the promoter region
Stage 2 of eukaryotic transcription?
Elongation- DNA helicase unwinds double stranded DNA exposing template strand
- Free rna nucleotides in nucleus complementary base pair with DNA template strand
- RNA polymerase joins adjacent rna nucleotides together in 5’-3’ direction by forming phosphodiester bonds ( CR uses ATP)
- PRE-MRA strand made
- DNA strands reform and rewind back into a double helix, h bond reform
Stage 3 of eukaryotic transcription?
Termination- when RNA polymerase reaches termination sequence the enzymes detach and the pre-mRNA molecules are released
this contains introns and exons
Stage 4 of eukaryotic transcription?
Splicing- a protein called spliceosomes splices introns out of the pre- mRNA
- exons joined by enzymes to form mature MRNA taht can leave the nucleus via nuclear pores and travel out of the cytoplasm
Similarities in prokaryotic and eukaryotic transcription?
- both mRNA strands are synthesised in 5’ to 3’
- both use DNA helicase and RNA polymerase
Differences in prokaryotic and eukaryotic transcription?
- P occurs in cytoplasm E in nucleus
- P no processing, no introns, no splicing
E processing, introns and splicing - P translation can occur whilst mRNA transcript is being made (simultaneous)
E these 2 processes are distinct one has to be complete before other one starts
Purpose of translation?
- production of a polypeptide chain from a sequence of codons on an mRNA strand (at ribosomes)
What are the first 3 steps of translation?
- mRNA associates with the ribosomes and ribosome moves to find the start codon
- tRNA molecules bring the specific amino acids needed to the ribosome
- the anticodons on tRNA molecules are complementary to mRNA codons. ribosome moves along mRNA bringing in 2 tRNA molecules at a time
What are the last 3 steps of translation?
- peptide bond is formed between AA via CR. bonds between tRNA and amino acid hydrolysed and tRNA leaves to pick up another specific amino acid
- ribosomes move along mRNA by 1 codon and new tRNA molecules arrive with complementary anticodons
- this is repeated until the ribsome reads a noncoding stop codon and ribosome detaches from the polypeptide chain
Where does translation occur in both eukaryotes and prokaryotes?
At ribosomes in cytoplasm
What determines how the folded protein structure of protein will be?
Position of R groups in polypeptide chain
Transcription Makes _______ Products in Eukaryotes and Prokaryotes
Different
Why does pre-mRNA contain introns and exons?
Introns and exons are both copied into mRNA during transcription
Where does splicing occur?
Nucleus
Explain why the percentage of bases from the middle part of the chromosome and end part are different (2)
Different genes
Have different base sequences
Codes for different proteins
Different sequences of bases code for different proteins. Explain how. (2)
Protein made up of (chain of) amino acids
Each amino acid has its own base code
Explain how copying bases more than once may give rise to differences in the protein (2)
Changes base sequence of later triplets/amino acid codes
How many tRNA molecules does the ribosome bring together at once?
2
What happens as the third amino acid is attached to the sequence?
The first tRNA is released and it is free to collect another amino acid
How is a protein produced from a polypeptide chain?
Polypeptide is folded to form the secondary structure
Secondary structure is folded to to produce the tertiary structure
Polypeptide chains are joined together to form a quaternary structure
What is the role of ATP during translation?
Required to provide energy to attach amino acids to tRNA
To form peptide bonds between amino acids
What is the role of the ribosomes?
the ribosomes move along the mRNA by 1 codon and bring in 2 tRNA molecules at a time
