D1.2 Protein Synthesis Flashcards
Name 3 forms of RNA (3)
mRNA
rRNA
tRNA
Define mRNA (2)
messenger RNA made as a complementary strand to one DNA strand
copy of other DNA strand + contains uracil
Define rRNA (2)
ribosomal RNA found in ribosomes
decodes mRNA into amino acids
Define tRNA (2)
transfer RNA carries amino acids to ribosomes
bonded together to form polypeptides
Features of Transcription (4)
first step for cell to build protein
production of RNA (mRNA) using DNA as template
transcription takes place in nucleus in eukaryotic cells
transcription takes place cytoplasm for prokaryotes
Stages of transcription (3)
DNA strands separated into 2 stands + RNA polymerase binds to DNA strand
RNA polyemrase builds mRNA on one of strands (complementary to template strand/antisense strand)
terminator sequence (“stop” codon) in DNA reached + mRNA detached
Define the template strand/antisense strand for DNA (2)
strand with directionality 3’ to 5’
strand connected to mRNA
Define triplet for DNA
group of 3 bases for DNA
Define codons for DNA
group of 3 bases for mRNA (complementary to DNA triplet)
Features of translation (3)
only genes transcribed into mRNA are translated into proteins
mRNA moves out of nucleus via nuclear pore once transcribed
mRNA combines with ribosome in cytoplasm
Process of translation (5)
mRNA attaches to ribosome at start codon (AUG)
tRNA with complementary anticodon (UAC) attaches to mRNA
tRNA attached to amino acid (methionine)
ribosome moves along mRNA + brings 2 tRNA molecules at any one time
enzyme + ATP used to join amino acids with peptide bond
Why bases are complementary to each other
complementary bases form hydrogen bonds with each other but not with other bases
Directionality of transcription
3’ to 5’
Features of mRNA in translation (4)
has site for ribosome to bind to
has sequence of codons which codes for specific amino acids
has start + stop codon to indicate when translation will stop/start
mRNA can be translated multiple times but is broken down if it is damaged or if polypeptide it codes for is no longer needed
Features of tRNA (transfer RNA) in translation (4)
translates base sequence of mRNA in to amino acid sequence
tRNA has anticodon at one end + attachment point at other end for amino acid corresponding to anticodon
transfers corresponding amino acid to end of growing polypeptide once code on mRNA recognised
tRNA has specific corresponding amino acid attached
Shape of tRNA (3)
single-stranded RNA molecule
folds on itself to form clover-leaf structure
with double stranded regions + 3 hairpin loops
Features of ribosomes in translation (4)
acts as enzyme to form peptide bonds between amino acids
complex structure of small + large subunit
small subunit binds to mRNA
large subunit has 3 binding sites for tRNA
Define an anticodon
3-base code complementary to the matching RNA codon
Stages of translation (3)
initiation
elongation
termination
Elongation stage of translation (5)
ribosome moves along mRNA, one codon at a time
as each codon moves into place, new tRNA carries corresponding amino acid,
attaches + moves previous tRNA molecules to the next position
new amino acids are delivered = condensation reactions catalysed + peptide bonds formed
repeats until termination codon reached
Directionality of translation
5’ to 3’ direction
Define a promoter (3)
section of DNA that initiates gene transcription
proteins known as transcription factors bind to promotor-
act as binding point for RNA polymerase enzymes that catalyse transcription
Importance of transcription factors (2)
binding of correct transcription factors –> allows the RNA polymerase to also bind + begin to transcribe the DNA into RNA.
transcription factors are missing or cannot bind to the promoter = transcription will not take place and that gene cannot be expressed
Features of non-coding genome (3)
98% of the human genome
DNA sequences within genome that do not have information to make protein.
not represented within the amino acid sequence of expressed proteins.
Regions of non-coding DNA (4)
regulators of gene expression
introns
telomeres
genes for tRNA + rRNA
Define regulators of gene expression (4)
promoters
DNA sequences that are binding sites for proteins e.g enhancers + silencers
enhancers - increase rate of transcription
silencers - decrease rate of transcription
Define introns
DNA base sequences in eukaryotic genes that are removed at end of transcription
Define telomeres (3)
repetitive sequences that protect ends of chromosome.
ensure that DNA is replicated correctly
every cell division = telomeres lose short stretches of DNA
Features of post-transcriptional modification (3)
mRNA must be prepared for translation
genes contain non-coding information –> must be removed
only for eukaryotes
Procedure of post-transcriptional modification (5)
transcription - synthesis of pre-mRNA
addition of a 5’ cap + poly-A tail - protect the mRNA molecule from degradation by stabilising ends
5’ cap = modified nucleotide added to 5’ end of RNA
poly-A tail - 100-200 adenine molecules added to 3’ of RNA
splicing - removes (excises) introns and joins (ligates) exons to form mature mRNA.
Define alternative splicing (2)
gene can be spliced in multiple ways by combining different exons and omitting others
creates different versions of proteins with different functions
Define initiation stage of translation (6)
Translation starts - 5’ terminal of mature mRNA binds to small ribosomal subunit at mRNA binding site
all mRNA have start codon (AUG) which can be linked to the initiator tRNA
This specific tRNA always carries methionine - all proteins start with this amino acid
ribosome moves along mRNA until it finds the start codon
anticodon of the initiator tRNA (amino acid methionine) binds to codon of the mRNA
large ribosomal subunit joins
Features of post-translational modification (3)
polypeptides synthesised by ribosomes on the rough endoplasmic reticulum are packaged in vesicles
vesicles carry polypeptides to the Golgi apparatus.
modifications carried out in Golgi apparatus
Recycling of amino acids by proteasomes
unneeded/damaged proteins can be broken down + recycled for amino acids
carried out by proteasome (protein complex)
hydrolyses proteins by breaking the peptide bonds between amino acids
Function of recycling amino acids by proteasomes (3)
proteome = total proteins made within body
production of proteins + large supply of amino acids needed to maintain proteomes
provides amino acids to do this
