D1.2 Protein Synthesis Flashcards
Definition
mRNA
messanger RN
made as a strand that is complementary to template strand of DNA, it therefore has opposite bases (including uracil)
tRNA
transfer RNA
carries amino acids to the ribosomes where they are bonded together to form polypeptide chains
Where does transcription happen in euk. and prok.?
eukaryotes = inside nucleus
prokaryotes = cytoplasm
rRNA
ribosomal RNA
found in ribosomes and codes mRNA into amino acids
Transcription outlined
- Helicase breaks H bonds in region of DNA => seperates bases
- RNA polymerase moves template strands
- RNA polymerase matches complimentary RNA nucleotides (C & G , A & U)
- RNA nucleotides bind to form pre mRNA
- DNA behing RNA polymerase rejoins into double helix
- when RNA reaches stop codon = chain is terminated = pre mRNA detaches
sense and antisense strand
sense= other strand
antisense (created in 5 to 3, BUT starts at 3 to 5 on the DNA strand it is coding on)= strand where mRNA is built
Stages of transcription
- Initiation= RNA polymerase binds to DNA at start of gene = seperates two DNA sztrands by breaking H bonds
- Elongation stage = RNA polymerase build mRNA on one DNA strand
- Termination stage = terminator sequence in DNA is reached = mRNA released
mRNA facts
when a polypeptide is required = triplet code converted to mRNA
- it is recyced when no longer needed (broken down by nucleases)
- single stranded
- contains ribose sugar
- contains uracil
Definition
Translation
after transcription, it is the process by which mRNA combines with ribosomes where proteins are built
Translation outlined
- mRNA attaches to ribosomes of methionine (AUG)
- tRNA with complementary anticodon attaches to mRNA
- tRNA is attached to amino acid
- ribosome moves along mRNA bringing in 2 tRNA at one time
- enzyme & ATP used to join amino acid with peptide bond
- first tRNA released = collects other AA = repeated until stop codon
- many ribosomes can travel along mRNA at same times = polysome
tRNA facts
- small
- single stranded
- clover shaped
- each tRNA can carry different AA
stability of protein synthesis main molecules
mRNA<tRNA<DNA
Triplet
3 nucleotide bases in DNA
anticodon
3 bases at opposite end of tRNA that complementarily bind to codon on mRNA
Codon
3 nucleotide bases in RNA/protein
central dogma of molecular biology
theory that explains how genetic information flows from DNA to RNA to produce a biologically functional product
How many times does each base exist in one unit of codons and triplets
only once
genetic code is non overlapping= each base is only in one codon/triplet
genetic code facts
- sequence of nucelotides
- triplet code (found by francis crick)
- non overlapping
- degenerate => most AA have more than one triplet code
- universal= same base triplet code for same AA in all living organisms
point mutation
Can occur during DNA replication or transcription and involves a single nucleotide base being altered, inserted, or deleted in a DNA or RNA sequence
frameshift mutation
addition or deletion of a base that causes a shift in the reading frame
Sickle Cell Anemia
- blood cells are in sickle shape instead of biconcave disk
- causes heart stroke/attack, bone malformation, pneumonia
- due to single base substitution of A to T
- 6th triplet changes from GAG (GLU) to GTG (VAL)
- prim & second structure of Beta subunit is altered
- quaternary structure of haemoglobin changes
- fibres are deformed
- long fibres poke into cell membrane = distorts shape
- ability to carry oxygen decreases
- block blood vessels
- puts strain on liver as it removes cells
- bone marrow has to continuously produce more
Immediate effects of Sickle cell anemia
- long fibres poke into cell membrane = distorts shape
- ability to carry oxygen decreases
- block blood vessels
- puts strain on liver as it removes cells
- bone marrow has to continuously produce more
Controlling transcription and translation
Transcription
- limiting amount of mRNA produced from particular gene
- post transcriptional events = regulate translation of mRNA
Controlling transcription and translation
Directionality
Transcription= RNA polymerase builds mRNA 5 to 3
Translation= mRNA moves through ribosomes in 5 to 3 & only fits when orientated correctly
Controlling transcription and translation
Initiation of transcription at promoter stages
- RNA can only bind at promoter regions
- transcription factors bind to promoter regions = allows RNA polymerase to bind
- without TF = gene cannot be transcribed
Controlling transcription and translation
Non coding sequence
- 98% of human genome is non coding
Made up of - regulators of gene expression
- Introns = in eukaryotes; removed after transcription
- telomers = found at ends of chromosomes
- genes for tRNA and rRNA
Modifications and splicing
based on fact that mRNA needs to be modified before translating
* pre mRNA contains two regions = exons and introns
* mRNA contains only one region = exons
Introns are removed by spliceosomes (large protein i n nucleus)
Exons are joined together
Exons and introns
exon= protein coding region
introns = non protein coding region
Alternative splicing
gene is spliced in multiple ways by combining different exons
=> creates different versions of proteins
=> Increased protein diversity from the same DNA
Binding sites within protein production
P site= initiator tRNA binds there
A site = where incoming tRNA binds which is added to growing chain
E site = tRNA moves here after transferring AA to growing chain and exits ribosome
Steps of ribosomes making proteins
- Initiation: 5’ of mRNA binds to small ribosomal subunit
- anticodon of intiator tRNA (carrying MET) binds to codon of mRNA
- large ribosomal unit joins to assemble
how proteins gain fucntionality
- formed polypeptide packaged into vesicle by RER
- moves to golgi apparatus
=> post-transformational modification
Proteasome
total of all proteins made and used by the body
How Insulin is made
- 4 sections= A chain, B Chain, c peptide, signal peptide
- pre proinulin enters through RER
- signal peptide is removed
- remaining pp= proinsulin
- disulfide bridges form between A chain & B chain
- Proinsulin is packaged into vesicle -> golgi
- C peptide is removed
- mature insulin remains
Proteasomes function
uneeded/damaged proteins are broken down & recycled by hydrolysis
=> cell can maintain AA conc. & supply
Translation baby language
- mRNA binds to ribosome.
- tRNA brings amino acids to ribosome.
- Peptide bonds form between amino acids.
- Ribosome moves along mRNA until stop codon reached.
Outline the structure and function of the promoter regions of DNA.
- short DNA sequence (typically TATA box)
- binding site for RNA polymerase and other transcription factors
- initiating transcription of the gene
Describe the initiation of transcription, including the role of the promoter sequence, transcription factors, and RNA polymerase.
- transcription factors bind to the promoter region of a gene
- RNA polymerase at the start site
- unwinds the DNA
- synthesizes mRNA from the template strand in the 5’ to 3’ direction.
Activator sequences
bind activator proteins that increase transcription of a gene.
Repressor sequences
bind repressor proteins, which decrease or inhibit transcription
transcription factors
proteins that bind to specific DNA sequences, like the promoter, to initiate or regulate the process of transcription.
five functions of noncoding DNA sequences
Regulation of gene expression (e.g., promoters, enhancers).
Splicing control (e.g., sites for spliceosomes).
Structural roles (e.g., telomeres, centromeres).
Developmental regulation (e.g., transcription factor binding sites).
Reservoir for genetic variation.
location and timing of post-transcriptional modification of RNA.
- nucleus before mRNA leaves to the cytoplasm for translation.
- 5’ capping (methylguanosine cap).
- Poly-A tail addition (adenine residues at the 3’ end).
- RNA splicing (removal of introns and joining of exons).
5’ cap
- protects the mRNA from degradation
- helps the mRNA bind to the ribosome for translation
- helps in transporting the mRNA out of the nucleus.
poly-A tail.
- stability
- mRNA lifespan.
RNA splicing
Spliceosome removes introns, and joins exons
reasons why proteins typically exist for a relatively short time within a cell.
- Rapid degradation via the proteasome system.
- Changes in cellular conditions (e.g., stress).
- The protein’s role in short-term functions.
- Post-translational modifications signaling degradation.
role of activating enzymes in translation
- ATP hydrolysis provides energy for AA attachement
- attach specific AA to 3’ end
- done repeatedly
