Lecture 3 - Making Proteins Flashcards
Structures of proteins
- Primary structure: amino acid sequence
- Secondary structure: hydrogen bonds between amino acids form alpha helices or beta sheets
- Tertiary structure: 3D structure of the protein, a single polypeptide chain
- Quaternary structure: two or more polypeptides aka protein-complex
The Central Dogma
DNA => RNA => Protein
transcription: RNA polymerase uses DNA as a template to produce pre-mRNA
translation: a ribosome builds the protein molecule (polypeptide) from a mature mRNA
protein is encoded in a gene
Where is ribosomal RNA encoded?
in a nucleolus
What does RNA polymerase do?
it catalyzes the chemical reactions that synthesize RNA from a DNA template
What are the 3 types of RNA polymerases?
- RNA polymerase I: rRNA genes
- RNA polymerase II (**): mRNA, snRNA, and snoRNA genes
- RNA polymerase III: tRNA and 5S rRNA genes
What’s at the active site of RNA polymerase? What does RNA polymerase do?
- active site has 2 DNA strands and an RNA strand
- two DNA strands form a double helix at the top
- RNA polymerase separates the 2 DNA strands in the middle and builds an RNA strand
- the 2 DNA strands come back together
What are the 4 types of RNAs mentioned in class?
- mRNAs: messenger RNAs, code for proteins
- rRNAs: ribosomal RNAs, form basic structure of ribosome; catalyze protein synthesis
- tRNAs: transfer RNAs, adaptors between mRNA and amino acids
- snRNAs: small nuclear RNAs, function in nuclear processes
What is the TATA box?
- a DNA sequence primarily composed of T and A nucleotides
- typically located about 30 nucleotides upstream from transcription start site
- TATA binding proteins (TBPs) recognize the TATA box
What are general transcription factors?
a set of proteins that RNA Polymerase II requires
- their point is to start transcription
Where does the RNA Polymerase II and the rest of the general transcription factors assemble?
at the promoter
Nuclear pore complex
- where mRNA leaves the nucleus from
- particle movement by NPC is controlled
- mRNA, ribosomes, and proteins leave the nucleus through the NPC
- protein import also happens through the NPC
How does a ribosome translate information from the mRNA into a polypeptide?
- 2 subunits lock together with the mRNA strand locked inside
- ribosome then walks down the mRNA and translates the nucleotides into amino acid chains
- 3 nucleotides (codon) = one amino acid
What is the catalytic site of the ribosome?
in the large subunit
contains the active site of the ribosome: the site that creates the new peptide bonds when proteins are synthesized
where amino acids are added => where proteins are made
What does the small subunit of the ribosome do?
finds a mRNA strand and ensures that each codon pairs with the anticodon
What does tRNA do?
translates the mRNA into amino acids
- tRNAs are a link between the mRNA molecule and the growing chain of amino acids
- anticodons and codons
What stops translation?
Translation termination factor
Why do cells have a nucleus?
RNA must be spliced to remove untranslated regions from mRNA
- exons = part of RNA that code for proteins
- introns = regions residing within a gene but does not remain in the final mature mRNA
if mRNA was not spliced in nucleus, it would be translated before being spliced
What is the protein responsible for splicing mRNA
spliceosomes cut up the exons and reconnect them to produce the mRNA molecules that are used to make proteins
- if this doesn’t happen, proteins will be faulty
- splicing allows multiple proteins to be encoded in a single gene
