Ch 10 from DNA to Protein Flashcards
Steps of Gene Expression
Production of protein from instruction on the DNA
TRANSCRIPTION = production of mRNA TRANSLATION= production of protein using mRNA, tRNA, and. rRNA
Folding of the protein into the active 3D form
Gene Expression Human Genome
Human Genome contains about 20,000 protein-encoding genes this is only a small part of the genome
Human genome controls protein synthesis
Time speed and location
Central Dogma
Refers to the directional flow of genetic information
Replication
Transcription
Translation
Protein
Viruses have a reverse rRNA it works from RNA to DNA
Nucleic Acids
Two types of nucleic Acids
RNA
DNA
Both consist of sequences of N-containing bases joined by sugar phosphate backbones
DNA
Usually double stranded Thymine as the base Deoxyribose as the sugar (more stable sugar) Maintains proteins-encoding information Cannot function as an enzyme Persists
RNA
Usually single stranded (helix not linear can fold up on it self more variety with shape)
Uracil as a base
Ribose as the sugar (presence of hydrogen makes it more stable)
Carries protein-encoding information and controls how information is used
Can function as an enzyme
Transient
Types of RNA
3 major types
mRNA - messenger RNA
rRNA - ribosomal RNA A Polypeptide made up of ribosomal DNA + protein it is the site that link Amino Acids together
tRNA -transfer RNA brings the amino acids to the ribosome subunit
Other classes of RNA control gene expression
mRNA
Carries information that specifies a particular protein
Produced in the nucleus
Transported to the ribosome
3 nucleotide Codon specifies a particular amino acid
Most mRNA are 500 - 4500 bases long
rRNA
Associated with proteins to make up ribosomes
Ribosomes consist of two subunits that join during protein synthesis
rRNA provides structural support -some are a catalyst (ribozymes)
tRNA
Only 75-80 bases long
The 2-D shape is a clover leaf
The 3-D shape is an inverted L
Has two business ends:
The anticodon forms hydrogen bonds with the mRNA codon
The 3’ end binds the amino acid specified by the mRNA codon
Transcription
RNA is the bridge between DNA and protein
RNA is synthesized from one strand of the DNA double helix, which is called the template strand
The complementary strand is called the coding strand of DNA
Requires the enzyme RNA polymerase
Transcription Factors
In bacteria, operons control gene expression.
In more complex organisms transcription factors control gene expression and link genome to environment
These contain DNA-binding domains
About 2000 in humans
Mutations in transcription factors may cause a wide range of effects
Steps if Transcription
Initiation a cascade of transcription factors bind to the promoter region of a gene
These open a pocket allowing the RNA polymerase to bind just in front of the start of the gene sequence
Elongation RNA polymerase reads the nucleotides on the template strand from 3’ to 5’ and creates an RNA molecule that looks like the coding strand
Termination occurs when sequences in the DNA prompt the RNA polymerase to fall off ending the transcript
RNA Processing
In Eukaryotes mRNA transcripts are modified before they leave the nucleus
- A methylated cap added to 5’ end
- recognition site for protein synthesis - A poly-A tail is added to the 3’ end
- stabilizes the mRNA
3 splicing occurs
- introns are removed (they code for sequence we don’t need)
- Exons are spliced together expressing sequence (code for sequence we need so they are spliced together )
Finally the mature mRNA is sent out of the nucleus
3’ end folds up on itself
Translation (3 steps)
The process of reading the mRNA base sequence and creating the amino acid sequence of a protein
Divided into 3 steps
Initiation The start codon (AUG) attracts an initiator tRNA that carries methionine (initiation complex completes) The A-site is where the new amino acid will enter tRNA forms hydrogen bond
Elongation the second tRNA binds to next mRNA codon first peptide bond forms bet. The two amino acids
tRNA bring in more amino acids as the ribosome moves down the mRNA
A-site holds the newest tRNA
P-site bears the polypeptide chain
Termination occurs when a stop codon enters the A-site of the ribosome
A protein release factor frees the polypeptide
The ribosomal subunits separates and are recycled
E-site is the exit area of subunit
The Genetic Code
It is a triplet code -3 successive mRNA bases form a codon
There at 64 codons including (AUG) one start signal
3 stop signals (UAA,UAG,& UGA)
It is non-overlapping
It is degenerate
-two or more codons may specify the same amino acid
It is universal
-evidence that all life evolved from a common ancestor
Reading frame
A sequence of amino acids encoded for a certain starting point in a DNA/RNA sequence
One or two base added causes a frameshift everything after that added bases is wrong and alters the sequence making it invalid
Polypeptide
Polypeptide can be a couple thousand codons long
Anything after stop codon does not get copied to polypeptide chain and release factor are used to release mRNA and last created tRNA
Multiple copies of a protein can be made simultaneously the closer to the end of the gene the longer the polypeptide
Protein Structure
Protein fold into one or more 3-D shapes or conformations
There are four levels for protein structure
Primary (1) structure is the single polypeptide chain
Secondary (2) structure due to hydrogen bonds are helix or beta pleated sheets doesn’t have to be all one or the other
Tertiary (3) structure interaction with R-groups and determine the shape of the eternal structure
Quaternary (4) structure if made up of multiple polypeptide chain hemoglobin made up of 4 polypeptide chains
Polypeptide is just one chain
Protein can be multiple polypeptide chains linked together
Protein folding
Protein folding begins as translation proceeds
Enzymes and chaperone proteins assist
Should a protein midfield an “unfolded protein response” occurs
-protein synthesis slows or even stops
Protein Misfolding
Misfolded proteins are tagged with ubiquitin
Then, they are escorted to a protea some, a tunnel-like multi protein structure
As the protein moves through the tunnel it is straightened as dismantled
Protea some also destroy properly-folded proteins that are in excess or no longer needed
Prions
Prion protein (PrP) can fold into any several conformations
One conformation is aberrant
-moreover it can be passed on to other prions upon contact, propagating like an “infectious” agent
Prion Misfolded proteins that cause many infection disease no nucleic acids unique ability when come in contact when come in contact with normal protein they change its shape. They cluster together
Prions do not denature even when you cook it still stays alive
Splicing
Introns are intervening sequences of RNA that do not code for a polypeptide and must be spliced/cut out.
