Protein Synthesis Flashcards
What is Protein Synthesis?
the process of making new proteins
Where are the instructions for synthesizing proteins found?
in DNA
What are Genes?
sequences of DNA that code for protein
protein synthesis is how genes are expressed
What are the two stages of Protein Synthesis?
Transcription and Translation
Describe Transcription
the first stage of protein synthesis
the DNA template carrying the protein code is “transcribed” into mRNA (messenger RNA)
What does the enzyme RNA Polymerase do?
RNA Polymerase attaches to the Promoter and begins breaking apart hydrogen bonds at the promoter site
similar to helicase in DNA Replication
What is a Promoter?
the beginning region of the gene that allows for protein attachment
like a airport landing pad for RNA Polymerase
Describe the TATA Box
the TATA Box is a promoter sequence that is very common (found in 25% of human genes)
( 5’ - TATAAA - 3’ )
What bond to the complimentary base on the DNA template?
Free RNA nucleotides hydrogen bond to the complimentary base on the DNA Template
RNA does not contain Thymine
What base is used in RNA, that replaces Thymine?
Uracil
it’s identical to thymine but has an extra methyl group on its base
(still a pyrimidine)
How does RNA join the RNA Nucleotides together?
by forming the sugar-phosphate backbone
Describe the 5’ Cap
a 5’ cap is added to the first RNA nucleotide prevent degradation
Describe the Poly (A) Tail
a long strand of adenosine nucleotides
the tail protects the RNA from being degraded at the 3’ ends
(similar to telomeres)
also allows for transport across the nuclear envelope (security pass)
What is Polyadenylation?
the process of adding a poly (a) tail
What happens after the RNA strand is formed?
helicase breaks the RNA-DNA hydrogen bonds,
this frees the RNA strand from the nucleus
this RNA strand is called mRNA
Why is mRNA called mRNA?
it is a messenger that transports the protein instructions from the nucleus to the cytoplasm (where protein is made)
O ———————————————AAA
5’ Cap mRNA poly (a)
tail
What happens to mRNA before leaving the nucleus?
it undergoes RNA Splicing
What are Introns
sequences of RNA that don’t get converted into protein
What are Exons?
RNA sequences that code for proteins
What is RNA Splicing?
The process of removing Introns, leaving behind the Exons
Exons are then spliced (glued) together to form the final translated form of the mRNA Strand
O————————— AAA + Introns
Exons
Where does RNA Splicing take place?
at the Spliceosomes
What are Spliceosomes?
molecules containing a combination of RNA and Proteins, (similar to ribosomes)
located within the nucleus
Describe Translation
the second and final stage of protein synthesis
where the mRNA code is used to make new proteins
What organelle is responsible for performing Translation?
the Ribosomes
Where does Translation Occur?
anywhere ribosomes are found
in the cytoplasm
or
along the Rough ER
What is the ratio that the Ribosomes are composed of?
one third protein
two thirds rRNA (ribosomal RNA)
Where is rRNA synthesized?
in the nucleolus
rRNA is assembled into ribosomes in the cytoplasm
What are the two subunits that Eukaryotic Ribosomes contain?
40S subunit (small)
60S subunit (large)
What is the 40S subunit responsible for?
attaching and reading the mRNA
What is the 60S subunit responsible for?
recruiting tRNA and amino acids
How does mRNA enter the ribosome?
through the 40S, 5’ end first
How do ribosomes read mRNA?
three nucleotides at a time
(codon)
What is a Codon?
a three letter sequence of mRNA
Describe the Start Codon
translation doesn’t occur until the ribosome reaches the start codon
the start codon is always AUG, which codes for Methionine
What is 5’ Untranslated Region?
everything before the start codon
(5’ UTR)
When does translation stop?
translation stops when the ribosome reaches a Stop Codon
(UGA, UAA, or UGA)
What is the 3’ Untranslated Region?
(3’ UTR)
everything in between the stop codon and the Poly(A) Tail
What is the coding region?
the region between the 5’ UTR and the 3’ UTR, containing all Exons
using the coding region, the 60S recruits tRNA (transfer RNA)
What does tRNA contain?
Anti-Codons at one end, and a the matching Amino Acid at the other
What are Anti-Codons
a three nucleotide sequence that complements the mRNA codon
A + U and G + C
Describe how Codons correspond with amino acids
Each codon (except stop codons) correspond with a single amino acid
some amino acids can be coded for by multiple codons
Where do the tRNA transfer the amino acids?
once in the ribosome, the tRNA transfer the amino acid to the growing polypeptide
polypeptide: a group of amino acids
How are proteins synthesized?
(direction)
Proteins are synthesized from the
N-Terminus (amino end) to the
C-Terminus (carboxyl end)
What happens once the stop codon has been reached?
the ribosome detaches and the new protein is released in the cytoplasm
How many Amino Acids are used by humans and how do they differ?
there are 20 amino acids used by humans
they differ in their R-Group (side chain)
What does the Amino Acid Composition affect in a protein?
A proteins :
shape,
hydrophobicity
charge,
solubility
enzymatic abilities
What is Methionine?
the first amino acid in every protein
always first because it is coded for by the AUG start codon
What is so special about Proline?
it causes the N-C-C backbone to kink
Describe the Essential Amino Acids
there are 8 essential amino acids that can’t be synthesized by the body
they have to be acquired by protein in our diet
non-essential amino acids can be produced in the body
What are the three ways Mutations can be classified as to whether they :
help the organism - advantageous
harm the organism- deleterious
have no effect - silent /neutral
Mutations can also be classified by whether a nucleotide is :
added - insertion
removed - deletion
changed - substitution
Describe Missense Mutations
substitution mutations where the change in the nucleotides alter one of the amino acids in a protein
Describe Nonsense Mutations
substitution mutations where the new nucleotide causes an amino acid to be replaced by a stop codon
Describe Frameshift Mutations
insertion or delete mutations that cause all subsequent amino acids to be altered
How is gene expression controlled?
it is controlled by a result of genetics and the environment
as well as the genes themselves
(genetic code)
What is Epigenetics?
the study of how gene expression is altered through factors other than the DNA Code
What happens when Gene Expression is increased?
higher rate of protein synthesis
What happens when Gene Expression is decreased?
lower rate of protein synthesis
What is the most common way gene expression is decreased?
through Methylation
Methylation —> the process of adding a methyl group to DNA so that RNA polymerase can’t easily attach
Explain what Epigenetics explains
that all cells in an individual contain identical DNA,
epigenetics is what makes each cell type distinct from the other
