Proteins Flashcards
Features if genetic code
Non overlapping : each base in sequence only read once
Universal : each triplet codes for same amino acid in all organisms
Degenerate : most amino acids coded for by more than one triplet
Process of protein synthesis
DNA provides the instructions in the form of long sequence of bases
Complimentary section of this sequence is made in form of molecule (PRE-mRNA) aka transcription
PRE-mRNA is spliced to form mRNA
mRNA is used as template to which complementary tRNA attach and amino acids they carry are linked to form polypeptide aka translation
Transcription
Hydrogen bonds between DNA bases break
Only one strand acts as template
Free RNA nucleotides align by comp base pairing
In RNA uracil base pairs with adenine
RNA polymerase joins nucleotides by phosphodiester bond
Pre mRNA is spliced to form MRNA
Role of RNA polymerase
Moves along template DNA strand and joins RNA nucleotides by phospohdiester bond formation
Role of DNA helicase
Breaks hydrogen bonds between bases causing them to separate and exposé’s nucleotide bases
Describe the process of semi-conservative replication of DNA.
- DNA belicase breakes hydrogen bonds
- both strands act as templates
- Free nucleotides attach by complimentary base pairing
- DNA polymerase joins nudeolides to new DNA strand
- phosphodiester bond forms between nucleotides by c. reaction
DNA replication
DNA helix unwinds by DNA helicase which breaks hydrogen bonds between bases
New complimentary nucleotide bases bond to eo using DNA polymerase
DNA ligaments catalyses formation of phosphodiester bonds
Each molecule DNA winds up again creating two identical helices
Genetic
Refers to the way the info about sequence of amino acids is coded for by the bases on mRNA
Genome
Entire set of genes present in a cell/ organisms
Proteome
The entire complement of proteins that can be expressed from genes
Coding for amino acids
3 nucleotide bases
The codons can translate for 20 amino acids
Triplet codons do not overlap
Features for Coding for amino acids
Different codons can translate for same amino acid = degenerate
The order of codons determines the amino acid sequence
Start codon (AUG) MET
Terminates with a stop codon
Code is universal
Describe a Gene
Base sequence of DNA that codes for amino acid sequence of a polypeptide or functional RNA
How change in one base along a DNA molecule may result in an enzyme becoming nonfunctional
Different base may code for different amino acid
Sequence of amino acids in polypeptide produced will be different
Change in primary structure
Enzyme shale will be different and may not fit S
E-S complexes cannot be formed
mRNA
Used to make a copy of the genetic code contained on the DNA molecule and transfer to ribosomes
- mRNA is complementary to the DNA it codes for
- Single strand so can leave nuclear pore
- mRNA associates with ribosomes to initiate second stage of protein synthesis
tRNA
Used to bring specific amino acids to the mRNA
Anticodon is complementary to mRNA codon
Allows ribosomes to link amino acids and build polypeptides
rRNA
used for making ribosomes that are sites for protein synthesis
Transcription
Process by which RNA sequence is produced for DNA polymerase using RNA polymerase
Process or transcription
1.DNA helicase breaks hydrogen bonds on section of DNA containing gene for desired protein
2.RNA polymerase binds to site on the DNA at start of gene
3.Free complimentary nucleotides are epxposed to RNA polymerase moves along antisense strand from 3’ to 5’
4.The RNA polymerase joins nucleotide on the exposed template strand form pre-mRNA
5.The DNA bases rejoin as RNA polymerase moves along
6.
Process or transcription
1.DNA helicase breaks hydrogen bonds on section of DNA containing gene for desired protein
2.RNA polymerase binds to site on the DNA at start of gene
3.Free complimentary nucleotides are epxposed to RNA polymerase moves along antisense strand from 3’ to 5’
4.The RNA polymerase joins nucleotide on the exposed template strand form pre-mRNA
5.The DNA bases rejoin as RNA polymerase moves along
6.RNA sequence synthesized = RNA polymerase detaches from DNA
7.Pre-mRNA detaches from DNA
8.pre-mRNA can then be spliced and leaves nuclear pore
How does transcription differ from replication
Only short segment of DNA is unwound not the whole strand
As RNA is being made arena polymerase not DNA is used
Only 1 strand of DNA is read (antisense)
Splicing pre-mRNA
Bulk of euk genome has DNA sequences don’t code for proteins and not transcribed
Introns = non coding region
Exons = coding regions
Both present in pre-mRNA and removed by enzymes during transcription = mature MRNA which leaves nucleus to be translated into polypeptides
Enzymes present in transcription and what they do
DNA helicase - breaks hydrogen bonds and unwinds section of DNA and exposes nucleotides
RNA polymerase - adds complimentary RNA nucleotides to form pre-mRNA
What happens when the RNA polymerase attaches to the DNA at the start codon?
Forms phosphodiester bonds between RNA nucleotides on the pre-mRNA strand
Translation
Process when the genetic information encoded in mRNA is translated into a sequence of amino acids in a polypeptide chain.
What happens after mRNA leaves the nuclear pore
the mRNA will attach itself to a ribosome. A ribosome is composed of two halves, a large and a small subunit. During translation, ribosomal subunits assemble together on the strand of mRNA.
Subunits
Each compose of RNA molecules and proteins
Small subunits binds to the mRNA
Large subunits has bindings sites for tRNA and catalyses peptide bonds between amino acids
tRNA structure
In the cytoplasm are free amino acids and transfer RNA (tRNA) molecules In the cytoplasm are free amino acids
Short single strand of RNA
Folded into clover and held by H bonds
At one end there’s a site where amino acids can bind to
Other end threee unpaired bases = anticodons
Only binds to specific amino acid
Require energy from ATP
Types of molecules which ribosomes is made
RNA
Nuclei acids
Proteins
rRNA
Primary structure of proteins
Sequence of amino acids that make up polypeptide chain and DNA determines sequence = shape and function of protein
Secondary structure
Arrangement of polypeptide chains into regular repeating structure held tgt by hydrogen bonds can result in a helix or b pleated sheet
Tertiary structure
Level of 3D organization causes by bonding between R groups of nearby acids includes disulfide ionic and hydrogen bonds
Quaternary structure
Consist of two or more chains of polypeptides a prosethic group can be associated
Chaperone proteins
Folding of protein depends on position and type of R-groups which determines which bonds are made
Chaperons(HSP 70) bind to hydrophobic regions of polypeptides and prevent them from interacting with other hydrophobic regions and prevent misfolding
HSP 60 allow polypeptide chains to fit within them and isolate them
What’s an anticodon
Triplet of bases on tRNA which is complementary to binding site on mRNA.
two differences between the structure of mRNA and the structure of tRNA (5)
MRNA does not have H-bonds / base pairing, tRNA does OR mRNA is linear / straight chain, tRNA is cloverleaf;
• MRNA does not have an amino acid binding site, tRNA does;
• MRNA has more nucleotides
• Different mRNAs have different lengths, all tRNAs are similar / same in length;
• MRNA has codons, tRNA has anticodons;
Describe how translation leads to production of a polypeptide
MRNA associates with a ribosome
Ribosome moves to / finds the start codon;
TRNA brings / carries the appropriate / specific amino acid;
Anticodon on tRNA is complementary to the codon on mRNA
Ribosome moves along to the next codon
process repeated and amino acids joined using energy from ATP to form polypeptide.
tRNA structure
In the cytoplasm are free amino acids and transfer RNA (tRNA) molecules In the cytoplasm are free amino acids
Short single strand of RNA
Folded into clover and held by H bonds
At one end there’s a site where amino acids can bind to
Other end threee unpaired bases = anticodons
Only binds to specific amino acid
Require energy from ATP
Describe the structure of proteins.
primary structure is a) chain of amino acids/sequence of amino acids
Secondary structure formed by interactions between amino and carboxyl groups and hydrogen bonds formed
Tertiary structure is folding up of the polypeptide
Stabilized by disulfide bridges/hydrogen/ionic bonds
Quaternary is when more than 2 polypeptide subunits join
Conjugated proteins combine with other nonproteins
