Protein Synthesis and Control Flashcards
Define anti-codon
A sequence of three adjacent nucleotides on a molecule of transfer RNA (tRNA) that is complimentary to a particular codon on a messenger RNA molecule
Define codon
A sequence of three adjacent nucleotides in messenger RNA (mRNA) that codes for one amino acid.
Define deletion mutation
A nucleotide is lost from the normal DNA sequence. This results in all the nucleotide after this point being read in the incorrect order This is known as a Frame shift.
Define DNA helicase
An enzymes that acts on a specific region of the DNA molecule to break the hydrogen bonds between the bases causing the two strands to separate and expose the nucleotide bases.
Define DNA replication
The process when the double helix of a DNA molecule unwinds and each strand acts as a template on which a new strand is constructed.
Describe messenger RNA
The RNA that transfers the DNA code from the nucleus through the nuclear pore to the cytoplasm. The code it contains is used by ribosomes to determine the order in which the amino acids should be bound to form a protein.
Define mis-sense mutation
The base change results in in a different amino acid being coded for. The polypeptide produced will differ in a single amino acid. The consequence will depend on where the amino acid was.
Define mutation
A change in the sequence of bases in DNA
Define non-sense mutation
A base change that has resulted in the formation of a stop codon. The production of the polypeptide will be stopped prematurely leading to a non functional protein.
Define nucleotides
Complex chemicals made up of an organic base, a sugar and a phosphate. They are the basic units of DNA and RNA.
Define RNA polymerase
Enzyme that joins together nucleotides to form messenger RNA during transcription.
Define silent mutation
A substituted base that still codes for the same amino acid. There is no effect on the order of amino acids so no alteration of the polypeptide formed.
Define transcription
Formation of messenger RNA molecules from the DNA that makes up a particular gene. This is the first stage of protein synthesis
Describe transfer RNA
A small singe stranded chain of RNA folded into a clover leaf shape with one end of the chain extending beyond the other. Each molecule carries a single amino acid whose codon binds to its Anticodon.
Describe translation
When mRNA is used as a template by ribosomes to which complementary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide chain.
Define double helix
DNA nucleotides join together between the phosphate group and the sugar creating a sugar phosphate backbone. 2 DNA polynucleotides join by hydrogen bonding between the bases by complementary base pairing. 2 strands wind to form the double helix.
Give the process of transcription
- DNA helicase breaks hydrogen bonds
- One strand used as a template for mRNA
- RNA polymerase adds complementary base pairs
- mRNA moves out of the nuclear pore and to the ribosome
Give the process of translation
- tRNA carry amino acids to the ribosome
- tRNA with a complementary anticodon attaches itself to the mRNA
- The second tRNA attaches itself to the next codon in the same way
- the 2 amino acids join via peptide bonds
- the 1st tRNA leaves and so on until a stop codon is reached
How do you control protein synthesis
By altering the rate of transcription of genes
Define operon
A section of DNA controlling structural genes, control elements and a regulatory gene
Define regulatory gene
A protein which binds to DNA and switches genes on or off by increasing or decreasing the rate of transcription
What determines whether the transcription factor can bind to the DNA or not
The shape of a transcription factor
What is the lac operon
an inducible protein
What are the two substances e coli can respire
glucose
lactose
Give 2 reasons the e coli doesn’t always make the necessary enzymes for lactose respiration
Making proteins that are not essential at that time will tie up resources such as amino acids
Uses a lot of energy unnecessarily
What are the 2 lactose specific enzymes
Lactose Permease
Beta-Galactosidase
What is the function of beta-galactosidase
Catalyses the hydrolysis of lactose into glucose and Galactose
What is the function of lactose permease
Increases the cell’s permeability to lactose so it can take in more
lactose from the surrounding environment
What are the 5 regions on the lac operon
i p o z y
What is the i region
Regulatory Gene
which codes for a
repressor protein
What is the p region
p = Promoter region which
binds RNA Polymerase
What is the o region
Operator region which
binds the repressor protein
What is the z region
z = Structural gene for
Beta-Galactosidase
What is the y region
y = Structural gene for lactose permease
Describe what happens in a glucose rich environment/Lactose low environment
- The regulatory gene undergoes transcription and translation and a repressor
protein is synthesised - The repressor protein has 2 binding sites, one of which binds to lactose the
other to the operator region. - In the absence of lactose the repressor protein binds to the operator region and
blocks part of the promoter region of the lac operon. - This prevents RNA Polymerase binding to the promoter region
- This therefore prevents transcription of the structural genes Z for BetaGalactosidase
and Y for Lactose Permease.
Describe what happens in a glucose low environment/Lactose rich environment
- The regulatory gene undergoes transcription and translation and a repressor
protein is synthesised - The repressor protein has 2 binding sites, one of which binds to lactose the
other to the operator region. - In the presence of lactose the repressor protein binds to the lactose, which
alters the shape of the repressor protein. - The repressor protein can now no longer bind to the operator region.
- This leaves the promoter region free to bind RNA Polymerase
- This therefore allows the transcription of the structural genes Z for BetaGalactosidase
and Y for Lactose Permease. - Beta-Galactosidase catalyses the hydrolysis of lactose to glucose and
galactose. - Lactose permease increases the cell’s permeability to lactose so it can take in
more lactose from the surrounding environment
What controls the development of body plan
Homeoetic genes
Define homeobox genes
a type of gene which contains within its genetic code a
sequence of 180 bases, which is referred to as a Homeobox
What are homeobox genes organised in
Hox clusters
What does vitamin A activate
Homeotic genes in vertebrates
Why should pregnant women avoid too much vitamin A
It can interfere with normal gene expression (particularly in fetus heads)
Define apoptosis
Programmed cell death
Give 2 molecules controlling apoptosis
Hormones
Cytokines
Growth factors
Nitric Oxide
Describe the process of apoptosis
- Enzymes digest the cytoskeleton
- Cytoplasm becomes dense as organelles become more tightly packed together
- Blebs form (bulging)
- Chromatin (DNA & proteins) condense and the nuclear envelope breaks
- DNA fragments
- The cell breaks apart forming apoptotic bodies (vesicle like structures)
- These bodies package the harmful hydrolytic enzymes preventing damage to
other cells - Phagocytosis of the cellular debris, some of which can be recycled.
Define necrosis
premature cell death
Give 2 causes of necrosis
o Infection
o Trauma
o Toxins
What is the hayflicks limit
This refers to the believed number of mitotic divisions a cell can undergo before it is
highlighted be destroyed and its components recycled.
50 divisions
What disease is an example of when the hayflicks limit is not stuck to
Cancer (uncontrolled cell division)
Define mutation
changes to the sequence of DNA nucleotides in a gene
What cells do mutations occur in to affect the offspring
gametes
What are the 3 levels that mutations can occur at
DNA
Gene
Chromosome
Define genetic code
sequence of Nitrogenous bases (DNA) held in the gene
How does cyclic AMP work
Activates proteins by altering their three-dimensional
structure
