dna genes and protein synthesis Flashcards
what is a gene
a gene is a base sequence of DNA that codes for the amino acid sequence of a protein(polypeptide) or a functional RNA
whats the definition for genome
all of the genes that code for a particular species
what is genetic loci
the position of a gene on a chromosome is its locus
what is an allele
each gene can exist in two or more different forms
what is the difference between alleles
different alleles of a gene have slightly different nucleotide sequences but they still occupy the same position (locus) on the chromosome
what is genetic code
the base sequence in a DNA molecule represented by the letters ATCG make up the genetic code. the genetic code is read in triplets of bases or codons
how many bases codes for 1 amino acid
3 bases ( a triplet )
what can some of the triplets code for
start and stop signals, these signals tell us where the individual genes start and stop . this ensures the cell reads the DNA correctly and can produce the correct sequences of amino acids .
whats another feature of start and stop signals
they are complementary to eachother
why is our genetic code read in triplets
there are four bases . if each base coded for an amino acid there would only be 4 amino acids that could be used
however there are 20 different amino acids
if every 2 bases coded for an amino acid then we would have 16 possibilities therefore we have triplet code as we have 64 combinations (4^3) and this results in triplets coding for the same amino acid ( as theres only 20 combinations and we have 64)
what are the 3 main features of genetic code
- degenerate
-non - overlapping
-universal
what is the definition for degenerate
More than one codon codes for each amino acid
whats the definition for non-overlapping
the genetic code is read sequentially. each base is part of only one triplet
whats the definition for universal
in all organisms the same triplet/ codon codes for the same amino acid
- the same triplet always codes for the same amino acid in all organisms
whats non coding DNA
the genome within eukaryotic cells contains many non - coding sections of DNA which does not code for any amino acids
what are the non coding sections called
introns
what are the coding sections called
extons - the parts of a gene that do code for an amino acid
explain how the change in one base along the DNA molecule may result in an enzyme becoming non functional
a different base might code for a different amino acid. the sequence of amino acids in the polypeptide produced would be different .this change to the primary structure may result in a different shaped tertiary structure and therefore the enzyme shape will be different and may not fit the substrate . the enzyme - substrate complex cannot form and so the enzyme is non functional
What are the differences between DNA and RNA
-DNA is Double stranded whereas RNA is single stranded
-DNA contains thymine whereas RNA contains uracil
-DNA contains a deoxyribose sugar whereas RNA contains a ribose sugar
-DNA contains genetic information whereas RNA is used in protein synthesis
-DNA is found in the nucleus , chloroplasts and mitocondria whereas RNA is in the cytoplasm, ribosomes and nucleus
What are the types of RNA
Transfer RNA , ribosomal RNA, messenger RNA
What is protein synthesis
Where a sequence of bases in DNA determines and produces the sequence of amino acids in the proteins of an organism
What’s messenger RNA
mRNA is a single stranded molecule . It is made up of a sugar phosphate backbone and exposed unpaired bases . Uracil bases are present instead of thymine
What is tRNA , transfer RNA
It’s a single stranded RNA molecule . It has a distinctive folded structure with three hairpin loops that form the shape of a cloverleaf . Hydrogen bonds form between some of the bases if complementary
Amino acids bind to a specific region of the molecule
They have an anticodon found on the end and is complementary to a specific codon on the mRNA molecule
What is ribosomal rRNA
A ribosome is made out of rRNA and proteins
Each ribosome consists of two separate RNA-protein complexes
RNA can be of varying sizes , commonly distinguished with small and large ribosome subunits . These rRNAs are vital in recognising mRNA and tRNA thus facilitating their binding and carrying out protein synthesis
what is protein synthesis
the process of making proteins from DNA
what are the two stages
transcription and translation
what happens during transcription
makes a copy of the DNA called mRNA
what happens during translation
where mRNA is read by ribosomes to produce a protein
what are the steps for transcription
1) the DNA in the nucleus is first unwound from the double helix
2) the weak hydrogen bonds between the bases by the enzyme DNA helicase are broken
3) causes two strands to seperate
4) free RNA nucleotides in the nucleoplasm find their complementary base pair on the DNA template strand
5) a hydrogen bond forms between the RNA nucleotide base and the complementary base on the DNA
6) the enzyme RNA polymerase then catalyses the formation of the strong chemical bonds ( phosphodiester bond ) between the ribose sugar and phosphate groups of adjoining RNA nucleotides
7) the messenger pre - mRNA molecule is
formed
8) hydrogen bonds between the bases mRNA and the bases on the DNA break
9) the hydrogen bonds between the complementary bases on DNA reform and the DNA is wound back into a helix
10) after transcription the mRNA strand can be spliced and this means the introns are cut out and the extrons are joined back together
6 marker describe transcription
1) DNA in the nucleus is unwound and DNA helicase breaks the hydrogen bonds
2) the two strands seperate and free RNA nucleotides in the nucleoplasm find their complementary base pair on the DNA template strand exposed bases
3)a hydrogen bond forms between the RNA nucleotide base and the complementary base on the DNA
4) RNA polymerase catalyses the formation of phosphodiester bonds between the ribose sugar and phosphate groups on adjoining RNA nucleotides
5) the pre mRNA molecule is formed
6)hydrogen bonds between the mRNA and DNA strand break
7) hydrogen bonds between the complementary bases on DNA reform and wind back into a helix
8) the pre mRNA strand is spliced and introns are cut out and exons are joined back together to form mRNA
where does transcription occur
in the nucleus
where does translation occur
in the cytoplasm
what is translation
translation is the process where mRNA is read and translated into a protein . it occurs in the cytoplasm / on the ribosomes
and involves tRNA
what are the steps for translation
1) the mRNA leaves the nucleus through a nuclear pore and enters the cytoplasm
2)a ribosome becomes attached to the mRNA
3) the genetic code is read in groups of 3 letters called codons
4)tRNA molecules have specific anticodons for each of the 20 amino acids
5) the complementary anticodon is attracted to the first codon , called an initiation codon on the mRNA and forms a weak hydrogen bond
6) this then repeats with every codon until the mRNA is all read
7)a peptide bond is formed between the adjacent amino acids
8) the first tRNA molecule becomes detached from its amino acid
9) the ribosome moves along the mRNA molecule
10) a stop codon is reached
11) a polypeptide chain has been formed and it can be released into the cytoplasm or other organelles
12) the tRNA molecules are activated after use by recombining with their specific amino acid (requires ATP)
what happens with the polypeptide after protein synthesis
the amino acid chain is then sent to the rough endoplasmic reticulum and is folded through its secondary and tertiary structures to form a protein. then the folded proteins is sent to the golgi apparatus which modifies and packages the protein into a vesicle , this protein is then sent within the cell or outside of the cell where it is needed
what is a proteome or complete proteome
the full range of different proteins the genome can code for or
the number of different proteins that a cell is able to produce at a given time
what 6 points must you include in your translation 6 marker
- mRNA leaves the nucleus through the nuclear pore to ribosome
- tRNA molecules bring amino acids to ribosome
-specific tRNA molecule for specific amino acid
-aniticodon of tRNA is complementary to codon on mRNA
-peptide bonds form between amino acids
-tRNA detaches and collects another amino acid
-ribosome moves along mRNA
Give two structural differences between a molecule of messenger, RNA and a molecule of transfer RNA
MRNA does not have an amino acid binding site whereas tRNA does
MRNA is a straight chain, whereas tRNA is a cloverleaf
Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide
A ribosome attaches to the mRNA and the genetic code is red in codons. The ribosome moves to find the start codon tRNA molecules have specific anticodons for each of the 20 amino acids. The complimentary anti codon is carried and attracted to each codon on the mRNA and forms hydrogen bonds between adjacent amino acids and tRNA molecules detach and pick up another amino acid the ribosome moves along to the next codon on the mRNA molecule and a stop codon is reached a polypeptide is produced
Give the two types of molecule from which a ribosome is made
One of rRNA and one of protein
Describe the role of a ribosome in the production of a polypeptide do not include transcription in your answer
A ribosome attaches to the mRNA strand and moves along allowing tRNA anticodons to attach. two codons can fit at a time and ribosomes catalyses the formation of the peptide bond between amino acids .
Explain why the percentages of bases from the middle part of the chromosome and the end part are different
They have different base, sequences and pre-mRNA transcribed from different DNA
Different sequences of bases code for different proteins. Explain how
A protein is made of a chain of amino acids each amino acid has its own base
How is DNA packed into a chromosome
-DNA molecule combines with histones
-DNA - histone complex is coiled
-coils fold to form loops
-loops coil and pack together to form the chromosome
Suggest the role of the mRNA triplets stop codons
They stop translation and therefore resulting in ribosome detaching from mRNA chain
describe how the production of mRNA in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell
- mRNA in a eukaryotic cell contains introns whereas in a prokaryotic cell does not contain introns and pre - mRNA is produced
