8. DNA, genes and protein synthesis Flashcards
what two things do genes code for the production of?
amino acid sequence of a peptide
functional RNA
what is meant by the term ‘degenerate code’
several codons code for the same amino acid
what are the non-coding sections of DNA called?
introns
Name the 4 different bases in DNA, and their complementary pairings
Guanine cytosine adenine thymine G-C A-T
Which base is switched to uracil in RNA
Thymine
define genome
the complete set of genes in a cell
define proteome
the full range of proteins a cell is able to produce
define allele
an alternative form of gene
two sister chromatids are joined by what?
centromere
the section of three bases in tRNA which binds to the mRNA strand is called…
anticodon
give the three components of DNA?
deoxyribose, pentose (5) carbon sugar
phosphate backbone
nitrogenous base
What is the difference between the components of RNA and the components of DNA?
RNA contains ribose opposed to deoxyribose
in what process is pre-mRNA created?
transcription
which enzyme is involved in transcription to join RNA nucleotides together?
RNA polymerase
what is the DNA strand known as in transcription?
template strand
what happens to pre-mRNA before it leaves the nuclear envelope?
the introns are removed
when mRNA is in the cytoplasm, which organelle does it attach to for the next stage of protein synthesis?
ribosome
what bond forms between two amino acids in protein synthesis?
peptide bond
what is the role of ATP in translation?
provides energy for bond to form between tRNA and the amino acid
what is the role of tRNA in translation?
carries amino acids to the nucleotide. lines them up in the correct order.
define translation
the process of converting the codon sequence in the mRNA molecule into an amino acid sequence
explain the process of translation.
The mRNA molecule passes out of the nuclear pore after splicing.
A ribosome attaches to the start codon of the mRNA
A tRNA with the complementary anticodon sequence to the first mRNA codon pairs with the codon on the mRNA
The ribosome has two codon binding sites, so two tRNA molecules at a time are brought together
A peptide bond forms between the 2 amino acids on the tRNAs with the use of an enzyme and ATP which is hydrolysed to provide energy
The ribosome moves along the mRNA to the next codon so the first tRNA is released and a new tRNA arrives at the next codon
This continues, with up to 15 amino acids being added each second until a polypeptide chain is built up
what is the term used when talking about a section of a gene in a eukaryote?
allele
what is meant by the term diploid number?
the number of chromomsomes
what is an allele, can you give an example
a version of a gene
e.g blue eyes, green eyes
how do mutations affect genes?
changes in the base sequence of a gene produce a new allele for that gene
this leads to the production of a different polypeptide, and therefore a different protein
this protein may not function properly or at all
what is meant by the term gene?
a section of DNA that codes for one protein
what is meant by the term allele?
a version of a gene
what name is used for the non-coding sections of a gene?
introns
define genome
the complete set of genes in a cell
define proteome
full range of proteins produced by the genome
how does RNA differ from DNA?
ribose nucleotides opposed to deoxyribose
base uracil instead of thymine
single stranded, not double. however can fold into 3-D structures
shorter than DNA
how many different kinds of RNA are there?
3
RNA
tRNA
mRNA
define codon
sequence of 3 bases that codes for an amino acid
what is the general function of RNA?
transfers coded information from the DNA into the cytoplasm where it can be translated into proteins
explain the function of mRNA and some of its essential features
the code for a gene in the DNA molecule is ‘transcribed’ (copied) into an mRNA molecule.
mRNA carries the code for a particular polypeptide from the nucleus to the cytoplasm
can travel through nuclear pores
single stranded helix
short lifetime
explain the function of tRNA and some of its essential features
matches the triplet code in an mRNA molecule to their respective amino acids
only 80 nucleotides long
folds up by complementary base pairing to form a looped clover-leaf structure
on the middle loop there is a triplet nucleotide sequence called the anticodon
anticodon is complementary to one of the possible 64 possible codons on the mRNA
each amino acid is attached to a tRNA with the appropriate anticodon
what does RNA stand for?
ribonucleic acid
what does tRNA stand for?
transfer RNA
what does rRNA stand for?
ribosomal RNA
explain the function of rRNA
together with proteins forms ribosomes
ribosomes have two subunits, small and large, and are assembled in the nucleotides of the nucleus
Describe the process of transcription and translation as a whole
dna unzipped by dna helicase, rna polymerase transcribes pre-mrna from the template strand
stop codon tells rna polymerase to stop and detaches
pre-mrna is made, splicing occurs which removes introns (non-coding) and keeps exons (coding)
mrna binds to ribosome and reads the codons, complementary anticodons are provided by the trna which holds the amino acids
amino acids are bound into a polypeptide chain
describe the process of transcription
rna polymerase binds to a section of the dna
the hydrogen bonds on the dna molecule are broken (also by part of the rna polymerase complex), exposing the bases
the nucleotides on one of the 2 dna strands, known as the template strand, bind to the complementary mrna nucleotides present in the nucleus
rna polymerase moves along the strand, joining the nucleotides together to make a pre mrna molecule
the dna strands re-join behind the newly forming strand of pre-mrna
when the rna polymerase reaches the stop codon it detaches and the pre mrna is complete
What is transcription
the process of making pre-mrna using part of the dna as a template
the dna template strand (strand against which the mrna is complementary) can also be referred to as the coding strand
describe the process of dna replication
dna replication is semi-conservative
dna helicase ‘unzips’ the strand into 2 separate strands (breaks hydrogen bonds)
the dna is reassembled by the dna polymerase in an anti-parallel fashion, 3’ to 5’
once completed the chains are complementary , making 2 identical strands overall
what is the splicing of pre mrna
dna is made up of introns and exons
pre-mrna , dna made up of introns and exons
splicing is the removal of introns to give us functioning mrna
this occurs before translation
difference between introns and exons?
exons - code for proteins
introns - we don’t know what they do exactly, just know that they don’t code for proteins
How can the same sequence of dna code for several different proteins?
after splicing the exon sections can be joined in a variety of combinations and orders.
what can affect splicing of pre-mrna?
mutations
e.g. alzheimer’s disease is caused by splicing failures, so non-functional polypeptides are made
what is translation?
the process of converting the codon sequence in the mrna molecules into an amino acid sequence
mrna leaves nucleus via nuclear pore, then synthesises a polypeptide
describe the process of translation.
the mrna molecule leaves via a nuclear pore after splicing
a ribosome attaches to the start codon of the mrna
a trna with the complementary anticodon sequence to the first mrna codon pairs with the codon on the mrna
the ribosome has two codon binding sites, so two trna molecules at a time are brought together
a peptide bond forms between the 2 amino acids on the trna with the use of an enzyme and atp which is hydrolysed to provide energy
the ribosome moves along the mrna to the next codon so the first trna is released and a new trna arrives at the next codon
this continues, with up to 15 amino acids being coded each second, until a polypeptide chain is built up.
