DNA, genes, protein synthesis Flashcards
Describe the DNA in a eukaryotic cell
Packaged as chromosomes in the nucleus and is linear, and associated with proteins called histones, together forming chromatin.
Describe the DNA in a prokaryotic cell
Short, circular, and not associated with proteins, condenses by supercoiling.
There are 2 grooves in a double helix of DNA, what are their names?
Major groove
Minor groove
What protein causes DNA to coil to form chromosomes?
Histone
DNA winds itself around this and it also helps to support DNA.
How many chromosomes do we have?
46 individual chromosomes, (diploid number)
What is a homologous pair?
A pair of matching chromosomes ( x x) .
-Have the same genes but could have different alleles.
Define mRNA
Messenger ribonucleic acid, read by ribosomes in protein synthesis, single stranded.
Define codon
A sequence of 3 adjacent nucleotides in mRNA that codes for one amino acid.
What is Transcription?
The formation of mRNA molecules from the DNA that makes up a particular gene.
Define genome
The entire set of DNA instructions found in a cell.
Define proteome
The entire set of different proteins expressed in a genome, cell, tissue, or organism at a certain time.
What is Translation?
The conversion of the information in mRNA to make a polypeptide.
What is the ‘Genetic Code’?
The sequence of bases along its DNA, and has thousands of sections called genes, each coding for a specific polypeptide.
The genetic code is ‘universal’, what does this mean?
Has the same sequence for all organisms.
What are some differences between DNA and RNA?
RNA:
-Ribose
-Single stranded
-Uracil base
-Single nucleobase
DNA:
-Deoxyribose
-Double stranded
-Thymine
-Base pairs
What is a triplet code?
3 bases that make an amino acid
The triplet code is ‘degenerate’, what does this mean?
Each amino acid is coded for by more than one triplet.
What does ‘non-overlapping’ mean?
Each base is only read once
Briefly outline the 4 steps of protein synthesis
- Transcription of the gene in the nucleus, an mRNA strand is formed.
- Processing of the mRNA (eukaryotic)this is splicing
- Translation of the mRNA in a ribosome, a polypeptide chain is formed.
- Modification of the protein
Explain the process of ‘Transcription’ in protein synthesis
- Helicase breaks the hydrogen bonds in a specific region on DNA, separating the 2 strands, exposing the nucleotide bases, uncoiling.
- One of the DNA strands is used as a template (antisense strand) to make the mRNA molecule.
- Free nucleotides pair up with their complementary nucleotides on the strand, then RNA polymerase catalyses the formation of phosphodiester bonds.
- As RNA polymerase is adding nucleotides, the DNA strands start to rejoin behind it, and when RNA polymerase reaches the stop triplet code called the ‘terminator region’ it detaches. (only 12 bases are exposed at one time)
- In eukaryotic cells, the pre-mRNA is then spliced to form mRNA: the introns are removed, leaving a chain of exons. Now the mature mRNA can diffuse out of a nuclear pore and attaches to a ribosome in the cytoplasm.
Describe the process of ‘Translation’ in protein synthesis
- mRNA combines with ribosome in the cytoplasm, and tRNA attaches to amino acids within the cytoplasm.
- Each tRNA molecule has a sequence of 3 bases called an anticodon, where they have complementary base pairs on the mRNA molecule.
- tRNA molecules attach to the ribosome and their anticodon pairs up with the codons on the mRNA.
- A peptide bond joins the amino acids on the tRNA, and the tRNA molecules return back to the cytoplasm.
- The ribosome moves along there mRNA and the amino acids continues to join until a polypeptide chain is formed and it reaches a stop codon.
- Chain disassociates from ribosome.
What are ribosomes made from?
Ribosomal RNA and ribosomal protein.
Describe the structure of tRNA
-Has an amino acid attachment site
-Has an anticodon
-Made from around 80 nucleotides
-Single stranded
Define mutation
A change in the structure or amount of DNA.
What is gene/point mutation?
Change in the base sequence of a gene which can cause a change in the polypeptide chain. It is caused by errors that occur in our DNA replication.
What is chromosome mutation?
Change in the number or structure of the chromosomes. It is caused by errors that occur during cell division.
What are the 4 types of mutations?
-Substitutions
-Deletions
-Insertions
-Inversions
Some can be silent, some can cause frame shift (pushes the rest along).
Explain the ‘substitution’ mutation
One nucleotide in the DNA sequence is replaced by another.
It may not be harmful as the genetic code is degenerate, and the nucleotide that replaced it can still code for the same amino acid.
Explain the ‘deletion’ mutation
A nucleotide in the DNA sequence is lost.
This can be harmful as it causes a ‘frame shift’ which is where the code moves along one or back, causing all of the triplets to change, and different amino acids formed (wrong ones).
What is a frame shift?
When a mutation pushes the code along or back, changing the amino acids formed.
Define the term exons and introns
Exons are a base sequence coding for amino acids.
Introns are non-coding base sequences, only present in eukaryotic DNA
