Genetics 5.3 Flashcards
What is mRNA and what is it made from?
mRNA is a single polynucleotide strand. In mRNA groups of three adjacent bases are usually called codons. mRNA is made in the nucleus during transcription. It carries genetic code from the DNA in the nucleus, to the cytoplasm.
What is tRNA and what does it do?
It is a single polynucleotide strand that’s folded into a clover shape. Hydrogen bonds between specific base pairs hold the molecule in its shape. It is involved in translation, it carries the amino acids that are used to make proteins, to the ribosomes.
Which enzyme is used to break the hydrogen bonds between the Two nucleotide strands in DNA so that RNA can form mRNA?
RNA polymerase
What is pre-mRNA?
It is mRNA that still contains both introns and exons
When are introns removed?
Before the pre-mRNA leaves the nucleus, during splicing
How does RNA differ from DNA?
The sugar in RNA is a ribose sugar
The nucleotides form a single polynucleotide (in RNA)
Uracil (U) replaces thymine as a base (in RNA)
Outline transcription…
RNA polymerase attaches to DNA, (breaks hydrogen bonds) DNA uncoils at that point
One strand is then used as a template and RNA free nucleotides are made up to form a complementary strand
And mRNA strand is formed when RNA polymerase reaches a stop signal.
mRNA moves out of the nucleus through a nuclear pore.
Outline translation….
The mRNA attaches itself to a ribosome and a tRNA molecule, with an anticodon that’s complementary to the first codon on the mRNA attaches itself to the mRNA by specific base pairing, then a second and so on.
Each tRNA carries an amino acid, when the tRNA molecule leaves the mRNA it leaves the amino acid behind.
This creates a polypeptide chain.
Genetic code is non-overlapping, degenerate and universal, what does this mean?
Each base triplet is read in sequence, separate from the triple before or after. (Non-overlapping)
There are more possible combinations of triplets than there are amino acids. This means some amino acids are coded for by more than on base triplet (Degenerate)
Some specific base triplets code for the same amino acids in all living things (universal)
How to transcription factors affect the rate of transcription?
They move from the cytoplasm to the nucleus . They bind to specific DNA sites near the start of their target genes. They either increase or decrease the rate of transcription by either helping RNA polymerase bind or inhibiting it from binding.
Name a transcription factor and what it does….
An oestrogen receptor, which can bind to oestrogen forming an oestrogen-oestrogen complex. The complex can either act as an activator or as a repressor. Which it acts as depends on the type of cell. So the level of oestrogen in a particular cell affects the rate of transcription.
How can siRNA affect gene expression?
After transcription in the cytoplasm siRNA and associated proteins bind to the target mRNA. The proteins cut up the mRNA into sections so it can no longer be translated. So siRNA prevents expression of the specific gene as its protein can no longer be made.
How do mutagenic agents increase the rate of mutation?
Acting as a base- chemical base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA
Altering bases- some chemicals delete or alter bases
Changing the structure of DNA- some types of radiation can change the structure of DNA which causes problems in replication.
What are acquired mutations?
Mutations that occur in individual cells after fertilisation
What are the two types of gene that control cell division?
Tumour suppressor genes and proto-oncogenes
