storing and using genetic information Flashcards
define phenotype
outward, physical manifestation of organism
define genotype
full heredity information of an organism
what is protein structure ultimately dependent on
the primary structure of amino acids
dna is a chain of …
nucleotide monomers
what are the complementary base pairs
A-T/U
C-G
what are some of the functions of the nucleus
- usually the largest organelle in the cell
- contain most of the cell’s genetic material
- replication of DNA and transcription occur here
how is DNA packaged in the nucleus
packaged into chromosomes in a highly orderred manner
define chromatin
the mixture of DNA, RNA and proteins that package DNA within the nu
can be heterochromatin or euchromatin
how is chromatin made more accessible for transcription and replication
○ Histones can be enzymatically modified
- Histones can be displaced by chromatin remodelling complexes (no longer associated with histones)
- these processes are reversible
define semi-conservative replication
one half of each new molecule of DNA is old, one half new
explain bi-directional dna replication
- Replicated in the 5’ to 3’ direction
DNA polymerase can only add new nucleotides to the 3’ end of the growing strand.
Okazaki fragments are formed on the lagging strand which are joined together by DNA ligase to form one continuous strand. However the 5’ end of the lagging strand cannot be replicated in this way so a specialized enzyme – telomerase – replicates the 5’ ends of the lagging strand.
how is DNA packaged during metaphase
- DNA is packed about 10 000 times more tightly in metaphase than in cells in other states - chromosomes are most compacted and visible during metaphase
- this allows an ordered 50:50 split when the chromosomes separate to allow normal functioning
- Achieved by repeatedly folding chromatin fibres into a hierarchy of multiple loops and coils
what proportion of the genome is coding DNA
<2% repeated sequences (Junk DNA) that are non-coding make up at least 50% of the human genome and it s important in regulating gene expression
genetic code
describes how base sequences are coded into aa
codon
set of 3 bases, codes for a particular aa
describe the degenerate nature of the genetic code
there are 64 possible codons but only 20 aa
With the exception of methionine and tryptophan they are all encoded by more than one codon, this is referred to as degeneracy or the redundancy of the genetic code.
Codons which refer to the same amino acid are called synonyms and tend to be very similar. Variations between synonyms tend to occur at the third base of the codon – the wobble position.
how does degeneracy minimise the effect of genetic mutation
alterations to the base sequences are less likely to alter the protein being coded for. This prevents any alteration in protein structure and hence function
what is the function of RNA
participates in protein synthesis
what is alternative splicing
process by which the exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing.
The resulting different mRNAs may be translated into different protein isoforms; thus, a single gene may code for multiple proteins.
Alternative splicing occurs as a normal phenomenon in eukaryotes, where it greatly increases the diversity of proteins that can be encoded by the genome
reading frames
- Initiation codon determines the reading frame of the RNA sequence
- Usually only one reading frame contains useful information with others including a number of stop codons which will prevent the wrong protein being synthesised.
- A set of codons runs continuously and is bounded by a start/initiation codon and a termination codon – this is known as the open reading frame and is used to identify DNA which encodes protein sequences in genome sequencing projects.
tRNA
- Major role is to translate mRNA sequence into aa sequence
Acts as an adaptor molecule between the coded aa and the mRNA
rRNA
- Component of ribosomes
- rRNA molecules are produced in the nu
- Transported to cytoplasm, combine with proteins to form a ribosome
Several ribosomes can translate mRNA at one time creating a polysome
