Storing and using genetic info Flashcards
describe the double-helical structure of DNA
DNA is a chain of nucleotide monomers, each containing a sugar, base and phosphate group. The bases are stacked up, bound on the outside by the sugar-phosphate backbone. The two chains run anti-parallel to one another
one runs 3’ to 5’ and the other 5’ to 3’
Describe how DNA forms chromosomes
DNA winds around histones
How is DNA replicated?
special proteins (DNA helicase) 'unzip' the double helix by breaking the H bonds DNA polymerase can only add new nucleotides to the 3' end of the growing strands. Fragments are formed on the lagging strand which are joined together by DNA ligase to form one continuous strand. Howevere, the 5' end of the lagging strand cannot be replicated in this way so a special enzyme 'telomerase' replicates the 5' ends of the lagging strand.
Complementary base pairing
A-T
G-C
structure of the nucleus
- contains most of the cell’s genetic material (DNA)
- DNA replication and first step of decoding it for protein take place here
what does telomerase do?
replicates the 5’ ends of the lagging strand
How is a base sequence of DNA transcribed into a base sequence of RNA
In the genome, each set of 3 bases is called a Codon. initiation codon (only has one possible codon sequence) tells enzymes where to begin the transcription of RNA -from there, sequence is read in Codons until the Termination Codon is reached, which tells the enzymes to stop transcribing -Splicing of introns occurs leaving exons and produces a strand of mRNA at end- cap is added to 5' end and 3' end to protect it from being broken down by other enzymes
Genotype
all the hereditory info of organism (even if it isn’t switched on or expressed)
Major groove
most of the interactions with different molecules happen here i.e Transcription factor proteins
Minor groove
too narrow for anything to fit in i.e proteins
How is the physical shape of DNA molecule affected if base pairing is incorrect?
ie if A-C or G-T instead of A-T and G-C
as when bases pair correctly they fill a particular space, two sets of comp bases fit together well and enables DNA molecule to be packed tightly
hydrogen bonds are easily…
broken down so can zip and unzip strands easily for DNA replication
where is genetic material held?
most is in the nuclei but the rest is in the mitochondria as it has it’s own genome
what is the nucleolus involved with?
making ribosomal RNA
this is important as if you didn’t make this then you wouldn’t have a fully functioning ribosome and so you couldn’t make protein
Two reasons for highly ordered structure in chromosome?
- To pack everything in
- To allow regulation (by histones)
Genetic testing:- banding pattern
dark banded patches- condensed parts of chromosome. Heterochromatin- less active, switched off, no gene expression produced
light patches- euchromatic-more active
how are histones involved in regulating gene expression?
regulate the structure and function of nucleosomes
- Anything that makes nucleosomes more difficult to move will repress transcription, and ultimately down regulate the expression of the associated gene.
DNA replication is described to be
semi-conservative- one half of each new molecule of DNA is old, one half is new
bi-directional- 5’ to 3’ direction, continuous and lagging strand however
RNA splicing
removes non-coding regions of DNA (introns)
leaving only exons which go on to make protein
What is a gene?
All the info that a cell needs to make a particular protein is contained in a sequence of DNA known as a gene.
-huge amount of variation can be produced
-each set of 3 bases is called a codon
each codon specifies a particular amino acid- only 20 amino acids though so more than one codon can refer to one amino acid
Role of RNA
main role is to participate in protein synthesis
mRNA
transcribed from DNA
carries info for protein synthesis
alternative splicing
the exons of the RNA produced by transcription of a gene are reconnected in multiple ways during RNA splicing.
Methionine
only has one possible codon sequence so acts as the initiation codon and tells enzymes where to begin with the transcription of RNA
Sequence is read in…
codons until the termination codon is reached, which tells enzymes to stop transcribing. Once this has occurred RNA splicing happens producing a stand of mRNA
what happens once mRNA has been produced?
a cap is added to the 5’ end and a tail is added to the 3’ end to protect it from being broken down by other enzymes
