nucleic acid structure and DNA replication Flashcards
two nucleic acids
-DNA
-RNA
bases in nucleic acids
purines: adenine and guanine
pyrimidines: Thymine (DNA) , cytosine and uracil (RNA)
what are genes
Genes are the units of inheritance
Genes have to be stable and repairable
Genes must be accurately copied between generations
Deoxyribonucleic acid (DNA) carries our genes
DNA carries the genes of all organisms, except some viruses
The structural and chemical characteristics of DNA make it a good gene carrier
nucleic acid strand
- DNA the polymer of nucleotides
-in living organisms its synthesised in the 5 to 3 direction
-phosphodiester bonds be the sugar phosphate backbone
dna structure
DNA is a double helix of anti-parallel strands held together by base pairing
how the structure of DNA makes it a good carrier of genetic information
STABLE AND STORES INFO WELL
The structure preserves the order of the four bases, encoding complex information.
This order of bases is called the sequence of DNA
Base-pairing allows the DNA to be copied accurately
DNA is a chemically relatively stable molecule
Because DNA is double stranded nature of DNA ensures that
damage to one strand can be repaired by copying the other.
Chromosomes
The DNA molecules in a cell are called chromosomes
Animals are diploid – they have two copies of each chromosome
All chromosomes have to be duplicated to make a new cell
The DNA in chromosomes is covered in proteins, this protein-DNA complex is called chromatin
why does DNA have to packaged in chromatin
DNA is very thin but the total length of DNA in a normal human cell is 2 metres.
This is packed into a nucleus with a diameter of 6-10 μm.
Any tangles would prevent replication and use of genes
Each gene has to remain accessible for use
Tension can break the DNA
Systematic and safe storage is very important!
nucleosome
-this is the basic unit of chromatin (nucleosomes make chromatin)
-DNA wrapped around proteins
-electrostatic interaction forms this
DNA polymerases
(enzyme)
-repair and replicate DNA
-only add nucleotides to the 3’ end of an existing strand, meaning that DNA synthesis always occurs in the 5’ to 3’ direction
-primer is a short segment of either RNA or DNA that provides a 3’ hydroxyl group (-OH) to which DNA polymerase can add new nucleotides. (can be DNA or RNA) (natural there in DNA repair)
DNA replication
- Breaking the base pairing and unwinding the double strand using DNA helicase
- primase adds a short RNA primer to provide a starting point for DNA polymerase. uses RNA polymerase generates a short piece of based pairs RNA as it doesn’t need a 3 end to start from mirrors the 3’ prime end in DNA repair
- now DNA polymerase adds new nucleotides to the 3’ end of the primer, synthesizing a new strand in the 5’ to 3’ direction.
but now you have a DNA RNA hybrid
- Once the entire DNA molecule is copied, the RNA primers are removed and replaced with DNA.
The two new DNA strands are proofread for errors, ensuring accurate replication.
Telomeres
The telomeres are special regions at the ends of chromosomes that protect them from deterioration or from being mistakenly repaired as breaks. They ensure that the chromosome ends are not lost during DNA replication. divide more times cause ends won’t be lost
pre mitosis facts
-The duplicated chromatin is packed tightly, shortening the length of the chromosome and reducing the chances of tangles or breaks
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After DNA replication, the duplicated chromosomes stay attached to each other at a single point
called centromere
Anti-microbial drug targets in DNA synthesis
Many antibiotic and antiviral drugs inhibit the DNA metabolism of the microbe/virus, but not of the host
