2.1, 2.2 Introduction To DNA and precision med Flashcards
What is a DNA molecule and its function? (3)
- Deoxyribonucleic acid
- Double helix
- Contains genes - Length of DNA that codes for a protein
How is DNA packaged to form a chromosome?
- DNA wrapped around a histone forming ‘beads on a string’
- Further compressed into a solenoid
- Further folds to form our chromosome
What is a piece of DNA wrapped around a singular histone called?
A nucleosome
What is chromatin?
DNA + histone proteins
Describe the structure, function and colour on microscopy of heterochromatin (2)
- Solenoid form of DNA and histones
- Genes are not expressed
- Darker
Describe the structure, function and colour on microscopy of euchromatin (2)
- Beads on a string
- Genes are expressed
- Lighter
What are genes?
- Distinct sequence of nucleotides that carry a code for proteins
What is the human genome?
Entire DNA sequence in humans i.e. Humans - 23 pairs of chromosomes
What are autosomes and how many do we have? (2)
- Chromosomes that contain genes that relate to anything but sex determination
- We have 22 autosomal pairs (i.e. 44) and 1 pair of sex chromosomes (i.e 2)
Name and describe the structure of the two pentose sugars that can be found within our bodies. Where are these located?
- Ribose - pentose sugar with OH group on 2nd Carbon within ring - located in RNA
- Deoxyribose - pentose sugar with H group on 2nd carbon within ring - located in DNA
What is the difference between a nucleotide and nucleoside?
Nucleotide - phosphate + sugar + base
Nucleoside - sugar + base
What are the two types of nitrogenous bases, name the base pairs that associate with them and how many rings each base has.
- Purines - Adenine, Guanine - 2 rings
2. Pyramidines - Thymine, Cytosine, Uracil - 1 ring
How many hydrogen bonds do the base pairs A and T and G and C make?
A and T - 2
G and C - 3
Describe the two DNA strands that bond together forming our DNA molecule.
- DNA strands are COMPLEMENTARY
- run ANTI-PARALLEL to each other
- By convention, top strand always written 5’ to 3’
What bonds join nucleotides to each other forming the DNA strands? What parts of the nucleotide make this bond? (2)
- Phosphodiester bonds
- 3’ Carbon to the oxygen to the Phosphate
- Distinct ends, 5’ Phosohate and 3’ OH
Where does DNA replication occur within a cycle of mitosis?
Within the S phase
What is the term describing the DNA replication process and the fact that each new molecules has 1 recycled strand?
Semi-conservative
Describe the DNA replication process in eukaryotes
- Initiation
- DNA helicase unwinds DNA at origin of rep
- single strand binding proteins keep strand separated
- DNA primase kick starts addition of nucleotides by adding short sequences of RNA called primers - Elongation
- leading strand - DNA polymerase takes over and elongates
- lagging strand - okazaki fragments formed as DNA polymerase works in 5’ to 3’ direction continuously only on 3’ to 5’ strand.
- Exo/endonuclease proof reads replication
- polymerase reverses and corrects
- DNA ligand seals okazaki fragments into one continuous strand
- Termination
- two facing replication forks meet and DNA ligase joins final fragments
Name a difference in prokaryotic and eukaryotic DNA rep
Eu - many origins of replication
Pro - 1 origin of replication
Describe the DNA replication process in prokaryotes
- Recognition of origin of replication
- Primase
- DNA polymerase + other specific proteins
What drives the addition of nucleotides onto elongating strand?
Loss of pyrophosphate (PPi)
One DNA molecule is called a chromosome, what are the two DNA molecules after replication called?
A chromosome too! Have sister chromatids which are identical.
Briefly describe precision medicine
Moving from one-size-fits-all medicine to tailored therapy.
Involves pharmacogenetics - Study of how a persons genes affect their response to a drug
What are immunotherapeutic checkpoint inhibitors?
Immune checkpoint inhibitors unleash a patients own T cells to kill tumours (e.g. For cancer)
