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)
What is DNA ligase?
Joins nucleotides together by catalysing the formation of phosphodiester bonds
What are okazaki fragments?
Newly synthesised DNA fragments formed on lagging parent strand during DNA replication
What is epigenetics?
Study of changes in organisms caused by modification of gene expression as opposed to alteration to genetic code itself
