BB1725 (Hetmanski) Flashcards
Definition of Cell
Smallest unit of a living organism
What are the different cell shapes
- Neurones
- Adipocytes
- Red Blood Cells
- Epithelial Cells
- Fibroblasts
Definition of Inheritance
Passing of physical or mental characteristics genetically from one generation to another
How does DNA become functional?
By being turned into proteins via RNA
Definition of Gene
Segment of DNA sequence that codes for one protein (1 RNA molecule)
What is the Genome?
All of the DNA in a cell (coding & non-coding)
Definition of Genetics
Study of Genes (and the genome)
Definition of Genomics
Study of Genome
Definition of Asexual Reproduction
Division of the cell to form two daughter cells, containing same genetic information as the mother cell
Definition of Sexual Reproduction
Fusion of two special cells (gametes) to form another type of cell (Zygote)
What is an Allele?
An alternative form of a gene
Describe DNA Structure
- Macromolecule (large molecule of atoms covalently bonded together)
- Two polynucleotide chains polymers (multiple units) of nucleotides
- Each chain is known as ‘DNA strand’
- Structure has major & minor groove
Key facts about DNA structure:
- DNA 2nm wide
- One full turn rises 3.4 nm
- There are 10 - 10.5 rises bases per turn
Why is DNA a helix and why is it a double helix?
To save space
For replication & stability
3 components of Nucleotides:
- Deoxyribose Sugar (backbone & stability) - strong covalent bonds
- Phosphate Group (Structure)
- Base (4 types - code)
Base + Ribose = Nucleoside
Base + Ribose + Phosphate = Nucleotide
What are Purines?
Double ring structures
- Adenine & Guanine
What are Pyrimidines?
Single ring structures
- Cytosine & Thymine
Describe Eukaryotic Packaging
Packaging of total cell DNA occurs in discrete units - “chromosomes”
In humans - 3.2x10ª chromosomes are divided between 46 chromosomes
Not all chromosomes are same size
Images of condensed chromosomes one called ‘karyotypes’
Describe Nucleosome
Functional unit of DNA packaging
8 Histone proteins:
- positively charged interact with negatively charged DNA
Core Histones of nucleosome are surrounded by 146 base pairs of DNA
DNA wraps 1.65x around histone core
Describe String of beads
Adjacent nucleosomes connect via spacer DNA (H1 HISTONE ATTACHES HERE)
Describe Chromatin Fibre
String of beads further coiled to form ‘Chromatin Fibre’
They stack together as a zig-zag
Role of Histone 1
Plays important role in stacking the two nucleosomes to form a chromatosome
How is DNA Packaged?
- Start with DNA
- DNA wraps around histones to form nucleoside
- Nucleosomes stack to form Chromatin
- Chromatin further packed by addition of scaffold proteins
How can DNA be accesses if tightly packed?
Via Scaffold proteins & loops
(Exact method is unknown)
What are the two types of chromatin & explain
Euchrommatin:
- Less condensed
- Does not strongly stain
- Major genes involved in transcription
Heterchromatin:
- Highly condensed chromatin visible by light microscopy in interphase eukaryotes
- Gene activity surpressed
Definition of DNA Replication
Copying of DNA that occurs during Mitosis and Meiosis
Definition of DNA Recombination
Exchange of Genetic Material
Helps drive evolution via meiosis
Can occur as part of DNA repair
What is the process of DNA Replication and explain it
Semi-conservative Replication
- Each daughter strand of new (replicated) DNA contains one strand from original strand and one new strand of DNA
DNA Replication Key Components:
- Four different Deoxynucleoside triphosphates
- DNA helicase - enzyme that unwinds DNA
- Single-stranded DNA binding proteins
- DNA Polymerase - makes the copy
- DNA Topoisomerase - helps with unwinding
- DNA Primase - helps with copying
- DNA Ligase - repairs DNA single strand nick
What are some problems that could occur during Replication?
- DNA Polymerase cannot start making a copy of DNA
- DNA Polymerase needs 3’ OH group to attach to the nucleoside triphosphate
- DNA Polymerase needs a primer
- Lagging strand can have a DNA Nick (But sealed by DNA Ligase)
What is the General Process of DNA Recombination?
- Enzymes generate double-strand DNA break and single stranded ends
- Single-strands find homologous DNA by DNA synapsis
- Synthesis of Heteroduplex region (Branch migration)
- Strand cutting to give two new molecules
When does DNA Recombination take place?
Takes place during:
- Meiosis
- Homologous Recombination Repair (HRR)
- Repair of double-strand break damaged DNA
What are the different types of Mutations?
- Deletions (loss of nucleotide(s))
- Insertions (gain of nucleotide(s))
- Substitutions (change of one base for another)
______________________________________________________ - Transitions: (Purine to Purine - A to G)
(Pyrimidine to Pyrimidine - C to T) - Transversions: (Purine to Pyrimidine)
Name the different Exogenous (External) Damage of mutations
Ionising Radiation (X-Rays)
- Single or double-strand breaks in DNA
UV (Sunlight)
- Thymine cross-linking
Chemicals
- Hydrocarbons in cigarette smoke
- Aflatoxins in mouldy peanuts
Name the different Endogenous (Internal) Damage of mutations
DNA Replication Errors
Hydrolysis - Spontaneous Depurination & Deamination
Oxidation
Define Depurination
Removal of Guanine or Adenine
Define Deamination
Conversion of cytosine to uracil
What are the consequences of DNA damage?
- Cell Death
- Functional decline of tissue
- Organ issue/failure (Neurodegeneration, kidney injury, cardiovascular disease)
- Cancer
- Developmental deficiencies
- Embryonic Lethality
Name the different DNA Repair Mechanisms and state the function
Direct Repair
- Reverses the DNA damage
Base Excision Repair (BER)
- Removes single damaged bases
- Single-strand break repair
- Main protector against metabolism damage
Nucleotide Excision Repair (NER)
- Removes Thymine dimers and large chemical adduct
Mismatch Repair (MMR)
- Removes mismatched base pairs and insertion/deletion loops
Non-homologous end joining (NHEJ)
- DS break repair
Homologous Recombination Repair (HR)
- DS break repair
What are the common themes of DNA Repair?
- Detect damage - proteins detect and bind
- Remove damage - nucleases
- Resynthesis/Repair - DNA polymerases and ligases
- Regulation - protein kinases
Definition of Transcription
Generates single-stranded RNA identical in sequence with one of the strands of the DNA duplex
Definition of Translation
Coverts the RNA sequence into amino acid sequence comprising a protein
Difference between RNA and DNA
RNA :
- Ribose sugar
- Uracil
DNA:
- Deoxyribose sugar
- Thymine
