1.1 DNA and the genome Flashcards
What is DNA?
Genetic material that is inherited (passed down from generation to generation) which can be located within the nucleus of all cells {apart from red blood cells.}
Why is DNA important?
DNA is a long chemical sequence containing the info for that living thing to develop, survive and pass on its genetic info to the next generation
What is a genotype?
The DNA chemical sequence differs between individuals. The pattern of this sequence is called its genotype.
What is a genome?
The sum total of all genetic info of an individual is the genome.
Function of DNA?
DNA contains genetic info to make the specific proteins required by a cell
The proteins determine a cell’s structure allowing it to perform it’s function - allowing the cells to differentiate
Copies of the cells genetic info are passed onto the daughters cells during cell division (mitosis)
Copies of the cells genetic info are passed onto the next generation when gametes fuse during fertilisation - the genetic code is inherited
How does DNA package in Human chromosomes?
- DNA double helix is wrapped around histone proteins forming nucleosomes
- The chain of nucleosomes then folds into a thicker chromatin fibre
- The thick chromatin fibre then folds again, on a non histone protein scaffold to form looped fibres
- the folded chromatin then folds further to produce a condensed chromosome
What do proteins contain?
the elements carbon, hydrogen, oxygen and nitrogen
What are proteins?
Proteins are large insoluble molecules made up of a chain of smaller molecules called amino acids of which there are 20 types
What are structural proteins?
Building proteins forming hair and cell membranes
What are enzymes?
Speed up the rate of reactions such as photosynthesis and respiration that are essential for life
What are hormones?
Chemical messengers e.g. insulin
What are antibodies?
defence against antigens
What is the shape of DNA?
DNA has two strands coiled into a double helix.
Each strand of DNA is made up of nucleotides
What is a nucleotide?
A nucleotide consists of a phosphate group, a deoxyribose sugar and a nitrogenous base
How is the carbons on the deoxyribose sugars numbered?
C1 is on the right and the carbons are numbered in a clockwise direction
C5 is situated between C4 and the phosphate
How does it form a strand?
Nucleotides are linked by their deoxyribose sugars and phosphates to form a strand with a sugar phosphate back bone.
Strong chemical bond link nucleotides in one strand.
* free nucleotides can join onto DNA at 3’ end only *
What is the complementary base pairing rule?
adenine and thymine
guanine and cytosine
What direction do the strands run in?
The two DNA strands connect running in opposite directions.
The strands are said to be anti parallel
One strand runs 3’ - 5’ the other 3’ - 5’
Features to remember of a DNA molecule for the exam?
- double helix shape
- Sugar phosphate backbone
- Anti parallel strands
- Hydrogen bonds linking strands
- complementary base pairing rules applied to nucleotide
Organisms fall into what two categories?
Prokaryotes and Eukaryotes
Prokaryotes Vs Eukaryotes
in both prokaryotic and eukaryotic cells, DNA is organised into structures called chromosomes In prokaryotes (bacteria) chromosomes are circular In eukaryotes (animals and plants) chromosomes are linear
What is a prokaryotic cell?
A prokaryotic cell does not have a membrane bound nucleus
DNA is found in the cytoplasm in the form of a large circular chromosome or smaller rings called plasmids
Prokaryotic cells also do not have a membrane bound organelles (chloroplasts or mitochondria)
How is bacterial plasmids used in genetic engineering?
They are extracted from the bacteria, cut open with endonucleas enzyme leaving sticky ends
A gene from another organism is placed between the sticky ends and the plasmid is sealed with the ligase enzyme
the bacterial cell now has a gene that can code for a foreign protein
What is a eukaryotic cell?
they have a membrane bound organelle and organelles
Features of Prokaryotes
dna packaged into chromosomes
dna not found within a nucleus
plasmids can be present
dna usually found as a double stranded circular molecule
dna is the genetic material
dna is double stranded
organisms have a different sequence of bases along dna
Features of Eukaryotes
Genetic material contained within the nucleus
dna packaged into a set of linear chromosomes
chloroplasts dna in some species
dna can be a mix of circular and linear chromosomes
mitochondrial dna located within the cytoplasm
dna is the genetic material
dna is double stranded
organisms have different sequence of bases along dna
When do chromosomes condense?
they condense in eukaryotic cells during mitosis when they become visible with a microscope
Because the dna molecule is very long, what must it do?
coil around bundles of histone proteins to form chromatin fibres, which loop, fold and condense to form chromosomes
where are mitochondria found?
in the cytoplasm of cells including ova
where is mitochondrial dna inherited exclusively from?
our mother
what do mitochondria genes code for?
enzymes of aerobic respiration so mutations can be lethal
What are yeast cells?
eukaryotic, unicellular fungi
What do yeast cells contain?
linear chromosomes within a membrane bound nucleus.
they also contain some circular plasmids in their similar to those found in prokaryotes
which of the following are eukaryotes or prokaryotes bacteria yeast cell palisade mesophyll cell cheek cell?
bacteria - prokaryote
the rest are eukaryotes
which of the following have a nucleus present bacteria yeast cell palisade mesophyll cell cheek cell?
yeast
palisade mesophyll cell
cheek cell
which of the following have a chloroplast present bacteria yeast cell palisade mesophyll cell cheek cell?
palisade mesophyll cell
which of the following have a plasmid present bacteria yeast cell palisade mesophyll cell cheek cell?
bacteria AND yeast
which of the following have a mitochondria present bacteria yeast cell palisade mesophyll cell cheek cell?
yeast
palisade mesophyll cell
cheek cell
Why are yeast cells unusual in the organism of DNA?
They contain plasmids but have a nucleus with linear chromosomes and nuclear bound organelles in their cytoplasm
What is a DNA fingerprint or profile?
the unique pattern of fragments a persons DNA base sequence produces when their DNA is ‘digested’ with restriction endonuclease (enzymes)
What is gel electrophoresis?
DNA profiling makes use of the technique gel electrophoresis where the fragments of DNA in a sample can be separated by size on the …. of an electrical voltage
Describe the gel in gel electrophoresis and the effect it ahs on the size of molecules?
the gel is porous and small molecules move faster through the gels than larger molecules and so travel further in …. time
molecules of the same size travel the same distance and, when strained form a bond on the gel
