Classic ( Mendelian ) genetics Flashcards
What is our genetic information stored in
Chromosomes which are composed of DNA
How does DNA exist
As two complimentary chains of nucleotides
In the nucleus in the form of a double helix
What does a nucleotide contain?
Identical pentose sugar ( deoxyribose or ribose )
Phosphate group
Base- C,G,A,T ( 4 different bases in DNA )
How are the chains joined together?
Adjacent/ complementary base pairs are joined by hydrogen bonds.
Pentose sugar and phosphate make up of backbone of DNA
2 chains of DNA are mirror images
Bases stick out of backbone
What is a gene
- A piece of DNA that codes for the production of a particular protein
- Series of nucleotides
How do bases code for amino acids
Each triplet codon codes for one amino acid
Coded for by a triplet codon consisting of 3 adjacent nucleotides.
What is DNA in humans split into
46 chromosomes occuring as 23 homologous pairs
Each chromosome is a chain of genes
-There are 22 pairs of autosomes and one pair of sex chromosomes - during mitosis 1 member of homologous pairs from mother and 1 from father
What happens in protein synthesis?
Transcription- transfer the triplet codons (copied) on DNA to mRNA
mRNA - leaves nucleus
mRNA binds to ribosomes and combines with complimentary tRNA molecules (translation)/
The amino acids on adjacent tRNA molecules join to form a protein- with peptide bonds.
Makes growing chain of amino acids
Protein synthesises in cytoplasm on ribosome
Where is DNA - what is its structure
DNA lies within the nucleus and is closely associated with histone proteins which are important for regulating expression of particular genes
Normally it is in fairly loose agregations and strands in the nucleus. But during mitosis it condenses
What is the format of most of DNA
Most of DNA does not code for proteins - this junk DNA is known as introns
97% of our DNA is introns
What is coding region of DNA
Exons (3% codes proteins)
How many genes do we have in total?
- 30,000
* ( same as cabbage - difference is the number of introns )
Why do we need introns
- Help in expression of certain genes
- They make you, you
- During evolution, sequence of bases in introns is conserved = over millions of years it doesnt change
- If it was truly junk DNA with no purpose, random mutations would accumulate and introns would change over time - they dont - which means they are positively selected for
How many genes do we have for most traits
2
Where are the genes for traits located?
At the same locus on homologous chromosomes
What are 2 copies of the same gene?
Homozygous alleles
e.g. both genes code for blue eyes
What are 2 copies of different genes?
Heterozygous alleles
e.g. one codes for the blue eyes and one codes for brown eyes
What are the 2 genes
Alleles
2 genes for each trait
What is genotype
A persons genetic makeup
Full complementary genes - identity of all genes
What is phenotype
The expression of this genotype - physical us
What is life span of most cells and what does that mean
Limited life span
e.g. red blood cells = 120 days
That means they need to be replaced by cell divison
Wha are the cell types which do not get replaced?
CNS neurons
Cardiac muscle - in heart
Corneal endothelial cells
How do most cells replicate?
By division
What happens when a parent cell divides?
It must pass on all its DNA to the 2 daughter cells
This is achieved by the process of MITOSIS
What is mitosis?
Division of nucleus through cell division - makes sure each cell gets full complement of DNA - all the genes - 46 chromosomes get passed onto offspring
What does cell cycle show
That life of a cell can be divided into various phases
What are the 2 phases of the cell cycle
Interphase - 4 stages
Mitotic phase - mitossi and cytokinesis
What happens in G0
Normal cell metabolism occurs - duration is variable
When most cells get ready for division they go from G0 to G1
What is G1?
- Organelles are duplicated e.g. number of mitochondria increases, ribosomes, centrioles double/replicate
- Prepares cell for replication by the multiplication of organelles
- Cell growth
- Protein synthesis
- Cell gets ready to divide
What are the 4 phases of interphase 1
- G0
- G1
- S phase
- G2
How many centrioles does cell normally have
1 but in preparing for cell division in G1, number of centrioles doubles
What happens during the S phase
- DNA replicates = to make 2 identical strands of DNA
-DNA polymerase binds onto DNA and unzips it into 2 complementary chains - 2 strands of DNA unwind
-DNA polymerase moves along the exposed chains adding complimentary nucleotides from a pool within the nuceloplasm. e.g. if its A, it adds T = 2nd complementary chain of DNA
Forms 2 identical strands of DNA (4 strands)
What happens during G2
Proteins needed for cell division are synthesised = protein synthesis
The cell is now ready for division.
Replication of the cytoplasm = cytokinesis
Division of the nucleus= MITOSIS
How does DNA change after S phase
DNA originally consists of 2 strands of nucleotides - now consists of 4 strands of nucleotides - 2 identical copes of DNA -
What is the M phase
Division of the cell/nucleus
What is interphase
Cell gets ready and everything replicates
What is early Prophase
- DNA condenses to form bar like chromosomes
-Each chromosome have 2 copies of DNA - Each copy of DNA/ chain of DNA of chromosome is known as a chromatid
- 2 chromatids of each chromosome are joined by a centrosome
-Nuclear membrane disintegrate
-Nucleolus breaks down
-2 centrioles move to opposite ends/poles of cells
-Secrete microtubules- mitotic spindle
= PROPHASE IS BIGGEST PHASE OF MITOSIS
What is the 1st phase of the division of the nucleus
Prophase
What happens during late prophase
Chromosome attach to mitotic spindle
What happens in metaphase?
- Spindle fibres form
- Chromosomes arrange themselves along the equator/ centre of the cell