genetics + genetic disorders Flashcards
what is the phenotype?
outward, physical manifestation of organism
what is the genotype?
full hereditary information of organism, although not all of the information may be expressed
a DNA nucleotide contains (3)
deoxyribose sugar, a base (T, G, A or C) and a phosphate group
describe the structure of a DNA molecule
- double helix
- strands run antiparallel (that is one runs 5’ to 3’ from the top of the helix in the picture, while the other runs 3’ to 5’.)
- sugar phosphate backbone
- right handed
what are the complimentary base pairs
adenine always pairs with thymine (t replaced with uracil in RNA molecules) (A-T/U)
-cytosine pairs with guanine (C-G)
describe the structure of the nucleus
- contains most of the DNA within the cell
- site of DNA replication + transcription for protein synthesis
describe a chromosome
- the structure that a single piece of DNA molecule is packaged into in the nucleus
- has shorter p arms, a centromere and longer q arms
- humans have 46
what is chromatin, and what two forms can it take?
- chromatin is the name of the mixture of DNA, proteins and RNA that package DNA within the nucleus
- heterochromatin is the condensed form
- euchromatin is the extended/loose and more functional form
describe the structures of transcription/replication
-both require 2 separate strands of DNA so that enzymes can access the DNA template
-cells must have means of opening up chromatin fibres and/or removing histones for access
= histones can be enzymatically modified or can be displaced by chromatin remodelling complexes (both reversible)
describe the process of DNA replication
-a semiconservative process
-DNA molecule ‘unzips’ by breaking hydrogen bonds
-new nucleotides are then paired with the two strands so one strand is old and one new
-replicated in the 5’ to 3’ direction; nucleotides added by DNA polymerase (3’ end of strand)
-okazaki fragments are formed on the lagging strong which are joined together by DNA ligase to form one continuous strand
at 5’ end, telomerase replicates these ends of the lagging strand
during which mitotic phase are chromosomes most compacted and visible?
metaphase, where DNA is packed about 10,000 tighter than in cells of other states
describe the function and purpose of exons and introns
- exons are coding regions of DNA
- introns are non-coding regions
- during transcription, introns are spliced out and axons form mRNA
describe a codon
- a set of 3 bases
- each codon specifies a particular amino acid
describe degeneracy/redundancy of the genetic code
- no. of codons > no. of amino acids
- all amino acids but 2 are coded for by more than one codon
- codons which refer to the same amino acid are called synonyms and tend to be very similar.
what is the role of RNA?
-to participate in protein synthesis (mRNA)
describe the function of mRNA
- like all DNA it is (obviously) transcribed from DNA
- it carries information required for protein synthesis
what does the process of alternative splicing entail?
Alternative splicing is a process by which the exons of the RNA produced by transcription of a gene (a primary gene transcript or pre-mRNA) are reconnected in multiple ways during RNA splicing. The resulting different mRNAs may be translated into different protein isoforms; thus, a single gene may code for multiple proteins.
describe the function of tRNA
- major role is to translate mRNA sequence into amino acid sequence.
- acts as an adapter molecule between the coded amino acid and the mRNA
describe the function of rRNA
- it is a component of ribosomes
- rRNA molecules are produced in the nucleus then transported to the cytoplasm to combine with proteins to form a ribosome
how is a polysome created?
several ribosomes can translate mRNA at one time creating what is known as a polysome
describe the structure of a eukaryotic chromosome
- linear
- telomeres at tips
- centromere
- hetero and euchromatin regions
in a telomere, what are okazaki fragments?
- okazaki fragments are short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication. They are complementary to the lagging template strand, together forming short double-stranded DNA sections.
- each okazaki fragment has to be initiated by an RNA primer that will be removed from the fragment before it gets ligated to the next piece of DNA
what are the stages of the cell cycle?
- interphase (G1, growth; S, DNA replication; G2, further growth and preparing to divide)
- mitosis (propase, metaphase, anaphase, telophase)
describe prophase
- chromosomes condense
- nuclear membrane dissolves
- spindle fibres form from the centriole