DNA & Meiosis Flashcards
What three components make up a nucleotide?
- deoxyribose (sugar)
- a phosphate
- a base (either single ringed: C & T, or double ringed: A & G)
Why type of reaction forms a nucleotide?
Condensation
What are the pairs of bases?
Adenine two H+ bonds Thymine
Guanine three H+ bonds Cytosine
Why are the quantities of A&T and G&C always the same?
Because they are bonded in complementary pairs
What other element is in the base group of a nucleotide?
Nitrogen
What are the uprights & rungs of the DNA ladder made from?
Rungs = pairs of bases Uprights = deoxyribose-phosphate molecules
How are polynucleotides formed?
- condensation reaction between deoxyribose sugar & phosphate between two different nucleotides
- water lost = phosphodiester bond formed
What is the name of the structure of DNA?
Double-helix structure
How do different DNA molecules differ from one another if there is always a deoxyribose sugar, phosphate & the 4 bases in each one?
Different proportions of bases ( ratio between pairs varies from species to species)
Different sequence of bases
How is the DNA molecule adapted to carry out its functions?
- stable: pass through generations without change
- two polynucleotide chains are joined by H+ bonds = separate in DNA replication
- large molecule = carries a lot of genetic info
- base pairs protected within helical structure from outside chemicals
How many bases make up an amino acid?
Three base pairs - triplet code
How are different amino acids made?
Different combination & sequence of bases
What is a gene?
Genes are sections of DNA and are found on chromosomes. They code for proteins (polypeptides) as the contain the instructions (specific base sequences) to make them
What is an intron and exon?
Intron: Section of non-coding DNA that can occur within genes as multiple repeats, are removed in protein synthesis
Exon: opposite
Give three features of the triplet code
- the code is non-overlapping
- it’s a Degenerate Code, because most amino acids have more than one triplet code
- three triplet codes don’t code for any amino acid: Stop Codes mark the end of a polypeptide chain
Besides introns what is another region in genes that don’t code for amino acids?
Multiple repeat regions (DNA sequences that repeat over and over)
What’s the difference between prokaryotic & eukaryotic DNA?
- prokaryotic = DNA plasmids (rings)
- eukaryotic = linear DNA (form chromosomes)
What a phenotype?
The characteristic produced by a gene
What is a genotype?
A type of gene (codes for the phenotype)
What is the sequence that shows how genes determine our phenotype?
- DNA sequence determines amino acid sequence
- Protein/ enzyme formed
- Enzymes control metabolic pathways
- Metabolic pathways help determine nature & development
What is an allele?
A form of a gene, different alleles code for slightly different versions of the same characteristic
How many pairs of chromosomes do humans have?
23 pairs
What is the name of a single thread of a chromosome?
Chromatid
What are pairs of matching chromosomes called?
Homologous pairs
What makes two chromatids a homologous pair?
- same genes (but different alleles)
- same size
How many molecules of DNA is in one chromatid?
Only one - but the DNA molecule is extremely long
What joins two chromatids together to form a chromosome?
The centromere
What is the diploid number of chromosomes in a human cell?
46
What would happen if there was a mutation affecting the sequence of bases in a gene that codes for an enzyme?
- may not fold up properly = wrong active site shape
What is the name given to the position on a chromosome that a particular allele occupies?
The locus
How are new alleles of a gene produced?
Mutations
How can mutations affect enzyme activity?
They prevent it from forming it’s correct shape
What is meant by semi-conservative replication
Producing two copies of DNA, that each contained one of the original strands and one new strand
What does meiosis do?
Produces gametes / 4 non-identical daughter cells
Does meiosis produce diploid or haploid daughter cells - and why?
Haploid - so that when gametes fuse there is not too much DNA
What are the 4 stages of Meiosis One (the first division)?
- prophase I: nuclear membrane disappears, spindle fibers, centrioles move to opposite poles, chiasmata form
- metaphase I: chromosomes line up in their homo pairs along equator, independent assortment occurs
- anaphase I: spindle fibers contract pulling chromosomes to opposite poles
- telophase I: cell splits = two haploid cells produced
What are the 3 stages of Meiosis Two (second division)?
- metaphase II: chromosomes line up on equator
- anaphase II: spindle fibers contract & pull chromatids (half of chromosomes) to opposite poles, both cells split
- telophase II: 4 unique haploid cells produced (¼ mass of original DNA)
What happens when the chiasmata form in Prophase I?
Chromatids wrap around each other & exchange genetic info
What is independent assortment?
Chromosomes line up along equator in random order
What is stop/start codon?
There are only 3 combinations in the work of 3 base pairs, ATT, GCC, TGC, (triplet codes) that do not code for any amino acid, and so act as the full stop between different amino acids.
What are two ways in which genetic variation is created through meiosis?
- independent assortment
- chiasmata cross over
What is a nucleotide?
A form basis of DNA that join together
