DNA and Meiosis Flashcards
What is DNA made of?
NUCLEOTIDES
What do nucleotides contain?
a SUGAR (Deoxyribose), a PHOSPHATE and a BASE
DNA
A polynucleotide- made up of lots of nucleotides joined together.
What is the same/ different in every nucleotide?
Same sugar and phosphate, the base can vary.
What are the four bases?
A- adenine,T- thymine,C- cytosine,G- guanine
Structure of DNA
- DNA nucleotides join together to form polynucleotide strands.
- Nucleotides join up between the phosphate group of one nucleotide and the sugar of another, creating a SUGAR-PHOSPHATE BACKBONE.
- Two DNA polynucleotide strands join together by hydrogen bonds between the bases.
- Each base can only join with one particular partner- this is called SPECIFIC BASE PAIRING.
- Adenine pairs with Thymine, and Guanine with Cytosine.
- Two strands wind up to form the DNA double helix. Deoxyribose molecules alternates with phosphate to form the strands and the bases form rungs.
How is DNA adapted to carry out its functions? (6)
- Base pairs within helical cylinder so genetic info is somewhat protected from being corrupted by outside chemical and physical forces.
- DNA molecules v. long and are coiled very tightly, so lots of genetic info can fit into a small space in cell nucleus.
- Large molecule- hold lots of info
- Have a paired structure so makes it easier to replicate itself. SELF REPLICATION.
- Double helix makes it a v. stable cell and can pass from generation to generation without change.
- Two separate strands are joined only with H bonds, allows them to separate during DNA replication and protein synthesis.
What do the organic bases contain?
NITROGEN
What are the two types of base?
- Double ring structure (Adenine and Guanine) have longer molecules.
- Single ring structure (Thymine and Cytosine) have shorter molecules. Rungs of DNA made of one of each type.
How are the base pairs bonded?
Adenine and thymine- 2 hydrogen bonds
Cytosine and Guanine- 3 hydrogen bonds
They are COMPLEMENTARY to each other.
Eukaryotic DNA
LINEAR and associated with proteins.
- DNA molecules exist as chromosomes
- Really long DNA molecule, wound up to fit in nucleus
- DNA molecule wound around proteins which help support it
- The DNA is then coiled up very tightly to make a compact chromosome.
CHROMOSOME
A thread like structure made of protein and DNA by which hereditary information is physically passed from one generation to the next.
Prokaryotic DNA
- DNA shorter and circular
- Carried as chromosomes
- Isn’t wound by proteins
- it condenses to fit in the cell by supercoiling.
Chromosome structure
ONLY VISIBLE AS DISTINCT STRUCTURES WHEN A CELL IS DIVIDING.
- When visible they appear as two threads, joined at a single point. (centromere)
- DNA in chromosomes is held on position by proteins, highly coiled and folded.
- DNA- protein complex then coiled.
- Coil in turn is looped and further coiled before being packed into the chromosome.
A LOT OF DNA IS CONDENSED INTO A SINGLE CHROMOSOME.
HOMOLOGOUS CHROMOSOMES
a pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features. They are NOT necessarily identical, however, as individual ALLELES of the same GENE may vary e.g. one chromosome may carry allele for blue eyes, the other the allele for brown eyes. Capable of pairing during meiosis.
