Introduction to DNA Flashcards
How many chromosomes are there in each human cell?
46
Describe the relationship between DNA, Chromosomes and Genes
- Chromosomes are made of genes
- Genes are made of DNA
Describe DNA packaging (‘beads on a string’)
- DNA is wrapped around HISTONE cores forming a NUCLEOSOME
What is the name for a tightly packed sequence of nucleosomes?
Solenoid
What kind of chromatin has expressed genes and appears white on a slide?
Euchromatin
What form of chromatin has unexpressed genes and appears black on a slide?
Heterochromatin
What is a genome?
An entire DNA sequence of a species
What is the difference between the structure of a Nucleoside and a Nucleotide?
- Both have a base and a sugar
- A nucleotide also contains a phosphate group
Name two types of Nucleic Acids
DNA and RNA
Name the two types of Nitrogenous Base and how many carbon rings does each have?
Pyrimidine - 1 carbon ring
Purine - 2 carbon rings
Which two bases are Purines?
- Adenine
- Guanine
What are the 3 Pyrimidine bases?
- Cytosine
- Uracil
- Thymine
Which bases differ between RNA and DNA?
- Uracil in RNA
- Thymine in DNA
How are Nucleotides joined?
Phosphodiester bonds
What are the two chain ends of DNA strands?
5’P (phosphate group on 5th carbon in ring)
3’OH (OH group on 3rd carbon in ring)
What kind of bonds join DNA base pairs?
Hydrogen bonds
Which way are DNA ends written and read?
5’ to 3’
What is the function of DNA Polymerase in DNA replication?
- It catalysed the process
- It elongates each existing DNA strand by one nucleotide
What are the three stages of DNA replication?
- Initiation
- Elongation
- Termination
What happens in the Initiation phase of DNA replication?
- Helicase breaks the hydrogen bonds forming the Replication Fork
- Primase kick-starts the process
Which strand is coded continuously by DNA Polymerase and why?
- 3’ to 5’
- Anti-Parallel strand is being made (5’ to 3’)
Which strand is coded in bits and what are these bits called?
- Lagging strand
- Okazaki fragments
What chemical joins Okazaki fragments?
DNA ligase
What happens in the termination stage of DNA replication?
Two facing replication forks meet and DNA ligase joins the fragments
How many DNA molecules does a chromosome contain?
Can be one DNA molecule or two DNA molecules joined by a centromere
