Human Cells: Structure and Replication of DNA
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Genetic information is what?
Inherited
DNA is a substance that does what?
Encodes the genetic information of heredity in a chemical language
What is DNA?
A very long double-stranded molecule in the shape of a double helix
Each strand of DNA is made up of what?
Chemical units called nucleotides
A nucleotide is made up of what?
A deoxyribose sugar, a phosphate and a base
Deoxyribose molecules have how many Carbon atoms?
Five Carbon atoms and are numbered 1 to 5
The phosphate of one nucleotide is joined to what Carbon and linked to what other Carbon of the next nucleotide in the strand to form what?
Joined to Carbon 5 Linked to Carbon 3 To form 3-5 sugar-phosphate backbone
What are the four different DNA bases called?
Adenine (A), Cytosine (C), Guanine (G) and Thymine (T)
The nucleotides of one strand of DNA are linked to the nucleotides on the second strand through what?
Their bases - the bases form pairs that join the strands
Bases pair in a complementary way, what are the complementary pairs?
Adenine pairs with Thymine Guanine pairs with Cytosine
Base pairs are held together by what?
Weak hydrogen bonds
What is on each end of the sugar-phosphate backbone?
The 3’ end starts with a deoxyribose molecule and the 5’ end finishes with a phosphate
The two strands of a DNA molecule run in opposite directions and are said to be what?
Antiparallel to each other
The base sequence of DNA forms what?
The genetic code
DNA molecules replicate before what?
Cell division
What is replication?
The process by which DNA molecules can direct the synthesis of identical copies of themselves
DNA replication requires what?
The original DNA strands to act as template strands, a supply of DNA nucleotides, the enzymes DNA polymerase and ligase, and ATP
What happens prior to cell division?
DNA is replicated by the enzyme DNA polymerase
DNA polymerase needs what to start replication?
Primers
What is a primer?
A short complementary strand of nucleotides which binds to the 3’ end of the template DNA strand allowing polymerase to add DNA nucleotides
What does DNA polymerase do during replication?
Adds DNA nucleotides, using complementary base pairing, to the deoxyribose (3’) end of the new DNA strand which is forming
How are the two template strands formed?
DNA is unwound and hydrogen bonds between complementary bases are broken
DNA polymerase can only add DNA nucleotides in one direction from its 3’ end towards its 5’ end, what is the result of this?
The leading strand is replicated continuously and the lagging strand is replicated in fragments
Fragments of DNA are joined together by what?
The enzyme ligase