1.1 - The Structure of DNA Flashcards
The Structure of DNA
All cells store their genetic code in the base sequence of DNA. The sequence of DNA bases make up our genotypes (genetic information).
The DNA molecule is made up of two chains of nucleotides forming the double strands of DNA.
DNA is the molecule that holdsthe instructions for growth and development in every living thing.
DNA Nucleotide
The basic units or molecules of DNA are nucleotides.
DNA Nucletotide = phosphate, deoxyribose suagr and a base
The deoxyribose sugar has 5 carbons
Sugar-phosphate Backbone
The phosphate and deoxyribose sugar join to form the sugar-phosphate backbone of DNA.
The bond between the phosphate and deoxyribose suagr is strong.
Complementary Base Pairing
Based that pair up are known as being complementary.
Bases are held together by hydrogen bonds
Bases
Adenine (A) pairs with Thymine (T)
Cytosine (C) pairs with Guanine (G)
5’ to 3’ Ends
The 5’ end joins/bonds at the phosphate group and the 3’ end joins/bonds at the deoxyribose sugar.
Nucleotides are added to the 3’ end to form the chain.
This creates the twisting double helix structure of DNA.
Anti-parallel
DNA is double stranded.
Each strand of DNA runs in opposite directions (anti-parallel) to allow complementary bases to pair up.
DNA is wrapped around proteins called histones.
Organisation of DNA
DNA is present in the cells of every living thing. However, the DNA is organised differently in different types of organism.
We can divide cells into two groups based on how they organise their DNA – eukaryotes and prokaryotes.
Prokaryote
Bacteria are prokaryotes. They sdon’t have a membrane-bound nucleus and their DNA isfree in the cytoplasm.
Prokaryotes have a single, circular chromosome in the centre of the cell that holds all the genes needed for that bacterium.
Prokaryotes also have smaller circular plasmids. These plasmids contain additional genes, such as for antibiotic resistance, which may increase a bacterium’s chance of survival.
Eukaryotes
(All eukaryotes)
Animals, plants and fungi are eukaryotes. They have a membrane-bound nucleus and their chromosomes are linear rather than circular.
Mitochondria and chloroplasts (within eukaryotes)
Circular chromosomes are also found in mitochondria and chlorplasts.
They both use their own DNA to make some proteins needed for their function.
Yeast (special example of a eukaryote)
Yeast is a eukaryote but also contain circular plasmids.
Histones
The DNA found in the linear chromosomes within the nucleus is tightly coiled and packaged around special proteins called histones.
