Topic 2: DNA structure Flashcards
Define gene (1 point)
- A gene is a SECTION OF DNA that codes for a sequence of amino acids in a polypeptide chain (a protein).
e. g. CFTR protein gene codes for the CFTR protein
What is a mutation? (1 point)
- A mutation is the change in the base sequence of DNA.
Mutations can take place during ____ ________, when
the DNA is ____ ________ ___________.
DNA replication
not copied correctly
DNA is a type of _______ _____.
nucleic acid
DNA is found in the ______ of almost every cell.
nucleus
DNA contains the ________ _____ which controls which _______ are made in the cell, which in turn controls all the inherited _____________ of an organism.
genetic code
proteins
characteristics
DNA is _______ to an organism. (except identical twins)
unique
Name the 2 main nucleic acids
- DNA (deoxyribonucleic acid)
2. RNA (ribonucleic acid)
DNA is a ________.
The monomers that make up DNA and RNA (nucleic acids) are called ________________.
polymer (polynucleotide)
mononucleotides
Label a mononucleotide (on flashcard)
Phosphate
Base
Pentose sugar
Key Summary: Describe the structure of a mononucleotide
4 points
- It contains a pentose sugar (deoxyribose in DNA/ribose in RNA)
- It contains ONE organic base ( A C G T in DNA / A C G U in RNA)
- It contains a phosphate
- It is made of the elements C, H, O, N and P
Key Summary: Give 1 similarity between the structure of a DNA and RNA mononucleotide
(1 similarity)
SIMILARITIES:
1. Both contain a pentose sugar, organic base and phosphate
Key Summary: Give 2 differences between the structure of a DNA and RNA mononucleotide
(2 differences)
DIFFERENCES:
1. A DNA mononucleotide contains deoxyribose, an RNA mononucleotide contains ribose
- A DNA mononucleotide can contain thymine, an RNA mononucleotide can contain uracil
Key Summary: Describe the structure of DNA
4 points
- MADE OF MANY MONONUCLEOTIDES (each contains deoxyribose, one base and phosphate) JOINED BY PHOSPHODIESTER BONDS (between sugar and phosphate) IN CONDENSATION REACTIONS
- DOUBLE HELIX - 2 STRANDS
- COMPLEMENTARY BASE PAIRS HELD TOGETHER BY HYDROGEN BONDS (cytosine and guanine, adenine and thymine) holding the 2 strands together
- DNA is a polynucleotide and a nucleic acid
Label the DNA (on flashcard)
- Deoxyribose sugar
- Phosphate
- Base
- Nucleotide
- Sugar-phosphate backbones
Adenine ONLY pairs with _________.
Cytosine ONLY pairs with _________.
Why is this? (3 points)
Thymine
Guanine
- A and G (purines) have a 2 ring structure
- C and T (pyrimidines) have a 1 ring structure
- The bases pair up so there are 3 rings forming each “rung” of the ladder, there are even widths between strands
Two chains are held together by ____________ ________.
The strands run in opposite directions with the ___________ phosphate groups on the outside & the ___________ bases on the inside.
The ______ join in the middle of the helix (like a ladder).
The ________ and ___________ form the backbone.
hydrogen bonds
hydrophilic
hydrophobic
bases
sugars
phosphates
Key Summary: Explain how base pairing is involved in the formation of the DNA double helix
(3 points)
- COMPLEMENTARY base pairing - A only pairs with T, C only pairs with G
- Hydrogen bonds form between bases (3 between C and G, 2 between A and T)
- to HOLD the 2 DNA strands of the double helix together
Key Summary: Explain how hydrogen bonding is involved in the formation of the DNA double helix
(2 points)
- Hydrogen bonds form BETWEEN complementary base pairs (A and T, C and G)
- to HOLD the 2 DNA strands of the double helix together
If 36% of bases in a DNA molecule are A, what percentage of bases are G?
G = 14%
WORKING OUT:
If 36% of the bases are A, then 36% of the bases are T
So if you add up the percentages of these bases 36 + 36 = 72%
Then if you subtract 72% from 100% 100 – 72 = 28%
So 28% of the bases must be C and G and they are present in equal numbers
28 divided by 2 = 14
So 14% of the bases are C and 14% of the bases are G
A = 36% T = 36% G = 14% C = 14%
Key Summary: Describe the structure of RNA
5 points
- MADE OF MANY MONONUCLEOTIDES (each contains ribose pentose sugar, one organic nitrogenous base and phosphate)
- PHOSPHODIESTER BONDS, BETWEEN SUGAR AND PHOSPHATE, join mononucleotides in condensation reactions
- SINGLE STRANDED
- RNA is a polynucleotide
- RNA is a nucleic acid
Key Summary: Compare the structures of DNA and RNA
3 similarities
SIMILARITIES:
1. Both polynucleotides made up of many mononucleotides joined by phosphodiester bonds
- Both CONTAIN bases adenine, cytosine, guanine
- Both have sugar-phosphate backbone with bases sticking out from it
Key Summary: Contrast the structures of DNA and RNA
3 differences
DIFFERENCES:
1. RNA is single stranded and DNA is double stranded
- The sugar in RNA is ribose, but the sugar in DNA is deoxyribose
- RNA CONTAINS the base uracil, but DNA contains thymine
