A level Biology 2.5-16

Genes and health

Define Gene.

A section of DNA or a sequence of base in DNA that codes for a sequence of amino acid to make a protein.

Define Genome.

All genes in an individual or a specie.

Define nucleotides

Subunit of nucleic acid that is made up of a sugar, base and phosphate group.

What is the full name of DNA

Deoxyribonucleic acid

What is DNA and what is it role?

DNA is a complex polymer that is made from nucleotides 

Contains genetic information that determines all the inherited characters of an orgainsm

What are the three main features of the structure of DNA?

• Double helix

• polynucleotide

• Anitparallel

Who are the scientists that propose a model of DNA?

(James) Watson aand (Francis) Crick

Who are the scientists thta found the structure of DNA from X rays?

(Maurice) Wilkins and (Rosalind) Franklin

Describe the double helix structure of DNA (4)

• DNA contains multiple nucleotides that have bases attaching with the complementary pair with hydrogen bonds

• Nucleotides bond with each other by strong phosphodiester bonds (in condensation reactions)

• The double strands of nucleotides on each sides are antiparallel( where they have one 5’ and 3’ carbon end)

• Have a deoxyribose sugar

What is a 5’ or 3’ end in the sugar ?

These ends refers to which carbon is attached to the next phospate group

How do you determine which number carbon in the pentagon sugar will be?

The sharp top would be the oxygen, so it doesn’t count.

Then it follows the clockwise direction to count

How and where do phosphodiester bonds form? (2)

By condensation reactions where water are formed and removed.

Phosphodiester bond forms when hydrogen in the phosphate react with OH in the deoxyribose sugar in the sugar-phosphate back bone.

How and what bond is formed between the sugar and base.

A glycosidic bond is formed by reacting the OH in the sugar and the H in the base.

Same by condensation reaction with water as a waste product.

What are purines and which bases are purines.

Purines are bigger bases that have two rings. 

Adenine and Guanine

What are pyramids and which bases are pyramids?

Pyramids are smaller bases and they have a singular ring

Thymine and Cytosine

How do each bases know which one to pair up with (complementary) and which ones pair with each other?

A and T , C and G pair up as purines always pair up with pyramids.

They don’t get mixed because they have different number of hydrogen bonds forming between each other.

A and T have 2 hydrogen bonds while C and G have three hydrogen bonds in between.

What is the ratio between the complementary bases?

1:1

Calculate the percentage composition of C if the A have a 30% composition.

30×2 = 60

100-60 = 40

40/2 = 20

Describe the practicle of seperating DNA from onions with equipments’ functions explained. (7)

1. Mix chopped onions with washing up liquid (breaks membrane) and salt (make DNA clump together) in a beaker

2. Put the beaker in a hot water bath to speed up the reaction

3. Then put it into ice to cool and prevent further denature of DNA

4. Then put the mixture into a blender for no more than 5 secs- helps to break nucleus further

5. Then filter the mixture to seperate cell wall from DNA and protein

6. Then add few drops of protese enzyme to break down the unwanted protein that traps the DNA 

7. Finally pour some ice cold ethanol to the mixture to form white precipitate as DNA is insoluble in ethanol (it needs to be cold to stop or slow down further break down of DNA)

What is RNA’s full name?

ribonucleic acid

What is RNA and its role?

A nucleic acid that copies the genetic information from the DNA by protein synthesis.

What are the differences between DNA and RNA? (7)

• Double and single stranded

• Deoxyribose and ribose sugar

• Contains Thymine and contains Uracil

• Found in nucleus and found in nucleus and cytoplasm

• Permanent and temperary (break down later)

• One basic type and three basic types (m,t,r)

• Conc constant and conc varies

What is the difference between deoxyribose and ribose sugars?

There is an H on the 2’ carbon in deoxyribose sugar while there is an OH on the 2’ carbon in the ribose sugar.

Why does DNA have deoxyribose sugars rather than ribose?

For the stability, deoxyribose sugar don’t have a hydroxly (OH) group at the 2’ carbon on the sugar ring which makes the DNA less reactive and more resistant to hydrolysis compared to RNA.

What happens in transcription? (8)

This happens in the nucleus

It goes in a 5’ to 3’ direction

1. Helicase the enzyme breaks the hydrogen bonds between the bases and unzips the double helix in the DNA

2. One of the DNA strands acts as a template strand that have bases that attracts complemetary free RNA nucleotides (U instead of T) to form hudrogen bonds in between.

3. Another enzyme, RNA polmerase attaches to the template strand and form phosphodiester bonds in the adjacent RNA nucleotides

4. Both enzymes moves along the strand unti it reaches the end of the gene

5. A (pre-) mRNA strand is formed

6. Once the (pre-) mRNA strand is synthesised, RNA polmerase detaches from the DNA which allows it to go back to its double helix structure.

Define template and what is another name for it?

Antisense strand

One of the two strands serves as a pattern to create complementary RNA nucleotides.

It opposites the coding stand.

Define and coding strand and what is another name for it?

Sense trand

One of the two coding strand that is almost the same as the RNA strand that is made in transcription. Instead, Uracil replaces Thymine.

Define introns.

A segment in DNA or RNA that does not code for amino acids or proteins. They needs to be removed 

Define exons

A segment of DNA or RNA that codes for amino acids or proteins.

What happens during RNA spicing? (6)

Happens in the nucleus

1. After transcription where pre- mRNA are made, RNA functionals need to be made to code for proteins.

2. An enzyme, splicesomes removes introns from the pre- mRNA

3. Exons that are left are then rejoined by ligase

4. Pre- mRNA turns into mRNA

5. mRNA leaves the mucleus through nuclar pore 

Define genetic code.

The order of bases in DNA.

Describe 3 properties of the genetic code and what each maan?

1. non- overlapping- it means each nucleotide/base is only read once

2. Triplet codon- the three DNA base codes for one specific amino acid

3. Degernerate code- Last letter of the triplet codon does not make a difference in making the amino acid

What is the start codon?

AUG 

amino acid is- methionine (Met)

What are the stop codons?

UAG, UGA or UAA- they do not code for an amino acid

What are the differences between a triplet and a codon?

Triplet- any 3 nucleotide sequence of DNA

Codon- any 3 nucleotide sequnce of (m) RNA