Biology Topic 2 Part 1- Genes and health

Who discovered the structure of DNA

Watson and Crick

Where is DNA located

The nucleus

What is the role of DNA

Contains the genetic code and controls the manufacturing of proteins

What is a polypeptide chain

A chain of amino acids linked together by peptide bonds.

What are the Bases of DNA

Adenine, Thymine, Guanine, Cytosine

What are the bases of RNA

Adenine, Uracil, Guanine, Cytosine

What are the types of nitrogenous bases

Adenine, Thymine, Cytosine, Guanine

What is the name of a basic unit that makes up DNA

Nucleotide

What are nucleotides

The basic unit that makes up DNA

What are the basic components of nucleotides

-pentose sugars

-phosphate group

-Nitrogen-containing base (A,T,C,G)

What type of acid is DNA

deoxyribonucleic acid

How are nucleotides formed

condensation reactions between a pentose sugar, nitrogen containing base and phosphate group

What part of a nucleotide is variable

nitrogenous base

How do mononucleotides link together

Through condensation reactions between the sugar of one nucleotide and phosphate of the next one

What is a chain of nucleotides known as

polynucleotide

What bonds form between nucleotides

phosphodiester bonds

What is the double helix

two polynucleotides wrapped around each other

What forms the backbone of a DNA molecule

sugar and phosphate

What does it mean for DNA to be antiparallel

It means that each strand goes in an opposite direction length-wise, but is still parallel.

What are the base pairs

Adenine with Thymine and Guanine with Cytosine

What determines the base pairings

The number of hydrogen bonds each base pair can form and the size of each base

What is a Purine base

A base with 2 rings

What is a pyrimidine base

A base with one ring

What are the purine bases

Adenine and Guanine

What are the pyrimidine bases

Cytosine and Thymine

Why do the sizes of the bases dictate the base pairings

There is only space between the two strands for one purine base and one pyrimidine base. Having two purine bases would create a dent in the structure, effecting its stability, while having two pyrimidine bases would leave a gap two large for hydrogen bonds to be formed

Why does the amount of hydrogen bonds a base can form dictate the base pairings

They pair up in a way to create the most hydrogen bonds possible, making the structure of the DNA molecule as strong as it can be

How many bonds do Adenine and Thymine form

2 hydrogen bonds

How many bonds do Guanine and Cytosine form

3 hydrogen bonds

Where is DNA found in eukaryotes

in the nucleus, mitochondria, and chloroplasts

Where is DNA found in prokaryotes

nucleoid region and plasmids

What is a genome

the full set of genetic information that an organism carries in its DNA

What is a proteome

The full range of proteins that can be synthesised from the genome

What is transcription

The process of making RNA from DNA

What is translation

the decoding of an mRNA message into a protein from a DNA template into amino acids

What is the primary structure of a protein

The sequence of amino acids in a polypeptide chain which determines its properties and shape

What are genes

Sections of DNA that code for polypeptides and functional RNA

What are the 4 main differences between DNA and RNA

DNA is longer than RNA

DNA has two polynucleotides, while RNA has only 1

RNA does not contain Thymine, but contains Uracil instead

RNA's pentose sugar is ribose, rather than deoxyribose

Where does protein synthesis occur

ribosomes

What type of base is uracil

pyrimidine

Explain the Meselson-Stahl experiment

Proved the semiconservative hypothesis

Grew E.coli, exposing it to two isotopes of nitrogen, N15 and N14. N14 is lighter than N15. This helped distinguish between the two DNA densities, as the E.coli exposed to N15 sunk to the bottom of the test tube, while the N14 stayed in the middle.

Semiconservative replication stages

1. Helicase enzymes seperate the two strands of DNA, forming a replication fork

2. DNA strands are kept apart by single strand binding (ssb) proteins

3. DNA polymerase builds new strands, using each parent strand as a template "reading" the sequence of bases and adding their complimentary pairs to form new strands

4. DNA polymerase reads the parent strand 3' to 5' and builds the leading strand 5' to 3'

5. The lagging strand is built 3' to 5' away from the replication fork in sections called Okazaki fragments, which are joined together by DNA ligase

What do helicase enzymes do

Seperate 2 DNA strands

What do single strand binding proteins do

Keep apart DNA strands during replication

What does DNA polymerase do

adds base pairs to DNA during replication

What does DNA ligase do

joins Okazaki fragments together

Describe the process of transcription

1) The DNA double helix is unzipped by DNA helicase and the hydrogen bonds are broken. The DNA helicase moves along the sugar-phosphate backbone, beginning at the start codon

2) The DNA antisense strand acts as a template for the mRNA as free RNA nucleotides pair with the exposed complimenting bases

3) The RNA nucleotides are joined to the adjacent nucleotides by phosphodiester bonds to form the mRNA strand

4) The reaction is catalysed by RNA polymerase which travels along the backbone in the 3' to 5' direction

5) The mRNA detatches from the DNA, allowing the double helix to reform

What is splicing

Removing introns from RNA and sealing exons together. This happens in eukaryotes, as the introns do not code for proteins, so need to be removed from the pre-mRNA to make mature mRNA

What is the sense strand

the DNA strand which has the same base sequence as the mRNA with thymine instead or uracil 5'→3'

What is the antisense strand

template strand

What is the triplet code

the genetic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, three-nucleotide words

What does it mean for the triplet code to be degenerate

Each amino acid is coded for by more than one triplet

Describe the process of translation

1) mRNA enters the cytoplasm through nuclear pores and associates with a ribosome, binding to the small subunit at the start codon

2) The first tRNA molecule with the complementing anticodon binds to the start codon by hydrogen bonding. Each tRNA is specific for one amino acid

3) A second tRNA molecule with a complementing anticodon is able to bind to the next mRNA codon

4) A peptide bond is formed between the two amino acids and the first amino acid is released from the first tRNA

5) The ribosome moves along the mRNA strand and the first tRNA is released

6) The cycle repeats forming a long polypeptide chain

7) Once a stop codon is reached, no tRNA's can bind and the synthesised polypeptide is released