Higher Biology - Unit 1

Describe the shape of DNA

Double stranded helix

What is a nucleotide made up of?

Deoxyribose sugar, phosphate, base

Which carbon is the phosphate attached to?

5’

What are the four bases?

Adenine, Cytosine, Guanine, Thymine

What are the complementary base pairs?

Adenine and Thymine, Cytosine and Guanine

What are base pairs held together by?

Weak hydrogen bonds

Why does DNA with a higher proportion of C-G base pairs than A-T base pairs need more energy to be separated?

Because there are more hydrogen bonds between C-G base pairs than between A-T base pairs

What does antiparallel mean?

The DNA strands run in opposite directions to each other

What does the base sequence of DNA form?

The genetic code

Describe the organisation of DNA in prokaryotes

• No distinct nucleus

• A single circular chromosome

• Smaller circular plasmids

Describe the organisation of DNA in eukaryotes

• Linear chromosomes in the nucleus (associated with histone proteins)

• Circular chromosomes in mitochondria and chloroplasts

• Yeast cells are the only eukaryote that have plasmids

Which organelles contain their own DNA?

Mitochondria, chloroplasts (in photosynthetic eukaryotes)

What is DNA replication?

The process in which DNA makes identical copies of itself

What enzyme replicates DNA?

DNA polymerase

What is a primer?

A short strand of complementary nucleotides

Why are primers needed to start replication?

They allow polymerase to add DNA nucleotides by binding to the 3' end of the leading strand

What unwinds the DNA strand?

Helicase

What happens when the DNA strand is unwound?

The hydrogen bonds between the bases are broken and a replication fork is formed

What adds nucleotides to the DNA strand?

DNA polymerase, using complementary base pairing from 3' to 5'

Which direction can DNA polymerase only add nucleotides in?

3' to 5'

How is the leading strand replicated?

Continuously

How is the lagging strand replicated?

Discontinuously, in fragments

What are fragments of DNA on the lagging strand joined together with?

Ligase

Why is DNA replication important?

It ensures that identical copies of genetic information are passed through generations of cells

What is the Polymerase Chain Reaction? (PCR)

A laboratory technique used for the amplification of DNA in vitro

How does PCR amplify DNA?

By using complementary primers for specific target sequences

What are the requirements for DNA replication?

DNA polymerase, ATP, primers, ligase, DNA templates, free DNA nucleotides

What temperature is DNA heated to in the first stage?

95°C

What temperature is DNA cooled to in the second stage?

55°C

What temperature is DNA heated to in the third stage?

75°C

Why is DNA heated in the first stage?

To separate the strands of DNA

Why is DNA cooled in the second stage?

To allow primers to bind to target sequences

Why is DNA heated in the third stage?

For heat-tolerant polymerase (e.g. taq polymerase) to replicate the region of DNA

Why is heat-tolerant polymerase used?

Because it can withstand the high temperatures required for PCR without denaturing

What are three practical applications of PCR?

Paternity testing, forensics and diagnosing genetic disorders

What is gel electrophoresis?

A method for separating macromolecules, such as fragments of DNA, based on their size and electrical charge (shorter fragments move faster and further than longer ones)

How would you use PCR and gel electrophoresis to identify the origin of a tiny sample of DNA from a crime scene?

• The sample would undergo PCR to amplify the DNA

• DNA would be cut by restriction endonuclease

• Fragments would be stained and added to a gel

• An electric current is applied to gel, producing a DNA profile

What is gene expression?

The process by which specific genes are activated to produce a required protein

What processes does gene expression involve?

Transcription and translation

What types of RNA are involved in gene expression?

mRNA, rRNA, tRNA

What is RNA made up of?

Ribose sugar, phosphate, base

What are three differences between DNA and RNA?

• DNA has deoxyribose sugar, RNA has ribose sugar

• DNA is double stranded, RNA is single stranded

• DNA contains the base thymine, RNA contains the base uracil

What is the role of mature messenger mRNA?

To carry a copy of the genetic code from the nucleus to the ribosome

Where does transcription take place?

The nucleus

Where does translation take place?

The ribosome

What is a triplet of bases called?

A codon

What is the function of codons?

To code for specific amino acids

Why does tRNA fold?

Due to complementary base pairing

Describe a tRNA molecule

Each tRNA molecule has an anticodon at one end and an amino acid attachment site on the other end

What is the function of tRNA?

To carry its specific amino acid to the ribosome

What is the ribosome made up of?

Protein and rRNA

What is the product of transcription?

mRNA

Which enzyme unwinds DNA for transcription?

RNA polymerase

What is the function of RNA polymerase in transcription?

To unwind the DNA and synthesise a primary transcript of mRNA from RNA nucleotides by complementary base pairing

What are introns?

Non-coding regions in the primary transcript which are removed after splicing

What are exons?

Coding regions which are joined together to form the mature transcript

What does RNA splicing form?

The mature mRNA transcript

What is produced by translation?

A polypeptide chain

Where does translation begin?

At a start codon

Where does translation stop?

At a stop codon

How does the tRNA anticodon attach to mRNA codons?

By complementary base pairing

What happens when the tRNA anticodon attaches to mRNA codons?

The genetic code is translated into a sequence of amino acids

What holds amino acids together?

Peptide bonds

What happens when polypeptides have been formed?

tRNA exits the ribosome to collect more amino acids

How can different proteins be expressed from the same primary transcript?

By alternative RNA splicing as different proteins are produced depending on what combination of the exons are kept

What happens when a polypeptide folds?

It forms a 3D protein

What determines the function of a protein?

Its shape

What determines the phenotype of an organism?

Proteins and environmental factors

What are two groups of proteins found in living cells?

Structural, enzymes

What is cellular differentiation?

The process by which a cell expresses certain genes to produce proteins that are characteristic for that type of cell

What does cellular differentiation allow?

It allows a cell to carry out specialised functions

What are meristems?

Regions of unspecialised cells in plants that can divide (self-renew) and differentiate

What are stem cells?

Unspecialised cells in animals that can divide (self-renew) and differentiate

What does multipotent mean?

Refers to stem cells which can only differentiate into cell types of that tissue

What does pluripotent mean?

Refers to stem cells which can differentiate into all cell types of that organism

Are tissue stem cells multipotent or pluripotent?

Multipotent

Are embryonic stem cells multipotent or pluripotent?

Pluripotent

Why are tissue stem cells multipotent?

Because only some of their genes can be switched on

Why are embryonic stem cells pluripotent?

Because all of their genes can be switched on

What are tissue stem cells involved in?

The growth, repair and renewal of cells found in that tissue

What are two examples of therapeutic uses of stem cells?

• corneal repair

• skin graft repair

What are two examples of research uses of stem cells?

• Used as model cells to study how diseases develop

• Drug testing

What information does stem cell research provide?

How cell processes such as growth, differentiation and gene regulation work

What are two ethical concerns on the use of embryonic stem cells?

• They can offer effective treatments for disease and injury

• But involves the destruction of an embryo, meaning the loss of a potential human life

What is the genome?

An organism's entire hereditary information encoded in DNA

What is the genome made up of?

Genes

What are genes?

DNA sequences that code for protein, and other DNA sequences that do not code for proteins

Is the genome in eukaryotes mostly coding sequences or non-coding sequences?

Non-coding sequences

What are non-coding sequences involved in?

Some regulate transcription, others are transcribed into RNA but not translated

What are two non-translated forms of RNA?

rRNA and tRNA

What are mutations?

Changes in DNA that can result in no protein or an altered protein being synthesised

What are the types of single gene mutation?

Insertion, deletion and substitution

What are the types of substitution mutations?

Missense, nonsense and splice-site

What is a missense mutation?

Mutation where one amino acid is changed for another

What does a missense mutation result in?

A non-functional protein being produced or have little effect on the protein

What is a nonsense mutation?

Mutation where a premature stop codon is produced

What does a nonsense mutation result in?

A shorter protein being produced

What is a splice-site mutation?

Mutation where some introns are retained and/or some exons are not included in the mature transcript

What does a splice-site mutation result in?

A non-functional protein being produced

What do insertion and deletion mutations result in?

A frame-shift mutation