Higher Biology DNA and the Genome

Eukaryotic cells

Contain a nucleus and other organelles that are bound by membranes.

Where do eukaryotic cells store chromosomes?

They have linear chromosomes in the nucleus and circular chromosomes in mitochondria and chloroplasts

Packing of DNA in eukaryotes

Molecules of DNA are tightly coiled and packaged around bundles of proteins called histones

What does Yeast contain which is unusual for Eukaryotic cells?

Plasmids

What do prokaryotic cells lack?

a nucleus or other membrane bound organelles

What do prokaryotic cells have?

A singular circular chromosome and smaller circular plasmids

What is found inside the nucleus

Chromosomes made of DNA

What does the base sequence of DNA form?

genetic code

What are chromosomes composed of?

DNA and proteins

What does DNA consist of?

nucleotides

What is a nucleotide?

Two long stands of repeated units

What does a nucleotide contain

Phosphate, deoxyribose sugar, one of 4 bases

Name the 4 bases of DNA

Adenine, Thymine, Cytosine, Guanine

What bonds holds the phosphate and sugar of adjacent nucleotides?

Strong chemical bonds

What does antiparallel mean?

The sugar phosphate backbones of the 2 strands run in opposite directions

What kind of bonds form between the bases

weak hydrogen bonds

Describe the structure of DNA

Double stranded antiparallel structure with deoxyribose sugar and phosphate at 3' and 5' ends of each strand forming a double helix

Where can nucleotides be added?

3' end

Replication of DNA

The process by which a double helix of DNA makes an exact copy of itself

When does replication of DNA occur?

Immediately before mitosis

First stage of DNA replication

DNA unwinds and the weak hydrogen bonds break between the bases forming 2 template strands

What happens to the leading strand 3' end

Complementary DNA nucleotides are added continuously to make one new strand

What happens to the lagging strand 5' end

Complementary DNA nucleotides make DNA fragments which must be joined together to make a new strand

What are primers?

Short Complementary sequences of nucleotides that are required at the start of a new DNA strand (only at 3' end)

How is the leading strand formed?

DNA polymerase adds complementary nucleotides to synthesise a complementary strand continuously from 5' to 3'

How is the lagging strand formed?

DNA polymerase adds free complementary nucleotides in fragments. The fragments are joined together by ligase

What is ligase

An enzyme used to join different DNA fragments

Requirements for DNA replication

DNA template, free DNA nucleotides, primers, DNA polymerase, Ligase, ATP

What is the DNA template needed for in replication?

The original strands of DNA form a template for the new complementary strands

What are the free DNA nucleotides needed for in replication?

To make new complementary strands

What are primers needed for in replication?

Needed for DNA polymerase to bind to the start point of a new complementary strand or fragment

What is DNA Polymerase needed for in replication?

Enzyme that adds free nucleotides to make new complementary strand or fragment

What is ligase needed for in replication?

Enzyme that joins the DNA of the lagging strand

What is ATP needed for in replication?

Energy required for DNA replication

What is PCR?

A technique used to amplify DNA fragments in vitro

List the molecules needed for PCR to take place

Heat tolerant DNA Polymerase, DNA template, Primers, Free nucleotides

Where is PCR carried out?

Thermal cycling machine or a water bath

Practical application of PCR

Amplifying DNA for forensic analysis and diagnostic testing for genetic and viral diseases

Step 1 of PCR

DNA is denatured, DNA is heated to 95 degrees to get single stranded DNA

Step 2 of PCR

At 55 degrees the Primers anneal to there complementary sequences

Step 3 of PCR

At 72 degrees DNA is synthesised, heat tolerant DNA polymerase extends the primers by adding DNA nucleotides

Step 4 of PCR

Cycle is repeated

What is gene expression controlled by?

regulation of transcription and translation

What is gene expression?

The process of using information from a gene to synthesise a protein

What is a cells genotype determined by?

The sequence of DNA bases in its genes

What is a cells phenotype determined by?

The proteins that are synthesised when genes are expressed

What are the two steps of protein synthesis?

transcription and translation

What is transcription?

The synthesis of mRNA from a section of DNA

What is Translation?

The synthesis of a protein using instructions from mRNA

What sugar does RNA contain?

ribose sugar

What sugar is found in DNA?

deoxyribose sugar

How many strands does DNA have?

double stranded

How many strands does mRNA have?

Single stranded

Bases in DNA

Adenine, Thymine, Guanine, Cytosine

Bases in mRNA

Adenine, Uracil, Guanine, Cytosine

What does mRNA do?

Carries a copy of the genetic code from the nucleus to the ribosome

What does tRNA do?

Each tRNA molecule carries its specific amino acid to the ribosome

What does rRNA do?

Forms the ribosome with proteins

Properties of mRNA

-Single stranded
-Complementary copy of the gene in the nucleus
-Carries the instructions form making a protein to the ribosome

Properties of tRNA

-A folded single strand of nucleotides with one triplet of bases (anti codon) exposed at the end

Properties of rRNA

-Ribosomes are made of rRNA and proteins
-Ribosomes are the sight of protein synthesis

What is a codon?

Triplet of bases on the mRNA molecule which code for a specific amino acid

What are introns?

Non-coding regions of the Primary mRNA transcript and are removed

What are Exons?

Coding regions and are spliced (joined together) to form mature mRNA transcript

Are the order of exons changed during splicing?

No

1st stage of transcription

RNA polymerase moves along the DNA molecule unwinding the double helix

2nd stage of transcription

RNA polymerase unzips the DNA molecule breaking the weak hydrogen bonds between bases separating the DNA into 2 strands

3rd stage of transcription

RNA polymerase synthesises a primary transcript of mRNA from RNA nucleotides by complementary base pairing

4th stage of transcription

The primary transcription contains coding regions called exons and non coding regions called Introns

5th stage of transcription

During splicing, introns are removed while exons are retained; the exons are then spliced together to form the mature mRNA transcript which leaves the nucleus via a nucleus pore

What is cellular differentiation?

The process by which a cell develops more specialised functions by expressing the genes characteristic of that type of cell

What genes are switched on in all cells?

Genes for vital metabolites

What is a meristem?

A region of unspecialised plant cells which are capable of mitosis producing cells which can then differentiate to produce permanent tissues

What are the 2 types of stem cells?

embryonic stem cells and Tissue(adult) stem cells

What cell is relatively unspecialised in animal cells?

Stem cells

What are tissue stem cells needed for?

Needed for growth and renewal of cells found in that tissue which repairs that tissue are also multipotent

What does multipotent mean?

This means that they can differentiate into all the types of cell found in that particular tissue type

What does pluripotent mean?

All the genes in these stem cells can be switched on and differentiate into any type of cell in that organism