Year 13 Biology Gene Expression

CELL ULTRA-STRUCTURE Cells can be divided into two general types  The prokaryotes (before the nucleus)  The eukaryotes (true nucleus) Prokaryote  Single celled bacteria and cyanobacteria (blue-green algae)  The chromatin material is not held in a membrane  Chromosome is a simple DNA chain with the ends joined to form a circle  Does not have membrane bound organelles or mitotic apparatus

CELL ULTRA-STRUCTURE Eukaryote  Are all the higher cells other than the bacteria and cyanobacteria that have a true nucleus.  Chromatin material is enclosed within a nuclear membrane  The chromosome is a length of DNA folded. It is wound around proteins  The cells have membrane bound organelles and form spindles during mitosis and meiosis

PROKARYOTIC CELL

EUKARYOTIC CELL

EUKARYOTIC CHROMOSOME STURCTURE The chromosome structure of eukaryote cells are complex in their structure compared to those of prokaryotes. Chromosomes are made up of chromatin (a complex of DNA and protein)

EUKARYOTIC CHROMOSOME STRUCTURE The DNA is coiled at several levels so that long DNA molecules can fit inside the nucleus. The DNA is wrapped around ball-shaped histone protein core. The DNA molecule is a double-helix arrangement of atoms containing genes that comprise many millions of base pairs forming the genetic code

KARYOTYPES The term Karyotype refers to the chromosome complement of a cell or a whole organism. It shows the number, size, and shape of the chromosomes as seen during the metaphase of mitosis. Define: Autosome and Sex chromosome

HUMAN KARYOTYPE

NUCLEIC ACIDS Nucleic acids are a special group of chemicals in cells concerned with the transmission of inherited information. The central nucleic acid is called deoxyribonucleic acid (DNA). It is a major component of chromosomes. All nucleic acids are made up of simple repeating units called nucleotides, linked together to form chains or stands.

NUCLEOTIDE STRUCTURE A nucleotide is made up of three units  Phosphate  Sugar  Base Phosphate – links neighbouring sugars together Sugar – one of two types possible: ribose or deoxyribose Base – comprises the coded genetic message

NUCLEOTIDE BASES The two ringed bases are purines and make the longer bases.  Adenine  Guanine The single-ringed bases are pyrimidines.  Cytosine  Thymine (DNA only)  Uracil (RNA only)

NUCLEOTIDE BASES

BASE PAIRING RULES Adenine always pairs with Thymine (in DNA) Guanine always pairs with Cytosine In RNA Uracil replaces Thymine Bases are joined by hydrogen bonds  2 between A and T  3 Between G and C

NUCLEOTIDE SUGARS Deoxyribose sugar is only found in DNA. It differs from ribose sugar, found in RNA, by the lack of a single oxygen atom

DNA MOLECULE DNA comprises a double strand of nucleotides linked together using the base pairing rules. The way the correct pairs of bases are attracted to each other to form hydrogen bonds is determined by the number of bonds they can form and the shape (length) of the base.

DNA MOLECULE

Template strand – the side of the DNA molecule that stores the information that is transcribed into mRNA. Can be called the antisense strand. Coding strand – the other side, has the same nucleotide sequence as the mRNA. Can be called the sense strand.

RNA MOLECULE RNA – comprises a single strand of nucleotides linked together.

THE GENETIC CODE The genetic information that codes for the assembly of amino acids is stored as three letter codes, called a codon. Each codon represents one of 20 amino acids used in the construction of polypeptide chains, which ultimately form proteins.

THE GENETIC CODE

The genetic code is said to be Degenerate. For each amino acid there may be more than one codon. If a codon only had 2 nucleotides, it would only code for 16 amino acids  4 2 = 16 a.a - this not enough to cover the 20 amino acids  4 3 = 64 a.a – this is more than enough to cover the 20 amino acids

AMINO ACIDS Amino acids are the basic units from which proteins are made. The order of amino acids in a protein is directed by the order of nucleotides in DNA and mRNA. They are linked together by peptide bonds to form long chains of up to several hundred amino acids (called polypeptide chains).

POLYPEPTIDE CHAIN

PROTEINS Proteins are very important chemicals. The word protein comes from the Greek word proteios meaning ‘first place’. They are the main structural chemicals of the body, and they help to run the body by means of enzymes, hormones etc

PROTEINS Proteins are:  The enzymes that catalyse all the biochemical reactions in the body  The structure of the body (hair, muscle, etc)  The carries of oxygen  The fighters of disease  Important parts of cell membranes  Chemical messengers (hormones)

PROTEINS Proteins are polymers, large molecules made up of repeated units. The units are amino acids. There are 20 different amino acids Amino acids are joined by removing a water molecule to form a peptide bond. If two amino acids are joined, a dipeptide is formed; if many amino acids are joined, a polypeptide is formed. A protein is a functional unit made up of one or more polypeptide chains

PROTEIN STRUCTURE Proteins can be long and stringy – the fibrous proteins – or folded into almost circular balls or globs – the globular proteins Scientists have divided the structure into four stages BBC Education - AS Guru - Biology - Biological Molecules - Proteins - Polypetide Folding BBC Education - AS Guru - Biology - Biological Molecules - Proteins - Polypetide Folding

PRIMARY STRUCTURE Amino acid sequence  Hundreds of amino acids link together with peptide bonds to form molecules called polypeptide chains  This sequence is called the primary structure

SECONDARY STRUCTURE α-helix or β pleated sheet  Polypeptides become folded, referred to as the secondary structure.  They are maintained with Hydrogen bonds.  These bonds, although individually are weak, provide considerable strength when there are large numbers of them

TERTIARY STRUCTURE Folding  Every protein has a precise structure formed by the folding of the secondary structure into a complex shape called the tertiary structure.  The protein folds up because various points on the secondary structure are attracted to one another  Disulfide bonds are formed.

QUATERNARY STRUCTURE Some proteins are complete and functional with a tertiary structure only. However, many complex proteins exist as aggregations of polypeptide chains. The arrangement of the polypeptide chains into a functional protein is termed the quaternary structure Example – haemoglobin, a globular protein composed of 4 polypeptide sub-units joined together. Contain 2 identical beta chains and 2 identical alpha chains. Each has a haem group at the centre of the chain, which binds oxygen

QUATERNARY STRUCTURE

PROTEIN STRUCTURES

CELL DIVISION AND MITOSIS Every sexually reproducing organism starts off as a single cell called a Zygote which is formed by the fusion of two sex cells. Each organism must increase in size by cell division, and each new cell formed from the original must carry the total blueprint for that organism, and it must be unchanged.

CELL DIVISION AND MITOSIS The genetic code is carried in the chromosomes so these must be replicated and one of each copy passed onto the two new cells. As the DNA prepares for replication the chromosomes become visible because the long threads of DNA condense and are coiled into much shorter bundles so that they can pass into the new cell without tangling.

MITOSIS - REVIEW Mitosis is the cell division which delivers a complete set of chromosomes into each new cell. It is the cell division for growth and repair One cell division results in two daughter cells Each daughter cell has the same number and kind of chromosomes as the parent cell It does not increase variability as all cells are identical to the parent cell. Complete cut and paste activity, adding notes beside each step (see pg 84/85 Biozone)

MEIOSIS This is the cell division to make gametes (sex cells) in animals and spores in plants. Two cell divisions result in four daughter cells Each daughter cell has half the chromosome number and they are different It increases variability within a population as a result of crossing over and random assortment of chromosomes.

DNA Replication

Protein Synthesis Animation s.swf s.swf