Biology 12 – the nucleus

Cell structuresIs this eukaryotic? yes

Why? nucleus

Is this a plant or animal cell? animal

Why? No cell wall or chloroplasts

Label the structures

Smooth endoplasmic reticulum

The nucleus

From http://www.bio.jhu.edu/~corces/Research2.html

Nucleus contains DNADNA consists of a double helix tightly coiled

DNA is arranged in chunks called chromosomes

Different species have different numbers of chromosomes

Chromosomes are only visible during cell division

Experiments with the nucleus 1This shows nucleus is responsible for cell survival and division

Experiments with the nucleus 2

This shows nucleus is necessary for normal cell development

Experiments with the nucleus 3

This shows nucleus controls development of special cell structures eg fruiting bodies

Structure of DNA

DNA is a coiled double helix made up of nucleotides on a sugar phosphate backbone

DNA is made of nucleotides

Base pairing

Adenine always pairs with ThymineThymine always pairs with AdenineCytosine always pairs with GuanineGuanine always pairs with Cytosine

Why is DNA important

• It can be inherited (passed on in cell divisions)

• It can easily be copied with a high degree of accuracy

• It controls which proteins are made

DNA controls protein synthesis

Definitions• Transcription• Translation• Codon• Anticodon• t-RNA• m-RNA• r-RNA• Protein• Amino acid

Copying of DNA to make RNA

Reading of mRNA to make proteins

3 unit segment of mRNA – codes for particular amino acid

3 unit segment of tRNA (carrying a particular amino acid) that is the reverse of the codon on mRNA

Carries amino acids to the ribosomeHas the set of instructions for the order in which amino acids are to be assembled into proteins

Makes up the ribosomes, where amino acids are assembled into proteins

Long chains of amino acids, usually folded

Building blocks of proteins

Why are proteins important?

Roles of proteins in the body include

• Structural proteins eg collagen, keratin

• Enzymes (organic catalysts) eg digestive enzymes

• Transport proteins eg haemoglobin

• Regulatory proteins eg hormones

• Protective proteins eg antibodies, clotting factors

RNA is made of nucleotidesVery similar to DNA except: Thymine is replaced by UracilThe sugar in the sugar-phosphate backbone is different (ribose)Strands are single not doubleThere are 3 types – mRNA, tRNA and rRNA

RNA structure

Messenger RNA

Transfer RNA

Ribosomal RNA