Chromosomes/DNA

Chromatin When the cell is not dividing (resting) the chromosomes are all intertwined and are called chromatin.

Chromosomes When the cell starts to divide the Chromosome looks like the above picture before it makes a copy of itself.

46 Chromosomes before they make a copy of themselves 46 Chromosomes before they make a copy of themselves. Note how they occur in Pairs.

Genes are arranged along the DNA of the chromosome Chromosome Structure Chromosomes are made up of 60% protein 40% DNA Genes are arranged along the DNA of the chromosome

Chromosomes which have made a copy of themselves Protein balls called histones DNA

Non Coding DNA Large sections of the chromosome do not contain genes This DNA is called Non Coding DNA It’s function is not yet clear

Chromosome structure

Chromosomes Thread like structures Contains DNA Contains Protein Contains Genetic Information Found in the nucleus of all cells 46 chromosomes in a human cell Occur in pairs

Genes Remember a Gene is a section of DNA that controls the production of a protein. 3% of DNA are genes, the rest is non coding

Structure of DNA-Ordinary Two stranded joined together by bases Bases-Adenine(A), Thymine (T), Guanine (G) and Cytosine (C) Adenine pairs with Thymine Guanine pairs with Cytosine It forms a twisted ladder shape

Structure of DNA- Higher Each strand consists of a phosphate (PO4), a sugar (deoxyribose-5 carbon sugar) and a nitrogen base (A, T, G or C) Phosphate, deoxyribose and base=Nucleotide A and G are Purines T and C are Pyrimdines Bases are bonded by weak hydrogen bonds 2 bonds between A and T 3 bonds between G and C

A Nucleotide Base Sugar P O OH HO NH2 N - OH O CH2 H OH Phosphate 2’ 3’ 4’ 5’ 1’ OH

Purine Bases Adenine and Guanine Double ringed molecular structures O Known as Purine Bases NH2 O N NH Guanine N Adenine NH2

Pyramidine Bases Thymine and Cytosine single ringed structures NH2 Known as Pyramidine bases CH3 N O NH Thymine (DNA) N O NH2 Cytosine

Base Pairing Guanine And Cytosine H O N Guanine - N O H Cytosine + + - - + Three Hydrogen Bonds

Base Pairing Adenine And Thymine - + Adenine CH3 N O H + - Thymine Two Hydrogen Bonds

Double Helix Rosalind Franklin discovered the shape of DNA The outside strand are made from the Phosphate and deoxyribose sugar and the steps are the base pairs These are then twisted to form a spiral structure

Replication Step 1 = DNA uncoils Step 2 = Enzyme breaks weak hydrogen bonds Step 3 = Spare bases enter nucleus & attach to exposed complementary bases. Each side of DNA acts as a template for new DNA Each strand is half new DNA half old DNA Both DNA strands are identical Step 4 = DNA recoils

Step 1

Step 2

Step 3

Step 4

Why is replication important DNA is able to produce exact copies of itself. This means that the same DNA is passed on to each new generation of cells

RNA Ribonucleic Acid Operates with DNA to make proteins Has Uracil instead of Thymine

Differences between DNA and RNA Double strand Sugar is deoxyribose Has Thymine Much longer Self replicating Only in the nucleus RNA Single strand Sugar is ribose Has Uracil Short molecule Not self replicating Found in nucleus and cytoplasm

Similarities between DNA and RNA Both are nucleic acids Both contain adenine, guanine and cytosine nucleotides Operate together to produce specific proteins

PROTEIN SYNTHESIS Higher Level

The Genetic Code A gene is a sequence of many bases required for the production of a particular protein. Proteins (1000s) made from amino acids joined together in a specific sequence 20 different amino acids which can be joined in 1000s of different combinations each producing a new protein DNA codes for the sequence of these amino acids Each amino acid comes from 3 consecutive bases = triplet or codon

Base A, T, C, G Letter A, B, R, T Triplet ATA Word BART Gene ATA GTC CAT GTC ATC… Paragraph Bart had a cat that sat … Genome Book

Gene Expression Remember……… This is the precise way in which the genetic information in a gene is decoded in the cell and used to make a protein.

For Protein Synthesis You need: A supply of amino acids – cytoplasm Instructions as how to join the amino acids together – genetic code An assembly line – ribosomes A messenger to carry information from DNA to ribosomes

Protein Synthesis - Steps 3 stages: 1. Initiation 2. Trancription 3. Translation Remember: DNA  RNA  Protein

Remember RNA Ribose: smaller sugar than deoxyribose of DNA Phosphate 4 Nitrogenous Bases A,G,U,C RNA is single stranded and thus smaller & able to leave the nucleus of the cell

DNA  RNA  Protein Eukaryotic Cell Transcription Translation DNA mRNA Nuclear membrane Transcription RNA Processing Translation DNA mRNA Ribosome Protein Eukaryotic Cell

Prokaryotic Cell – No nucleus DNA  RNA  Protein Transcription Translation DNA mRNA Ribosome Protein Prokaryotic Cell – No nucleus

Learning Check What is RNA composed of? How does RNA (ribonucleic acid) differ from DNA (deoxyribonucleic acid)? What are the three stages in Protein synthesis?

1. Initiation Enzymes in nucleus start to unwind the DNA at the site of the gene.

2. Transcription Eukaryotic Cell DNA mRNA Ribosome Protein Nuclear membrane Transcription Translation DNA mRNA Ribosome Protein Eukaryotic Cell

2. Transcription The transfer of information in the nucleus from a DNA molecule to an RNA molecule. Only 1 DNA strand serves as the template Starts at promoter DNA (AUG) Ends at terminator DNA (stop) When complete, mRNA molecule is released into the cytoplasm

Video Clip available in extra material folder

2. Transcription Takes places in the nucleus of the cell The process by which the information from DNA is transferred to RNA. The exposed DNA bases are matched up with RNA bases in the nucleus to form mRNA.

2. Transcription DNA mRNA RNA Polymerase Enzyme

It was made in the nucleus by transcription from a DNA molecule. This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule. codon A U G G G C U U A A A G C A G U G C A C G U U mRNA molecule

A. Messenger RNA (mRNA) Carries the information for a specific protein. Made up of 500 to 1000 nucleotides long. Made up of codons (sequence of three bases) Each codon is specific for one amino acid.

A. Messenger RNA (mRNA) Primary structure of a protein A U G C aa1 aa2 start codon codon 2 codon 3 codon 4 codon 5 codon 6 codon 7 codon 1 methionine glycine serine isoleucine alanine stop codon protein Primary structure of a protein aa1 aa2 aa3 aa4 aa5 aa6 peptide bonds

3. Translation Eukaryotic Cell DNA Pre-mRNA mRNA Ribosome Protein Nuclear membrane Transcription RNA Processing Translation DNA Pre-mRNA mRNA Ribosome Protein Eukaryotic Cell

Video Clip available in extra material folder

3. Translation Synthesis of proteins in the cytoplasm Involves the following: 1. mRNA (codons) 2. tRNA (anticodons) 3. rRNA 4. ribosomes 5. amino acids

B. Transfer RNA (tRNA) Made up of 75 to 80 nucleotides long. Picks up the appropriate amino acid floating in the cytoplasm Transports amino acids to the mRNA. Has anticodons that are complementary to mRNA codons. Recognizes the appropriate codons on the mRNA and bonds to them with H-bonds.

C. Ribosomal RNA (rRNA) Made up of rRNA is 100 to 3000 nucleotides long. Important structural component of a ribosome. Associates with proteins to form ribosomes.

Ribosomes Large and small subunits. Composed of rRNA (40%) and proteins (60%). Both units come together and help bind the mRNA and tRNA.

Ribosomes Large subunit mRNA A U G C Small subunit

3. Translation Three parts: 1. initiation: start codon (AUG) 2. elongation: 3. termination: stop codon (UAG)

Translation In the cytoplasm, translation occurs. The mRNA binds to a ribosome. The strand of mRNA is pulled through the ribosome three bases at a time, in triplets. Each of these triplets on the mRNA strand is called a codon.

tRNA Transfer RNA (tRNA), reads the strand of mRNA and translates it into a strand of amino acids. A molecule of tRNA has at one end a set of three bases that will complement the mRNA strand; this is called the anticodon.

tRNA If the 3 base anticodon of the tRNA complements the 3 base codon of the mRNA, they briefly combine. The amino acid is left behind when the tRNA leaves. As each codon is read, the next tRNA brings in a new amino acid and the polypeptide (protein) chain grows. This requires enzymes and ATP.

It was made in the nucleus by transcription from a DNA molecule. This is a molecule of messenger RNA. It was made in the nucleus by transcription from a DNA molecule. codon A U G G G C U U A A A G C A G U G C A C G U U mRNA molecule

A ribosome attaches to the mRNA molecule. A U G G G C U U A A A G C A G U G C A C G U U

Amino acid U A C tRNA molecule A transfer RNA molecule arrives. It brings an amino acid to the first three bases (codon) on the mRNA. anticodon The three unpaired bases (anticodon) on the tRNA link up with the codon. A U G G G C U U A A A G C A G U G C A C G U U

U A C C C G Another tRNA molecule comes into place, bringing a second amino acid. Its anticodon links up with the second codon on the mRNA. A U G G G C U U A A A G C A G U G C A C G U U

C C G A A U Another tRNA molecule brings the next amino acid into place. A U G G G C U U A A A G C A G U G C A C G U U

C C G C C G A peptide bond joins the second and third amino acids to form a polypeptide chain. A U G G G C U U A A A G C A G U G C A C G U U

A C G G U C The process continues. The polypeptide chain gets longer. This continues until a termination (stop) codon is reached. The polypeptide is then complete. A U G G G C U U A A A G C A G U G C A C G U U

End Product The end products of protein synthesis is a primary structure of a protein. A sequence of amino acid bonded together by peptide bonds. aa1 aa2 aa3 aa4 aa5 aa200 aa199

Functional Protein The protein now has to undergo folding and the addition of bonds Folding allows the Protein to reach its 3D (Tertiary Shape) which influences its Function.

Types of RNA Three types of RNA: A. messenger RNA (mRNA) B. transfer RNA (tRNA) C. ribosome RNA (rRNA) Remember: all produced in the nucleus!

Learning Check The anticodon UAC belongs to a tRNA that recognizes and binds to a particular amino acid. What would be the DNA base code for this amino acid?

Answer: tRNA - UAC (anticodon) mRNA - AUG (codon) DNA - TAC

What have you learned? Can you ………………  Outline the steps in protein synthesis Understand that a strand of DNA is copied by transcription Understand the role of mRNA Know the function of a ribosome in protein synthesis Understand the process of translation that leads to the formation of a new protein Know that the shape of a protein determines its function

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