DNA Structure and Replication Higher Human Biology
Learning Intention Describe the structure of DNA Explain the base pairing rule using adenine, thymine, cytosine and guanine
1 Division and differentiation in human cells What is the name of the process by which a cell develops more specialised functions by expressing the genes characteristic for that type of cell. Cellular differentiation What name is given to cells which are relatively unspecialised cells that can continue to divide and can differentiate into specialised cells of one or more types. Stem cells Why are stem cells capable of becoming many cell types? Most of their genes are still active During embryological development the unspecialised cells of the early embryo change into cells with specialised functions. What term is used for this? differentiation
Describe what happens to genes as cells specialise. Most genes are switched off with only essential genes and specialised genes still active Tissue (adult) stem cells have two functions. What are they? replenish differentiated cells that need to be replaced give rise to a more limited range of cell types. What are somatic cells? Cells with diploid set of chromosomes Somatic cells divide by what process to form more somatic cells? mitosis Somatic cells differentiate to form different body tissue types: - Can you name them? epithelial, connective, muscle and nerve
What are germline cells and where are they found? Cells which give rise to sex cell in testes and ovaries Germline cells divide to produce more germline cells or to produce haploid gametes. What two types of cell division are involved? mitosis and meiosis Are mutations in germline cells are passed or somatic cells passed to offspring? Germline only Give an example of a tissue which can be repaired using stem cells Cornea Give an example of an organ which can be repaired using stem cells. Heart, Brain
secondary tumours Give one example of a therapeutic use for stem cells Reverse the effects of damage caused by heart attack, stroke or MS Give one other use of stem cell by drug companies in the lab. Stem cells can be used as model cells to study how diseases develop or for drug testing. Give one example of an ethical issue resulting from use of of stem cell use. Embryonic stem cells involve the destruction of cells which have the potential to give rise to a new life Give two features of cancer cells Cancer cells divide excessively to produce a mass of abnormal cells (a tumour) that do not respond to regulatory signal Cancer cells may fail to attach to each other. If the cancer cells fail to attach to each other they can spread through the body to form what?
Lesson starter 1. Give two features of cancer cells Cancer cells divide excessively to produce a mass of abnormal cells (a tumour) that do not respond to regulatory signal Cancer cells may fail to attach to each other. 2. If the cancer cells fail to attach to each other they can spread through the body to form what? secondary tumours 3. What is the difference between pluripotent and multipotent and give the name of associated stem cell 4. What is the difference between haploid and diploid?
Today we are moving onto look at DNA Write down everything you remember about DNA! You have 5 minutes
DNA Structure DNA consists of units called nucleotides. Nucleotides are made of 3 parts:
Deoxyribose Sugar The deoxyribose consists of 5 carbon atoms:
Nucleotides There are 4 different types of nucleotide, depending on the base that they have:
Base Pairing Certain bases are complementary to each other, this is called the base pairing rule. A only pairs with T and C only pairs with G. Bases in adjacent strands are held together by weak hydrogen bonds.
DNA Strand An individual strand of DNA is held together by a strong peptide bond between the phosphate of one nucleotide and the carbon 3 of the sugar on another nucleotide. Strong chemical bond
DNA Molecule When a DNA strand is held together by this chemical bond, and then joined to a second strand by hydrogen bonds between the bases, this makes it coil into a double helix structure. glow clip
Antiparallel Strands A DNA strand s 3 end has a deoxyribose sugar and the 5 end has a phosphate. Nucleotides can only be added to the 3 end. The 2 DNA strands have their sugar-phosphate backbones running in opposite directions. 3" 5" explained
Anti-Parallel The double helix is described as having two anti-parallel chains of nucleotides because one side goes from 5 to 3 and the opposite side goes from 3 to 5.
Learning Intentions Explain the importance of DNA as a unit of inheritance Describe chromosome structure
Inheritance DNA is important because it is how all cells store genetic information. The base sequence of DNA determines genotype. DNA is found in the nucleus of a cell.
Chromosomes DNA is arranged in tightly coiled chromosomes. The DNA is packaged with proteins.
Learning Intention Outline the stages of DNA replication, including the role of DNA polymerase and DNA ligase.
Lesson starter 1. What does DNA stand for? 2. What is DNA? 3. Where is it found specifically in the body? 4. How do we describe the structure of DNA? 5. What 3 things make up a nucleotide? 6. What does the D in DNA stand for? Why? 7. Name the 4 bases and state the rule! 8. What is a chromosome and name 3 parts 9. DNA codes for what?
LESSON STARTER 1. What is the difference between cell reproduction and cell differentiation? Cells reproduce themselves by repeated mitosis whilst remaining undifferentiated Cells differentiate into a diverse range of specialised cells when required to by the organism that possesses them. E.g. unspecialised specialised 2. What are somatic cells? Give an example Somatic cells - Somatic cells are the differentiated cells that form the different types of body tissue that exist (divide by mitosis). Muscle cells form muscle tissue 3. What are germline cells and what can they become? Germline cells - Germline cells include the sex cells or gametes and the cells that produce the gametes called gamete mother cells
Starter Draw and label a DNA nucleotide (including numbering the carbons). Copy the DNA strand below and draw its complementary strand: A A T G G C T A C G T A C T A C A
What s the Question? 1. The 5 end 2. The 3 end 3. Hydrogen bond 4. Protein
Give an account of cell differentiation under the following headings. (i) Stem cells (4) (ii) Somatic cells (4) (iii) Germline cells (2)
DNA Replication DNA replication occurs in the nucleus and involves a DNA molecule unwinding. Once the DNA has unwound, it then unzips to expose its bases. These bases then act as a template for a new DNA strand to be made.
DNA Replication Once the nucleotides are exposed, free floating nucleotides in the nucleus join on to their complementary bases. Y-SHAPED REPLICATION FORK This happens continuously along the DNA strand.
DNA Replication Once the nucleotides are lined up, they join to their partner by hydrogen bonds. The DNA strand then forms a sugar phospate backbone.
DNA Replication The DNA strands then wind back up to form 2 identical double helix. Each double helix contains one original strand and one new strand.
Semi-conservative replication Replication results in two new DNA molecules. It is said to be SEMI- CONSERVATIVE because each new DNA molecules receives one strand of the original parent molecule.
A T C G T A G C C G A T A C T G C A T G A C G T
A T A T C G C G T A T A G C G C C G A T T C G A C A T G
A T A T C G C G T A T A G C G C C G C G A T A T
5. Sugarphosphate bonds form 6. Daughter DNA molecules form 4. Weak hydrogen bonds form between bases 3.. Free nucleotides from nucleoplasm find complementary bases 2. Hydrogen bonds break and DNA unzips 1. Parent DNA unwinds Warning this gives the stages but not the correct orientation for both strands as it is too difficult to do just now.
Copied DNA 2 Daughter DNA strands Original DNA
This process can only take place if the nucleus contains: DNA (acts as template for new molecule) Supply of DNA nucleotides Appropriate enzymes DNA Polymerase & Ligase Supply of ATP Primer
Enzyme Control of Replication DNA polymerase is an enzyme that controls the sugar-phospate bonding of the nucleotides into the DNA strand. This enzyme can also add nucleotides to the strand, but only add nucleotides to a pre-exsisting chain so for it to work, a primer must be present. A primer is a short sequence of nucleotides at the 3 end.
Lesson starter 1. List 3 things required for DNA Replication 2. What happens after DNA has unzipped? 3. What is a primer? 4. What is the role of DNA polymerase?
The DNA template strand that has the 5 end has to be replicated in fragments, each starting at the 3 end of a primer Primer **DNA IS ALWAYS BUILT FROM THE 5 END 3 END https://www.youtube.com/wa tch?v=vnxfk_d6y80 https://www.youtube.co m/watch?v=cdwjtlng Eyw Primer https://www.youtube.com/watch?v=5qsrmeiwsuc
Enzyme control DNA is a complex process that involves many enzymes The section of DNA that is to be replicated unwinds and unzips creating a y-shaped replication fork (helicase). The important thing to learn is that DNA can only build in the direction 5 3. This means that nucleotides can only be added to the 3 end by an enzyme polymerase
5 This is the parent opening like a zip 3 UNZIP PING POINT HERE 3 5 3 5 3 5 This can build continuously in the correct direction 5 3 TOWARDS the point where the unzipping point This 5 3 Can only be built 5 3 AWAY from the unzipping point so must be built in sections which are glued together
5 This is the parent opening like a zip 3 UNZIP PING POINT HERE 3 3 5 3 3 5 5 This can build continuously in the correct direction 5 3 TOWARDS the point where the unzipping point This 5 3 Can only be built 5 3 AWAY from the unzipping point so must be
On the leading strand The enzyme DNA polymerase controls the sugar-phosphate bonding between nucleotides on the new DNA strand. This will only work if it has two nucleotides to join. Therefore a primer is needed to initiate DNA replication. A primer is a short strand of complementary nucleotides formed at the 3 end of the parental DNA strand. DNA replication on this strand is continuous
On the lagging strand DNA polymerase can only add nucleotides to the free 3 end of a growing strand. Therefore the DNA on the parental strand that has the 5 end exposed is replicated in fragments starting at the 3 end of a primer. As the replicated strand is discontinuous, the enzyme LIGASE joins the fragments together
http://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter14/dna_replica
DNA and the bigger picture Once the two identical daughter DNA strands form, they coil up and become IDENTICAL CHROMATIDS (held together by a centromere). Following DNA replication (and before cell division) the cells DNA content is at its maximum. DNA replication ensures that an exact copy of a species genetic information is passed on. If DNA failed to replicate itself, mitosis and meiosis would be unable to take place. DNA is essential for life to exist.
5 end of DNA strand DNA polymerase enzyme Leading strand of replicated DNA 3 end of DNA strand Primer Start of complementary strand of replicated DNA Replication of the leading strand of DNA
Replication of the lagging strand of DNA 3 end of DNA strand Primer DNA polymerase Ligase 5 end of DNA strand
Ligase Once the DNA fragments are all in place, the enzyme ligase joins the fragments together. dna replication rap
When copying a long chromosome many replication forks operate simultaneously to speed up the replication process.
Requirements for Replication For DNA replication to occur, the nucleus must contain: DNA (Template) Primers Supply of 4 types of nucleotide Enzymes (ligase and DNA polymerase) ATP
Video Summary Summary (includes structure of RNA) Video Skip from 5:40 to 9:10