Unit 4: DNA structure, Replication, Reproduction

3.1 Explain how traits are determined by the structure and function of DNA 3.1.1

Explain the double-stranded, complementary nature of DNA as related to its function in the cell. Unpacking:• Develop a cause-and-effect model relating the structure of DNA to the functions of replication and protein synthesis:

o The structure of DNA is a double helix or “twisted ladder” structure. The sides are composed of alternating phosphate-sugar groups and “rungs of the DNA ladder” are composed of complementary nitrogenous base pairs (always adenine, A, to thymine, T, and cytosine, C, to guanine, G) joined by weak hydrogen bonds.

o The sequence of nucleotides in DNA codes for proteins, which is central key to cell function and life.

o Replication occurs during the S phase of the cell cycle and allows daughter cells to have an exact copy of parental DNA.

o Cells respond to their environments by producing different types and amounts of protein. o With few exceptions, all cells of an organism have the same DNA but differ based on the

expression of genes. • Infer the advantages (injury repair) and disadvantages (cancer) of the overproduction, underproduction or production of proteins at the incorrect times.

1.1.3

Explain how instructions in DNA lead to cell differentiation and result in cells specialized to perform specific functions in multicellular organismsUnpacked:• Compare a variety of specialized cells and understand how the functions of these cells vary. (Possible examples could include nerve cells, muscle cells, blood cells, sperm cells, xylem and phloem.) • Explain that multicellular organisms begin as undifferentiated masses of cells and that variation in DNA expression and gene activity determines the differentiation of cells and ultimately their specialization.

o During the process of differentiation, only specific parts of the DNA are activated; the parts of the DNA that are activated determine the function and specialized structure of a cell.

o Because all cells contain the same DNA, all cells initially have the potential to become any type of cell; however, once a cell differentiates, the process cannot be reversed.

o Nearly all of the cells of a multicellular organism have exactly the same chromosomes and DNA.

o Different parts of the genetic instructions are used in different types of cells, influenced by the cell's environment and past history.

• Recall that chemical signals may be released by one cell to influence the development and activity of another cell. • Identify stem cells as unspecialized cells that continually reproduce themselves and have, under appropriate conditions, the ability to differentiate into one or more types of specialized cells.

o Embryonic cells which have not yet differentiated into various cell types are called embryonic stem cells.

o Stem cells found in organisms, for instance in bone marrow, are called adult stem cells. o Scientists have recently demonstrated that stem cells, both embryonic and adult, with

the right laboratory culture conditions, differentiate into specialized cells. Note: It is not essential for students to understand the details of how the process of transcriptional regulation in a cell produces specific proteins, which results in cell differentiation.

DNA StructureDNAo Deoxyribonucleic acid: codes for genetic information.o Provides the instructions for making proteinso Codes for traits (characteristics)

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Test Date: ___________________

o Where is it found in the cell? -> Nucleus. ** cannot leave the nucleuso Structure of DNA

Polymer: DNA Monomer or Subunits: nucleotides Double Helix: (2 strands) James Watson and Frances Crick discovered the structure of DNA. Nucleotide: made of 3 parts

1. sugar: deoxyribose 2. Phosphate group 3. Nitrogen bases (one of the following)

o Adenineo Thymine

o Guanineo Cytosine

Label the 3 parts of this nucleotide

Shape of DNA

Shape of DNA is a “Twisted ladder”: Backbone: repeating phosphate

and sugars Rungs: nitrogen bases (held

together by hydrogen bonds)

Nitrogen Bases: Purines: 2 rings-- adenine and

guanine Pyrimidines: 1 ring—cytosine and

Thymine

Complementary Base Pairing A always pairs with T C always pairs with G

Make the compliment DNA to this: A T C G C C C A A = ___________________________________

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Identify the parts of this DNA strand:

W: ______________________________________

X: _______________________________________

Y: _______________________________________

Z: _______________________________________

What type of bond is between W and X? _______________________________________

DNA REPLICATION

o DNA Replication Replication: DNA synthesis -> makes new DNA Synthesis -> means to make

Makes an exact copy of DNA Why? For new cells that will be made When? -> during interphase of the cell cycle Where? -> inside the nucleus

Steps of Replication 1. An enzyme called helicase unzips the double helix. 2. A new strand of DNA is made along each template (old) strand – (Polymerase is

the enzyme that puts the new strand with the old strand) 3. Result- 2 molecules of DNA (each with a new strand and old strand) ** semi

conservative nature**

Diagrams of DNA Replication

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Compare the two new strands of DNA: _________________________________________________________

1.2 Analyze the cell as a living system1.2.2

Analyze how cells grow and reproduce in terms of interphase, mitosis and cytokinesis. Unpacked:• Outline the cell cycle – Growth1, Synthesis, Growth2, Mitosis, and Cytokinesis. • Recognize mitosis as a part of asexual reproduction. (middle school review) • Organize diagrams of mitotic phases and describe what is occurring throughout the process. Note: When students learn about meiosis (Bio.3.2.1), they should compare it to the process of mitosis.

Cell Reproduction: The Cell Cycle

Cell Reproduction: Essential for life to continueo Occurs when the surface area of a cell becomes to small for the volume of the cell.

Cells important material is DNA. Can be in two forms:4

Chromatin: all the DNA, thin and threadlike unwound pieces of DNA. Chromosome: condensed chromatin, tightly packed, visible structures. Chromosomes are

rod-shaped structures of DNA that carry genes. They are made up of two sister chromatids and a centromere that holds them together.

Label the parts of the chromosome: centromere, gene, chromosome, chromatids

The Cell Cycle : life cycle of the cell. Has 3 parts

Label the parts of the cell cycle:

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Base pairs

Cell

Nucleus

Centromere

DNA

1. Interphase: includes G1, S, and G2o G1: Cell grows, increases in size by adding materials.o S: chromosomes double, DNA copies itselfo G2: cell is preparing to divide

2. Mitosis: the division of the nucleus. Has 4 steps.o Step 1: Prophase: chromatin cols up into chromosomes and attaches to its identical copy

(sister chromatids that are joined by centromere) Nuclear membrane disappears Centrioles begin to move to opposite ends of the cell Spindle fibers begin to form between two centrioles

o STEP 2: Metaphase: spindle fibers attach to centromere sister chromatids and they line up in the middle of the cell

o Step 3: Anaphase: spindle fibers shorten and pull the sister chromatids apart to opposite ends of the cell

o Step 4: Telophase: chromatids uncoil and turn back into chromatin Spindle fibers break down 2 new nuclear membranes begin to form around the 2 groups of chromatin

Product of mitosis: 2 daughter cells with identical genetic material (DNA)

3. Cytokinesis occurs: the cell begins to divide into 2 cells, division of the cytoplasm. Animal cells: cells pinch and form a cleavage furrow Plant cells: cell forms a cell plate (new cell wall) in the middle of the cell

Label the animal cell and the plant cell

Practice labeling the steps of mitosis

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Prophase Metaphase Anaphase Telophase

2 new identical cells

Regulating the Cell Cycleo Cyclins: proteins that regulate the cell cycle along with enzymes that activate them.o Sometimes, cells lose control of the cell cycle by failing to make certain enzymes,

overproduction of enzymes, or production of other enzymes at the wrong time.

Uncontrolled Cell Growtho Cancer: uncontrolled cell growth.o The result of changes in one or more of the genes that produce proteins involved in

regulating the cell cycle.o Cancer cells do not respond to the signals that regulate cell growth.o Leads to tumors

Cancero 2nd leading cause of death in the USo Lung, colon, breast, and prostate cancers are the most common types.o Causes:

Genetic factors Environmental factors - people in different countries develop different types of

cancers at different rates.3.2 Understand how the environment, and/or the interaction of alleles, influences

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the expression of genetic traits

3.2.1

Explain the role of meiosis in sexual reproduction and genetic variation Unpacking:• Recall the process of meiosis and identify process occurring in diagrams of stages. (middle school review) Note: Students are not expected to memorize the names of the steps or the order of the step names. • Infer the importance of the genes being on separate chromosomes as it relates to meiosis. • Explain how the process of meiosis leads to independent assortment and ultimately to greater genetic diversity. • Exemplify sources of genetic variation in sexually reproducing organisms including crossing over, random assortment of chromosomes, gene mutation, nondisjunction, and fertilization. • Compare meiosis and mitosis including type of reproduction (asexual or sexual), replication and separation of DNA and cellular material, changes in chromosome number, number of cell divisions, and number of cells produced in a complete cycle.

Types of reproduction:

Asexual Reproduction:o Reproduction that involves only one parent.o **** offspring is identical to parento ***** no genetic variationo Types:

Mitosis: in your somatic cells (body cells); in unicellular eukaryotes Binary Fission: prokaryotic (bacteria cells) Budding: yeast Regeneration: flatworms, starfish

Sexual Reproduction:o Reproduction that involves two parentso Offspring is different than parent, they are uniqueo Genetic variation occurso Joining of 2 gameteso Sex chromosomes determine sex. Sex chromosomes

are X or Y; XX is a girl, XY is a boyo Fertilization:

when sperm meets egg (23 chromosomes + 23 chromosomes)

a zygote (46 chromosomes) is created – the zygote undergoes mitosis to become an embryo, then fetus, then baby.

o Types: meiosis

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Asexual Reproduction vs. Sexual Reproduction

Needed vocabulary: o Genes: a sequence of DNA that codes for a protein and determines a trait.Genes are

located on chromosomes, which are composed of DNA.o Chromosomes: rod-shaped structures that carry thousands of genes. Made up of 2

sisters chromatids and a centromere that holds them together.o Homologous chromosomes: found in somatic (body) cells, 2 chromosomes containing

the same geneso Diploid (2n): a cell with 2 of every chromosome, example: body cello Haploid (n): a cell with only 1 of every chromosomes, example: sex cell or gametes

KaryotypeA picture of the chromosomes found in an individual’s cell

Humans -> 46 chromosomes in 23 pairs

Pairs 1-22: autosomes

Pair 23: sex chromosomes (X and Y): XX: female; XY male

Is the karyotype to the right a male or female?

_________________________-

The karyotypes to the right show chromosomes for a diploid

cell and a haploid cell

Meiosiso Process by which the number of chromosomes is cut in half through the separation of

homologous chromosomes in a diploid cell. o Needed for sexual reproduction.o Produces gametes (sex cells)o The result of meiosis is 4 new cells with ½ the number of chromosomes as the parent cell.

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o **** Daughter cells different than parents.o 8 steps: kind of like mitosis twice

Process of Meiosis o Interphase (DNA replication)o Meiosis I – (PMAT)o Meiosis II – (PMAT)o Cytokinesis: (cytoplasmic division)o Crossing over: homologous chromosomes exchange portions of

chromatids during Prophase I of meiosis. *** causes Genetic Variation **

Notice in the picture to the right- Original cell has 4

chromosomes- Homologous

chromosomes pair during meiosis 1 and CROSSING over occurs.

- Homologous chromosomes also separated during meiosis 1 creating 2 haploid cells

- During meiosis 2 sister chromatids separate producing 4 new cells with 2 chromosomes each

Mitosis vs. MeiosisAsexual Reproduction

Needed for sexual reproduction

Produces 2 genetically identical diploid daughter cells

Produces 4 genetically different haploid daughter cells

NO genetic variation Allows Genetic variation

Allows an organisms body to grow and replace cells.

Allows organisms to produce sex cells

Chromosomes number stays the same

Chromosomes number is different

Occurs in somatic (body cells)

End product is gamete (male= sperm, female=egg)

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