Nucleic Acids and Cell Reproduction

Nucleic Acids Organic Compound 2 types of nucleic acids: DNA: deoxyribonucleic acid RNA: ribonucleic acid Carries genetic material

Nucleotide Is the monomer (small molecule) that makes up a nucleic acid Made of a phosphate group, deoxyribose (5 carbon sugar) and a nitrogen base

They are complementary Nitrogen bases in DNA: Adenine (A) Thymine (T) Guanine (G) Cytosine (C) A and T always bond C and G always bond They are complementary

DNA Model Constructed in 1953 James Watson- Biologist from US Francis Crick- Biophysist from England Discovered the double helix model Looks like a twisted ladder Backbone of sugars and phosphates Nitrogen bases make “rungs” of ladder Held together by weak Hydrogen bonds

Purines: Adenine and Guanine Double Ringed Nitrogen Bases Pyrimidines: Cytosine and Thymine Single Ringed Nitrogen Bases

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DNA Replication DNA makes exact copies of itself Happens every time a cell divides Steps of replication: DNA unwinds by using the enzyme DNA helicase DNA polymerase adds new bases beginning at the replication fork DNA polymerase edits for errors

RNA Ribonucleic Acid Structure Three types of RNA: RNA Base Pairs: C & G A& U Ribonucleic Acid Structure Single strand Ribose Uracil instead of Thymine Uracil pairs with Adenine Three types of RNA: mRNA: Messenger RNA tRNA: Transfer RNA rRNA: ribosomal RNA

Gene Expression Taking information from DNA and making proteins Uses all three types of RNA Happens in two stages: Transcription (writing): information is given to mRNA from DNA Translation (telling): mRNA uses the information to make proteins

Transcription (Writing) DNA is giving the information to the mRNA Happens in the nucleus ~Terms to Know~ RNA polymerase: Enzyme that tells transcription to begin Promoter: A sequence of DNA that acts like a green light for transcription Terminator: a sequence of DNA that acts like a red light for transcription

Process Happens in the nucleus RNA polymerase binds to the promoter (green light) on the DNA molecule. The polymerase moves down the DNA strand adding complementary bases for the new RNA molecule A bonds with T -C bonds with G Polymerase adds bases until it reaches the terminator (red light) A new mRNA strand is formed

mRNA The mRNA that was formed in transcription has the following functions: Carries heredity information to the site where proteins are made (ribosomes) Is a template when amino acids are made Amino acids are made according to the instructions found on this mRNA strand

Translation (telling) mRNA carries information to the ribosome In the cytoplasm Where proteins are made rRNA is a structural portion of the ribosome mRNA then gives the information to tRNA tRNA acts like a translator, changing the information into amino acid sequences Proteins are then made from these sequences

Codon Three nucleotide sequence found on tRNA These three nucleotides stand for an amino acid Specific codons code for specific amino acids Example: tRNA codon- AGC Amino acid-Serine tRNA codon-AAU Amino acid-Leucine tRNA codon-UUU Amino acid-Lysine AUG is a Start Codon- Where translation begins UAA, UGA, or UAG are stop codons- Where translation ends

Some things to remember… Proteins are made of amino acids Proteins are made on ribosomes (floating in cytoplasm or embedded in rough ER) Proteins are enzymes Proteins also make up hair, skin, parts of blood, muscles…etc

Comparison of DNA and RNA 1. Double Stranded Single Stranded 2. Thymine Uracil 3. Nucleus Cytoplasm 4. Deoxyribose sugar Ribose sugar

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Chromosomes Genetic information is carried in DNA as chromosomes Rod-shaped Occur in pairs- Homologous pairs (same size and shape) Cells have specific numbers of chromosomes Cells with both chromosomes are diploid (2N) Humans 46 chromosomes •23 pairs Cells with one chromosome of the pair are haploid (N) Humans 23 chromosomes (sperm and egg)

Chromosomes…cont. Autosomes: Chromosomes other than sex chromosomes (first 22 pairs-44 total) Sex Chromosomes: Determines the sex of the individual (23rd pair-2 total) XY= Male -XX= Female

Karyotype Karyotype: Picture of paired human chromosomes arranged by size

Mitosis Cell division that results in two exact daughter cells There is an exact replication of the nucleus Cell Cycle: G1 Phase: Cell growth S Phase: DNA Replication G2 Phase: Growth and prep. for mitosis Mitosis: nucleus is divided into two cells Cytokinesis: Cytoplasm divides

Anaphase Telophase Cytokinesis G1 S G2 Prophase Metaphase Anaphase Telophase Cytokinesis

Interphase G1, S and G2 phases Period between cell divisions DNA is replicated Time for growth and normal cell activities Centriole divides and starts to move

Prophase Metaphase Anaphase Telophase PMAT

Prophase Centrioles move to opposite sides of cell Chromosomes become thicker and coil Spindles form Nuclear membrane and nucleolus disappear

Metaphase The two centrioles are at opposite poles The paired chromosomes line up in the MIDDLE Centromere attaches to spindles

Anaphase Chromatids separate Chromosomes move to opposite poles

Telophase Chromosomes un-coil Spindles disappear Nuclear membrane and nucleolus re-appear Cytokinesis begins Cytoplasm divides

Meiosis Occurs in sex cells (gametes-sperm and egg cells) Only occurs in organisms that reproduce sexually Same steps as mitosis, except process is completed twice Divides chromosome number in half 2n (diploid) to n (haploid)

Results in 4 gametes Spermatozoa: Sperm Ova: Egg

Sexual vs. Asexual Reproduction Sexual Reproduction: Need a sperm and egg cell Genetic diversity Species can adapt (change) for environment quickly Slow population growth Asexual Reproduction: Can reproduce without a partner No genetic diversity Quick reproduction, may be good for survival rates but organism will run out of resources quickly

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