Cell Reproduction Unit Part 1: Overview

Objectives Be able to explain the difficulties a cell faces as it increases in size Be able to compare and contrast sexual & asexual reproduction Be able to describe the structure of a chromosome Be able to identify the differences in structure between prokaryotic chromosomes and eukaryotic chromosomes Be able to explain the differences between sex chromosomes and autosomes

Limits to Cell Size Nearly all cells grow by increasing in size At some point, they divide There are two main reasons cells divide rather than continue growing: Information Overload The larger a cell becomes, the more demands the cell places on its DNA Exchanging Materials A larger cell is less efficient in moving nutrients and waste materials across the cell membrane

Surface Area to Volume Ratio The size of a cell is limited by the relationship of the cell’s outer surface area to its volume, or its surface area–to–volume ratio As a cell grows, its volume increases much faster than its surface area does Why is this important to cells? This trend is important because the materials needed by a cell, such as nutrients and oxygen and the wastes produced by a cell, such as carbon dioxide must pass into and out of the cell through its surface.

Division of the Cell Before a cell becomes too large it divides into two “daughter” cells Cell Division: is the process by which a cell divides into two new daughter cells

Cell Division & Reproduction All organisms produce new organisms like themselves During reproduction, organisms transmit hereditary information

Two Types of Reproduction Asexual Reproduction: produces new organisms that are exactly the same as the original organism Examples: strawberries, amoebas, bacteria, starfish, onions etc. Sexual Reproduction: produces a genetically unique organism from the combining of the parents’ DNA Examples: humans, tigers, some plants, whales, etc.

Compare & Contrast Asexual Reproduction Sexual Reproduction Needed for the survival of a species Happens faster Offspring are exact copies of parents Lack of genetic diversity Needed for the survival of a species Takes longer Offspring are a combination of parents DNA Lots of genetic diversity

Visual Analogy Activity In the assigned groups, discuss the following and be prepared to share with the class. How could cell growth create a problem that is similar to a traffic jam? How does a cell solve the “traffic jam” like a growing city would? Why are cells concerned with “traffic jams”?

Facts about DNA It is a long, thin molecule that stores ________ ______________. It is made of nucleotides Nucleotides are made of: In human cells, its consists of approx. 3 billion nucleotides In eukaryotes, DNA is found in the _________. In prokaryotes, DNA is found in the ___________. a sugar, a phosphate, and a nitrogen base

Chromosomes Chromosomes are rod-shaped structures made of DNA & proteins The DNA & proteins are tightly coiled together The proteins that eukaryotic DNA wraps around are called histones Histones help maintain the shape of a chromosome & keep it tightly packed

Chromosome Structure of Eukaryotes Nucleosome DNA double helix Coils Supercoils Histones

Chromosome Structure Each chromosome consists of 2 identical halves called ___________ The 2 chromatids are held together by a ______________.

Chromosome Structure Normally DNA is not so tightly coiled into chromosomes Chromosomes only appear right before cell division When cell division is not occurring, DNA is less tightly coiled as __________. Why is the DNA not kept tightly packed all the time? Because it is easier to copy (transcribe) in its chromatin form, which happens before division occurs

Chromosome Number Every species has a characteristic number of chromosomes in each cell Human & animal chromosomes are categorized into 2 groups: ____________ & _______________.

Sex Chromosomes & Autosomes Sex chromosomes: are the chromosomes that determine the sex of an organism In humans, they are either X or Y Females are XX Males are XY Autosomes: are all the other chromosomes of an organism Humans have 44 autosomes (22 pairs)

Chromosome Numbers Every organism produced by sexual reproduction has 2 copies of each autosome One copy comes from _____ and the other comes from ______. The 2 copies of each autosome are called homologous chromosomes Meaning they are the same size, shape and carry the same traits

Human Karyotype A karyotype is pictorial diagram showing all the chromosomes of an organism

Chromosome Numbers: Diploid vs. Haploid Cells Diploid cells: have 2 sets of homologous chromosomes All human cell except the sex cells are diploid Abbreviated 2n In humans, 2n = ____ or ____ pairs Haploid cells: have only 1 set of chromosomes Sperm & egg cells are haploid Abbreviated 1n In humans, 1n = ____